Role of Humans in Plant and Landscape Manipulation Discussion

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What key shifts in our own thinking about the role of humans in plant and landscape manipulation did you notice after reading Fuller and Rindos? What lessons might be relevant here for our current world?Symbiosis, Instability, and the Origins and Spread of Agriculture: A New Model [and Comments
and Reply]
Author(s): David Rindos, Homer Aschmann, Peter Bellwood, Lynn Ceci, Mark N. Cohen, Joseph
Hutchinson, Robert S. Santley, Jim G. Shaffer and Thurstan Shaw
Source: Current Anthropology, Vol. 21, No. 6 (Dec., 1980), pp. 751-772
Published by: University of Chicago Press on behalf of Wenner-Gren Foundation for
Anthropological Research
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CURRENT ANTHROPOLOGY
Vol. 21, No. 6, December 1980
? 1980 by The Wenner-GrenFoundation forAnthropological Research 0011-3204/80/2106-0002$02.55
and the Originsand
Symbiosis,Instability,
A New Model
Spread of Agriculture:
by David Rindos
INTRODUCTION
The originsofagriculture
and its subsequentspreadhave been
of concernto both naturaland social scientistsforover 100
years.The studyofagricultural
originsis farmorethanmerely
the investigationof a particularshiftin man’s subsistence.
is seenby mostpeopleas thefoundation
Agriculture
ofmodern
civilization.It is frequently
heldthatonlyagriculture
permitsa
societytheluxuryofexcessproductionand thatalongwiththis
excessproductioncomes the developmentof the hallmarksof
civilization:writing,metalworking,
and the establishmentof
well-defined
economicclasses. Despite the significance
of agriculturalorigins,our understanding
of thisphenomenonis far
fromsatisfactory.
We lack any unifiedtheoryto explainboth
howagriculture
aroseand whyit shouldhave arisenat all.
Variousapproacheshave been takentowardstheexplanation
of the initial appearance of agriculturalsubsistence.Most
workersin thesocial scienceshave begunby lookingintoman’s
cultureforthe factorswhichcould explainthe developmentof
pristineagriculturalsocieties. Bachofen (1967 [1861]) and
Frazer (1912) believedthatagriculturedevelopedout of traditionalsexual rolesand the divisionsoflabor that theycreated.
Allen (1897) and Hahn (1909) presentedargumentsseekingto
understandagricultureas an outgrowthof ritualisticand religiouspractices.This approachhas been recentlydevelopedin
greatdetail by Isaac (1970). Otherworkershave ascribedthe
originof agricultureto the influenceof climaticevents (Pumpelly 1908,Childe 1951,Wright1968). Finally,certainauthors
have alwaystakenwhatmaybe describedas a “commonsense”
view of the originof agriculture:that agriculture,like other
is theresultofan “invention.”Carter
technological
innovation,
(1 977) is a contemporary
authoradheringto thisviewpoint.
Recently,ecologicalparadigmshave cometo dominateagriculturaloriginstheories.Ecological theoristshave developed
thepioneeringworkofthebiologistsDe Candolle(1959 [1886])
and Vavilov (1926) and thegeographerSauer (1936, 1969).The
DAVID RINDOS is a graduatestudent
at CornellUniversity
and
teaching
and research
assistantat theUniversity’s
L. H. Bailey
Hortorium
(467MannLibrary,
CornellUniversity,
Ithaca,N.Y.
14853,U.S.A.).Bornin 1947,hereceived
hisB.S. inruralsociology
from
Cornell
in 1969andhisM.S. inplanttaxonomy,
witha minor
in anthropology,
in 1980.He has beenpalaeoethnobotanist
with
theCornellArchaeological
Projectin Cyprusand in Honduras.
His research
interests
are thesystematics
oftheCompositae
and
theinteraction
ofplantsand man.His Master’sthesisis entitled
” GenericDelimitation
in theVerbesinoid
Heliantheae(Compositae).I. The GenusZexmenia.”
The present
paperwas submitted
in finalform8 I 79.
hallmarkof the ecologicaltheoristis thathe places major emphasis on the interactionbetween man and his immediate
comworkersstressdifferent
environment.
Of course,different
Workersplacinggreatemphasison
ponentsofthisrelationship.
a theoretical”equilibrium”betweenpopulationand the environment
includeBinford(1968),Meyers(1971), Cohen(1975,
1977),and Flannery(1965,1973).Most oftheseworkersexplain
the originor adoptionof agricultureas the resultof attempts
to correcta disturbedequilibriumbetweenpopulationand the
environment.
Others,such as Lewis (1972) and Harris (1969,
1972), along with Flanneryin a paper otherthan those just
cited (1969), stressthe importanceof the developmentof new
techniquesand culturalpatternsto the originof agricultural
systems.
Most of thistheorizing
on the subjectofagriculturalorigins
has been permeatedby two fundamentalconcepts:that agriin originand that its adoptionand
culturewas revolutionary
subsequentdevelopmentweredue to intentionalpractices.As
notedby Harlan, de Wet,and Stempler(1976:3), “the idea of
an agriculturalrevolutionas elaboratedby V. GordonChilde
fortheNear East was basicallyappliedto thesocialand cultural
economies.”Onlyrecentlyhas
consequencesof food-producing
thisidea begunto be challenged.The agricultural
way oflifeis
now beginningto be seen as the resultof a seriesof gradual
changes(cf. MacNeish 1964,Bray 1974,Higgs 1976, Pfeiffer
1976). Even today,most modelsforthe originof agriculture
containat least some elementsof culturalor individualintention-eitherto explaintheinitialappearanceof thetechniques
and plants of agriculturalsystemsor to elucidatethe survival
and dispersalofagricultural
systems.Corollaryto,and perhaps
underlying,
theseconceptsis the beliefthat agriculturefacilitatesthedevelopment
ofa “superior”economy-onewithclear
and substantialadaptivebenefitsto thesociety.This adaptiveinvokedto explainthe maintenanceand
nessis also frequently
it is held,is maineconomies.Agriculture,
spreadofagricultural
meansto feedlargenumtainedbecauseit is themosteffective
bersofpeople;agriculture
spreadsbecauseits greateradaptiveness allows it to spread at the expenseof more “primitive”
meansofproduction.
I shallhereintroducea newmodelfortheoriginand developmentof domesticatedplantsand agriculturalsystems.Rather
thanrelyingupon the assumptionsjust mentioned,thismodel
views agricultureas the outgrowthof evolutionarypotentials
feedsupon
whichmaydevelopwheneveran animalconsistently
any set offoodplants.Intentand inventionare notdenied,but
they are regardedas unnecessaryto the model. Parsimony
would suggestthat if agriculturaloriginsmay be explained
Vol. 21 * No. 6 * December1980
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751
withoutuse ofintentor invention,
thentheseconceptsmay,for
If themodelforagriculturaloriginsand thedomestication
of
thepurposesofthismodel,be set aside.’
plants presentedhere proves useful,its greatestcontribution
Given the evolutionary
means by whichagriculturalplants
maycomefromtherecognition
thatwe are notfacinga qualitaand systemsdevelop,the originof agricultureis anythingbut
tivelydifferent
set ofproblemsfromthosefacedby our distant
theultimateeffects
revolutionary-although
oftheprocessmay
forebears.The historyof agricultureis a historyof instability
be describedas a revolutionofthefirstorder.The adaptiveness inproductionand ofagriculturally
inducedcrises.Identification
of agricultureis not stressedin this model,althoughit is not
of the factorsresponsibleforthis instabilitymay allow us to
denied that agriculturepermitsgreaterdensitiesof human
takeactionto reduceit. Seen fromtheperspectiveofthemodel,
populationthan mostotherformsof subsistence.Instead,emmanyof ourbestattemptsat increasingagricultural
productivphasisis placed upon theinstabilities
whichfirstdomestication itycan be expectedto increasethevulnerability
of thesystem
and then agriculturalproductionintroduceinto subsistence to failureas well;thebestattemptsofourancestorsto improve
strategiesand whichare the basis foragriculture’s”success.”
the productivity
of theirsystemshad similareffects.Whilein
Finally,the relationship
betweenthe originof agricultureand
the past we have survivedagriculturalcrisesand even benethe riseof moderncivilization,whileaddinga certainurgency fitedfromthem,however,we are no longerin a strictlycomto the study of the problem,is not addresseddirectlyhere.
parable situation.The consequenceof agriculturalcrisisis no
Discussionof thisdifficult
problemwouldof necessitytake us
but thepossibilityof starvation.By apprelongeremigration,
farbeyondthe consideration
ofagriculturalorigins.Neverthe- ciatingthe historyof agriculturalsystemswe may be better
less, if thismodelhas any heuristicvalue, implicationsmay be
preparedto developourpresentsystemsto satisfythedemands
drawnfromit whichgo beyondthe meredescriptionof a new
of the future.
modeoflifeforman.
In the model, domesticationoccurs beforethe originand
Modernagriculturaldevelopmentschemesare a responseto
developmentof agriculturalsystems.Domesticationis thereatheshortagesoffoodand resourcesthatplague so muchof the
son agricultural
systemsdevelop.Althoughthe importanceof
world.Allagricultural
systemsappearproneto occasionalcrises
domesticationper se to a societydecreaseswith the rise of
in production.Besides their immediateeffectsupon human
agricultural
systems,domestication
does not cease. It continues
healthand survival,shortagesoffoodfrequently
the plants
have deleteri- withinthe agriculturalcontext,furthermodifying
ous effects
uponthestabilityofpoliticaland economicsystems. undercultivation.It may also occurwithplantsoutsideof the
The importanceof theinteractionofpopulationgrowth,dwin- agriculturalecology.Domesticationis theresultoftheevolution
dlingnaturalresources,and recurrent
shortagesof foodplaces
ofa symbiosis
between
man and plant.
the studyof agriculturalsystemsin the mainstreamof human
The best way to understandthe changesthat have occurred
concern.The prospectof foodshortagesencouragesthe breed- in domesticated
plantsis to lookat therelationship
betweenthe
ing of improvedcrops and the developmentof moreefficient plantand theanimalwhichfeedson it. Two ofthemostimporcroppingsystems.Success in theseprogramsencouragesrelitant effectsof domestication
are (1) intensification
of the muance upon fewerand fewerspeciesofplantsand upon an ever
tualisticrelationship
betweenanimal and plant and (2) excludecreasingnumberof varietiesof a givenspecies.Agricultural sion ofotheranimalswhichmightalso be competingforaccess
productionalso tendsto becomemorelocalized,to take advanto theplant.These effects
are usuallymediatedby morphologitageoffavorableenvironmental
cal change.One of the mostimportantfactorsin the evolution
conditions,
and to allowforthe
exploitationof economiesof scale. Yet, as is well recognized, ofthecultivatedplantis theisolationofthepotentialcultivated
monocultures
are extremelyvulnerableto catastrophicfailure plant, by eithergeneticor spatial mechanisms,fromthe proas a resultofdisease,pests,and climaticextremes.
takenhere mayalso
genitorspecies.The viewofdomestication
Today, man reliesuponabout 20 speciesofplantsto provide
be used to accountforthe evolutionof weedsand forthe nonmost of his food (National Academyof Sciences 1975). Yet
domestication
ofpotentiallyvaluable crops.
hundredsof species of plants have been domesticatedand
The transitionfrommutualisticdomesticationto evolved
thousandsutilized.Remarkably,no majorcrophas beendomesagriculturalsystemswas mediatedby environmental
maniputicatedfromthewildsincetheearliestdaysofagriculture.
lation.Humanactivitiessuchas thefellingoftreesorthesetting
Even
our best attemptsat improvement
offirescannothelpbut have had effects
of existingcropshave been
uponthelocal environless than totallysuccessful.Recentlywe have begunto under- ment.The major effectof theseactivitieswas the concentrastand that plant breedingand the successfulintroductionof
tion of domesticatedplants in localized areas. This permitted
new,improvedcultivarsmay inadvertently
therealizationofa newseriesofevolutionary
be acceleratingthe
potentials.I shall
loss ofmuchofthevariationin thecropsgrownby man. Atten- presenta dynamicand interactivemodel to account for the
tion has come to be directedtowardsthe importanceof the
originand subsequentspreadofagriculturalsystems.
conservationof gene pools forcultivatedplants. We are also
is based on environmental
Agriculture
manipulation.Ecologto understandthatthebreedingofimprovedvarieties ical limitsupon plant productivity
beginning
are thusreduced.Agriculof crop plants is, paradoxically,oftenaccompanied by intureis a set of integrated
whichaffects
theenvironment
activities
creased susceptibilityof the crop to previouslyunknownor
inhabited
its lifecycle.Agribythedomesticated
plantthroughout
unimportant
pests and diseases. We are finallybeginningto
cultureservesto increasethe domesticity
of the plant. Howrecognizethatagricultureis a dynamicsystem-thatthe agriever,it has major effectsupon the communityof plants that
culturalecologyexistingin any regionis the productof the
are utilizedin agriculturalsystems.It tends to increasethe
interactionofnumerousfactorsoverlongperiodsoftime.Only
average yield of domesticatedplants. Competitionwithina
certainparts of the agriculturalecologyare completelyunder
speciesof domesticatedplantstendsto selectthoseindividuals
humancontrol.As we beginto understandthefunctioning
best adapted to agriculturalpractices.Competitionbetween
and
the evolutionof theagriculturalecology,however,our control species of domesticatedplants tends,in a similarmanner,to
over it is likelyto increase.Part of this understanding
select forthosespecies best adapted to agriculturalpractices.
must
come froma considerationof the originand developmentof
Thus, over time,althoughyieldincreases,it comesfromfewer
agriculturalsystemsand an investigation
of the factorswhich plant species.
controland limitthedomestication
Localizationof agriculturalproduction,however,is accomofplants.
forsurvivaland
panied by convergencein the requirements
reproductionin species of domesticatedplants. This conver1 Elsewhere I have given the issues of intent and inventionexgenceand,indeed,thelocalizationofproductionitselfintroduce
tendedtreatment(Rindosn.d.). The viewofhuman behaviorpresentnew instabilitiesinto agriculturalproduction:what is a bad
ed here should not be confusedwith “sociobiology”; instinctand
geneticsare also set aside.
year forany givenagricultural
plant is likelyto be a bad year
752
CURRENT
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ANTHROPOLOGY
many
by concentrating
plants.Agriculture,
forall agricultural
plants in one area, may also encourageexcessivedamage by
disease,insects,and herbivoresand thusdecreaseyield.Instaare expressedas periodsof greatlyrebilitiesin productivity
duced yield. These crises cause the emigrationof the excess
populationfromagriculturalsocieties.These emigrantpopulaforthedispersaloftheagriculturalway of
tionsare responsible
life. Selectionhas favoredthe spread of agriculturalsystems
which maximizeinstabilityin production.Maximization of
instabilitybringswithit maximizationof dispersals.Thus the
mostsuccessfulagriculturalsystemshave been thosethat are,
at least in the broadestsense,the least “adapted” agricultural
systems.
Rindos:ORIGINS AND SPREAD OF AGRICULTURE
Hartzell (1967) has reportedon one particularant/acacia
relationship.The ants inhabithollow,enlargedthornson the
acacia and receivea sugaryexudatefromspecialfoliarnectaries
at the base of the leaves. They also harvestmodifiedleaf tips
calledBeltrambodies,whichare richin bothproteinsand lipids.
Theseare usedto feedtheant larvae.The antspatrolthefoliage
insects.Whenants were
and removeand feeduponherbivorous
experimentallyremoved from acacias, the plants were so
and insectsthatall died within
severelyattackedby herbivores
a year.Otheracacias are protectedby theirants fromherbivore
theplantis attackedand given
predation;anyanimaldisturbing
numerouspainfulbites (Hockeng 1975).
The loss of chemicaldefensemechanismswithina speciesof
DOMESTICATION AND SYMBIOSIS
acacia involvedin a mutualisticrelationshipwithants is apparentlycommon.Ant-acaciaslack the biochemicaldefense
ANIMAL-PLANT INTERACTIONS
mechanismpresentin otheracacias (Rehr,Feeney,and Hanzen
plantshave
Domesticationis best understoodas an interaction 1973). In an analogousfashion,manyhuman-crop
Coevolution.
is exeggplant
wild
the
systems:
defense
chemical
lost
their
betweenman and theplantson whichhe feeds.2It wouldseem
wild
of
flesh
bitter
the
1976:80);
(Choudhury
bitter
tremely
as an adaptaless thanaccurateto describesuchan interaction
(1975)
and
Bemis
for
Whitaker
is
sufficient
species
Cucurbita
tion of or by man to the demandsof continuedsurvival-we
to postulatean originaldomesticationof thesefruitsfortheir
may just as easily describethe processof adaptationof or by
seeds; the domesticationof lettuce (Latuca sativa) has been
the plant, forit too benefitsfromthe association.By placing
in latex
the
emphasisupon theactionsof man we neglect fundamental accompaniedby a reductionofspininessand a decrease
can
oleraceae)
(Brassica
cabbage
wild
1976:39);
content
(Ryder
contribution
made by the domesticatedplant to the developdanof
bitter
and
quantity
the
much
as
four
times
as
contain
exist
withcould not
mentof agriculturalsystems.Agriculture
gerousglucosimatesas cultivatedstrains(Josefsson,cited in
out domesticatedplants. Domestication,as seen here, is a
1976:49); cassava (Manihot esculenta)has two
Thompson
natural evolutionaryprocessby means of whichanimalsand
one
poisonouswhen raw and the otherlacking
highly
forms,
plantsare able to increasetheirfitness.Coevolution-a typeof
of beingcooked and eaten withprelimiand
capable
poisons
evolutioninvolvingtwo geneticallyunrelatedspecies-occurs
of the organismspositively narytreatment-thepresenceof toxinsprobablybeing correwheneverthe interrelationship
lated, at least in part,withmethodsof cultivationin differing
affectstheir potential for survival. The relationshipwhich
describedas a symbiosis. agriculturalsystems(Rogers and Appan 1973, Rogers 1965).
resultsfromcoevolutionis frequently
The hoardingof seeds is widespread
Storageand harvesting.
Coevolutionis widespreadin nature.Pollination,seed discan
persal, and even predation frequentlyhave coevolutionary in theanimalkingdom,and, as it relatesto plantdispersal,
of
plants.
history
in
the
evolutionary
significance
be
of
major
withinwhich
aspects.Coevolutionprovidesa usefulframework
Various birds,includingnutcrackers,jays, and woodpeckers,
to observedomestication.By means of his interactionswith
and mor- are knownto storeseeds of such plants as pine, beech, oak,
plants,man inevitablyinfluencestheirdistribution
phology.These changes,of course,do not occur by the direct chestnut,filbert,and variousPrunus species. Small mammals
storeedibleseedsin their
and chipmunks
suchas mice,squirrels,
influenceof man’s activityon the plants. Rather,theyoccur
1972,Stebbins1971).
der
Pijl
caches
(van
in
special
and
nests
over manygenerationsas certainplants-the morefit-leave
dried
made
of
grassesand weeds.
up
a
hay
and
store
guard
Pikas
greaternumbersofprogeny.
Guardingof storesis also commonin various birds (Emlen
The most strikingevidenceforthe coevolutionaryview of
1973:164). Janzen(1971) notesthatseedsofstoredspecies can
and agriculturaloriginsis the existenceof widedomestication
soils near
be
foundgrowingto adult statusin thenitrogen-rich
spread nonhumanagriculturalsystems.Domesticatedplants
were
“lost”
seeds
these
that
assumed
be
It
can
nest
entrances.
have establishedrelationshipswithmany animals otherthan
resource
a
useful
provide
these
plants
Clearly,
or
“rejected.”
man. In a fewinstances,theseotheranimalshave incorporated
fortheinhabitantofthenest.Muskrattrappersin centralNew
manipulationintotheirbehavioral
techniquesofenvironmental
rice
and we may thereforecall the resultantsystems York reportthatlargestoresofarrowheadtubersand wild
repertoires,
dens.
muskrat
in
found
can
be
agricultural.Agriculturehas generallybeen characterizedby
forour purposesis the phenomenonof
Far moreinteresting
such actions as sowing,protection,and harvestingor by the
Harvesterants
seed
(myrmecochory).
dispersal
ant-mediated
existenceofmorphologically
distinctcultivatedplantswhichare
have establisheda symbiosiswithspeciesof plants frommore
None ofthese
adapted to thebehaviorsinvolvedin agriculture.
63 familiesof flowering
plants
phenomenais restrictedto the human-plantinterrelationship. than 223 genera representing
(Nesomn.d.). These ants collectand therebyoftendisseminate
Whilenumerousexamplesofprotectionof plants
Protection.
theseedsoftheseplants.The antsare “apparentlyable to conby animalsmightbe given,I wouldlike to describeherea paroftheseedstheycollectand also exertcontrolthegermination
ticularlycomplicatedformof protectionactivitywhich has
on thevegetationin thevicinityofthenest”
influence
siderable
evolvedin the behaviorof certainants. Here we finda highly
(Hockeng1975:83).
developedmutualisticrelationshipbetweenants and plants in
Harvesterants have developedquite sophisticatedformsof
whichthe plants providedomiciles,food,or both forthe ant.
behaviorto protecttheirseed stores.At least some species of
In “return,”theant protectstheplant.
ants willremoveseeds thathave becomewetfromthenestand
drythemin thesun.Many speciesoftheants “thresh”theseed
2 In this analysis I am restricting
myselfto the originof planttheygather,and moundsof chaffmay be foundin the vicinity
human relationships.To add an analysis of animal domestication
of the nest.It appears that bothant and plant benefitby this
would substantiallyextendthe lengthof thisessay. Furthermore,
all
agriculturalsystemsare ultimatelybased upon plant domestication;
association(Hartzell 1967:127):
human-animalrelationships
lackingthiselementare generallytreated
The
anddrought.
coldperiods
Theantis assureda foodsupplyduring
as a separate phenomenon(i.e., pastoralism).Finally, the treatment
against
and it is protected
plantspeciesis aidedin its distribution
hereis at least in part dictatedby my trainingas a botanist.
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and coldby beingstoredin theunderground
galexcessive
drought
collecttheirfoodsupplyin
leriesoftheants.Sincetheantsnormally
thisis an important
inthesurvival
factor
excessoftheirrequirements,
of the plantspeciesduringclimaticchangesthatwouldnormally
themaboveground.
destroy
are not limstorage,and controlovergermination
harvesting,
ited to the relationshipbetweenplants and man. Similarly,
of the plant throughcultivationis
modification
morphological
withman.Numerousspecies
to plantsinteracting
notrestricted
of insectshave establishedsymbioticcultivationrelationships
is characterized withfungi.More than40 speciesofbeetles,knownas “ambrosia
Stebbins(1971:243) notesthatmyrmecochory
modifications
in the plant:
by a wholeseriesof morphological
beetles,”as wellas somewoodwaspscultivatefungusas sources
to theirrelatives
In comparison
… [these]plantshavethefollowing of food.These insectsboreinto,but do not directlyeat, wood
theflower
stalksarerelatively
characteristics:
low,and thepeduncle and otherplant tissue.Instead,theyinoculatetheplant tissue
whentheseedis ripeso thatthematurecapsuleis
becomesrecurved
withsmallamountsoffungus.This fungusis usuallycarriedby
closeto theground.The capsule… does notdehisceregularly
by
the insectsto the hostplant in specializedorgans,mycetangia.
and overa relatively
longperiodof
valvesor pores,butirregularly
organsin the various
Mycetangiaare derivedfromdifferent
time…. Thismakespossiblerepeatedvisitsbytheantsto thesame
groupsof ambrosiabeetles,and we may thusassume that the
haveseveralmodifications.
Sometimes habitoffunguscultivationis polyphyletic
plants.The seedsthemselves
in originevenforthis
theyhave a specialoilyseedcoat; theantsremovethisafterthey
groupofinsects.In all cases,fungusservesas thechiefsourceof
have carriedthe seeds to theirnests,and thentheydiscardthe
stagesoftheinsect.
fat-bearing foodforall thedevelopmental
strippedseeds.Moreoften,each seed has a particular
The fungithat are cultivatedcome frommany different
appendagewhichthe ant clipsoffwithits mandiblesand carries
generabut can be broadlyclassifiedintotwo groups.Some are
ofthe
afterithas transported
theseedsto thevicinity
underground,
nest.
knownoutsideof the symbiosis,but the majorityare highly
specializedand are not knownto existindependently(Baker
ofant-dispersed
Changesin themorphology
plantsare adapta1963). These fungiare generallyhard to classifybecause they
of the symbiosis.Traits of
tionsnecessaryto the functioning
nothave a truesexual cycle,insteadbeingadapted to vegedo
domesticatedcropssuch as indehiscencemay be viewedin the
tativedispersalsby theirrespectiveinsectvectors.3It is imporsame manner.
tant to note that the funguswill not growin the host plant
Transportationof the seeds to the vicinityof the nest can
withoutthepresenceoftheinsect.The insectin factmaintains
of fairlylarge populationsof the
allow forthe establishment
pure culturesof its associatedfungiby removingany competplantin an area whereit mostbenefitstheants.Like theestabremoved,the
fungus.If theinsectis experimentally
ing,foreign
lishmentoffoodplantsin thevicinityof mammaliannests,this
alien
is
taken
over
The
insects
also fresite
by
growth.
usually
formof ant dispersalbears strikingsimilarities
to the “dumpquentlypreparespecialbedsofwoodchipsand fecesto enhance
heap” modelsfortheoriginofagriculture.
the growthof the fungi(Francke-Grosman1967). Growing
Furthermore,
myrmecochory
may allow forthe survivalof
otherwiseunadaptedorganisms.Handel (1978) has extensively thesefungiunderlaboratoryconditionshas provento be exComplexmedia that includevitamins,lipids,
tremelydifficult.
studied the competitiverelationshipsof threecloselyrelated
and amino-acidsare required.It appearsthatmanyofthefungi
United
speciesofsedges(Carex)whichgrowin thenortheastern
and extensiveexperimental
States.Bothfieldwork
investigation are dependentuponinsectsecretionsforgrowth.Underlaboratoryculture,thefungusloses thegrowthpatternand morpholhave shownthat one ant-dispersed
speciesis a relativelypoor
ogy
presentin theambrosialstate.
has
survivedbecause it does not have to comcompetitor.It
Antsand termiteshave also developedsophisticatedcultivapete directlywiththe otherspecies.This is because it is distionsymbiosiswithfungi,someofwhichare highlycoevolved.
persedintoa habitat (rottinglogs) whichis unavailableto the
For example,manyspeciesoftropicaltermitesmaintainfungus
others.Antsnestingin rottinglogs dispersethe speciesin the
“gardens” in theirnests. Unlike most termites,these species
vicinityof theirnestsand providea refugeforit. The sedge
lack theintestinalmicroorganisms
necessaryforthedigestionof
thususes theant as its dispersalagentin a race to keep ahead
cellulose.Instead,theircarefully
nurtured
fungusprovidestheir
of the other,morecompetitivespecies.The ant-dispersed
spefoodsupply (Trager 1970). It is again among ants, however,
cies mustmoveintonewhabitatsas theybecomeavailable,for
that we findthe mosthighlydevelopedcultivationanalogues
oncethehabitatis no longera newhabitat(thatis,oncethetree
(Weber1966,Hartzell1967,Hockeng1975,Trager1970). Cultiis completelydecomposed)the plant will be replaced by its
vatorantspreparespecialbeds,generallyofplantdebris,cut-up
relatives.
in special chambersin the ant
and excrement,
leaves, flowers,
Typical of the syndromeof a weedycolonizingspecies,the
nest.The ants are meticulousabout growthconditionswithin
ant-dispersed
sedgehas evolvedseveralothertraitswhichconthechamber;numerousventilationpassagesare dug,and these
tributeto its successin thisrole.It has, on the average,twice
and humidthe seed set of its relatives.It is also typifiedby immediate are openedor closedto regulateboth temperature
ity.To constructthebeds,theants chewthesubstratematerial
germinationof the seeds; the othertwo species requireoverto make a pulpymass and depositit in layersin the chamber.
wintering
beforetheywill germinate.This is also probablyan
adaptationto greaterseed productionand thusthe maximiza- The bed is thenplantedwithpropagulesfrompreviouslymaintainedbeds. Constantcare is giventhe beds. The ants remove
tionof the total seed crop duringthe relativelyshortlifespan
alien fungiand add anal and salivary secretionswhich apofthedisturbedhabitat.The weedycolonizingspeciesmustput
on thegrowthofthefungi.These
parentlyhave a positiveeffect
a great deal of energyinto the productionof seeds. Only by
cultivationactivitiesencouragetheproduction,by the fungus,
maximizingthe potentialfordispersalcan this type of plant
ofsmallwhitishroundbodies,theso-calledkohlrabistructures.
survive.
These structures
are theprincipalfoodoftheant colony.While
The similarities
betweentheant-dispersed
colonizingspecies
underthecare oftheants,thefungusproducesno sexualstage.
and the cultivatedplant are ratherstriking,
but theyare not
mushroom
If the ants are removed,however,the reproductive
unexpectedifwe recognizethat theyare the resultsof a comofremovalof
however,theeffect
mayappear. More frequently,
monprocess.The problemsconfronted
by the cultivatedplant
of the beds by alien fungiand other
the ants is contamination
identical
duringtheearlyphasesofdomestication
are essentially
organismsto thequickexclusionoftheant-fungus.
to thoseofany otherplantmaximizing
itspotentialas a weedy
It is clear thatagriculture
way,be
cannot,in any meaningful
colonizingspecies.Total crop of seeds must be maximizedto
If we tryto findany
interaction.
restricted
to thehuman-plant
allow forthetransportofthe plant to a newlyopened habitat.
activityor collectionofactivitiesto definethe man-plantrelaHowever,the creationof a new habitat is diagnosticforadvanced agriculturalsystems.It is withinthis habitat that
I It would be hard to hold that this is necessarilya resultof the
actionssuchas weedingbecomeimportant.
association;thereare numerousfunginot associatedwithinsectsthat
Morphological
changethrough
cultivation.
Clearly,
protection, possessno sexual stage (the so-calledfungiimperfecti).
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ANTHROPOLOGY
tionship,we are at the same timedefiningotheranimal-plant
To say that man has a different
relationships.
attitudeor approachto the cultivatedplant seemsinsufficient
to distinguish
the human-plantrelationship
fromtheseothers.Further,even
if we grant a qualitative difference
in agriculturalbehavior
betweenman and otheranimals,it seemsunreasonableto assumethatman was necessarilyas consciousofthe evolutionof
agriclultural
systemsin the earlieststages of plant domesticationas he is today.
Rindos:ORIGINS AND SPREAD OF AGRICULTURE
in regionsof highlydiversified
florasin whichthe individual
plant becomesless conspicuous.It wouldthusseemreasonable
to assume that plants whosevegetativeorgansare utilizedby
man were domesticatedafterprotectivebehaviorshad begun
to be practiced.At such a time,plants not possessingdefense
mechanisms
mightbe sparedbecauseoftheirdesirability,
and it
wouldbe possibleforthemto pass thenonprotected
stateon to
succeedinggenerations.
Whenan animal feedsupon the reproductive
propagulesof a
THE EVOLUTION OF DOMESTICATED MORPHOLOGIES
plant,thepotentialforthe developmentofdomestication
symThedomesticated
plant.As we have just seen,domestication
is a
biosesis great.The plantmaybe able to utilizethepredatoras a
particulartype of plant-animalinteractionwhichfavorsthe
dispersalagent.The developmentand elaborationof dispersal
evolutionof certainmorphologicalchangesin the plant. The
symbioseshas been extensivethroughout
nature.Confirmation
is also characterized
relationship
by specificsetsofbehaviorby
of the importantrole of the reproductivepropagule in the
the animal. It is necessaryto stress,however,that domestica- developmentof domesticationsymbiosesmay be seen in the
tiondoes notevolveorthogenetically
or inevitablyintoagricul- typesofcropswhichman generallygrows.Thereare numerous
ture.Indeed, the degreeof developmentof the domestication plants whose vegetativeparts are highly defended,either
relationshipmay vary amongstthe total set of plants with
mechanicallyor chemically,but whosereproductive
propagules
whichan animalmay be interacting.
are edible.This edibilityis frequently
advertisedby the develDifferentdegreesof domesticationmay be seen in manyof
opmentof conspicuouscolorationwhen the propaguleripens.
thecropswhichare cultivatedby man. Sincedomestication
is a
Of course,as would be expected,this advertisingand defense
naturalevolutionary
process,thisis notsurprising;
it is a func- syndromeis not restrictedto cultivatedplants. It is also extionofthefactthattheplantis notexperiencing
selectiveprestremelywidespreadin trulywildplants(thatis, thosethathave
sure onlyfromits relationship
withman (foran extendeddisestablishedrelationships
withanimalsotherthanman).
cussion,see Rindos n.d.). For example,certain varietiesof
Thereare twobasic modesin whichplantsadapt to theprobwheat currentlyundercultivationscattersome of theirseeds
lemsand opportunities
ofan animal-mediated
dispersalsystem.
withoutrequiringthreshing.
The rachisto whichthe seeds are
The firstand mostcommoninvolvesthe elaborationof an atattachedis said to be partiallydehiscent.Thus the seeds are
tractiveaccessorystructurefor consumptionby the animal.
capable of limiteddispersalwithoutthe intervention
of man.
The accessorystructureis “expendable”tissuewhichservesto
This is especiallysignificant
whenone considersthewidelyheld
attract the dispersalagent. The propaguleitselfis variously
beliefthat the indehiscentrachis is the hallmarkof domesti- protectedand carriedpassivelywith the accessorystructure.
cated grains.Likewise,in manyvarietiesofoats thereis a tenMany of the propaguleswhichwe call “fruits”representthis
dencyforthe ripe grain to shatter.This is a major problem, modeofadaptation.The fleshofthefruitservesto attractand
sinceit reducesthetotalyieldwhichcan be recoveredat harvest feedthe animal dispersalagent,whilethe actual reproductive
(see Schwanitz1966:34-35). Despite millenniaof interaction unitsare inedibleand are discarded,and thusdispersed,after
betweenman and thesecrops,”wild” characteristics
have not
thefruitis consumed.The seedsin stonefruitssuchas cherries
been completelyeliminated.In the same way, “natural” disand plumsand the corewhichcontainsthe seed in apples and
persal mechanismscharacterizemost of our cultivatedornapears are dispersedin thisway. The abundanceof feralapple
mentalplants and many of our vegetable,forage,and fruit trees growingin hedgerowsthroughoutthe northernUnited
crops (Schwanitz1966:96).
States and the feralpeaches of the southare evidenceof the
One way to understandthe great variationwhichmay be
effectiveness
ofthismodeofdispersal.
foundin cultivatedplantsis to lookto theevolutionary
tendenThe otherbasic mode of plant responseto potentialanimal
cies whichare favoredby varioustypesofinteractions
between distribution
agentsmaybe describedas aggregation.
It involves
man and plant.Perhapstheeasiestway to approachthisprobthe collectionof propagulesinto a largerstructure.Here the
lem is to considerthe interactions
fromthe perspectiveof the
propagulesthemselvesare consumed,and dispersaloccursdeorgansof theplant thatare utilizedby man. (These responses spitepartiallossesfromthetotalpropagulepopulation.The inare not restricted
to human-plantinteraction,
but are possibil- dehiscentrachisof the small grains,the ear of maize,and the
itiesin all herbivore-plant
interactions.)
Threemajorclassesof
heads producedby sorghumsmay all be seen as examplesof
plant organsmay be recognized:vegetativestructures,
repro- this type of attractiveaggregation.The developmentof large
ductivepropagules,4
and vegetativestructurespossessingsecseed massesin the New Worldcucurbitsis a further
example.
ondaryadaptationsas dispersalpropagules.
Accordingto Whitakerand Bemis (1975), theseplants were
In one type of herbivore-plant
interaction,the animal conoriginally
valuedfortheirseeds.Selectionforhighseed number,
sumes vegetative
structures
of the plant: roots,stems,petioles, and thusforlargerfruits,allows forsecondaryadaptationsby
leaves,and flowers.(Flowers,whilestrictlysexual organs,may
theplant.Anaccessorystructure-thefleshofthegourditselfbe consideredvegetativeorgans until the fruitripens.) The
becomesthemeansby whichtheplant attractsman. Even the
generalevolutionarytendencywhenan animal feedson these
indehiscentlegumeof the cultivatedbean may be seen as an
parts of a plant is towardsnonedibility;
the potentialforthe
example of this tendencytowardsaggregationin cultivated
developmentof a cultivationsymbiosisis ratherlimited.Typiplants. Aggregationand the developmentof accessorystruccal evolutionary
sequencesincludethedevelopment
ofchemical
turesmay be describedas responsesto thepredatorybehavior
defensessuch as poisons and tanninsand the elaborationof
ofanimals.Eithercan occurwithoutthepresenceofdeveloped
physical deterrentsagainst predation such as trichomes, agriculturalbehaviors.
sclerids,and thorns.Amongannual plants, a pressureexists
McKey (1975) has recentlyreviewedthe coevolutionof
towardsthe evolutionofprecociousflowering,
whichdecreases
tropicalfrugivorous
birdsand the plants on whichtheyfeed.
the timeduringwhichthe plant existsand thusis susceptible These plantshave adapted to specializeddispersalby a limited
to consumption.Anotherresponseof the plant is colonization numberof species of birds.Their fruitsare generallyhighin
proteinsand lipidsand thusprovidea verynutritiousdiet for
I A propaguleis any plant
the birdswhichfeedupon them.It is assumedthat the birds
organadapted to the sexual or vegetative reproductionof the motherplant.
provide the plant with a “higher-quality,
more ‘predictable’
Vol. 21
N 6 * December
No.
1980
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755
fixedifit is successfulin the
formis immediately
morphological
dispersal.”This seems reasonable,because only one or a few
is elimsymbiosis,since variationfromsexual recombination
species may feed on any plant. Thus dispersalbehaviorwill
show less variationthan the total set of dispersalbehaviors inated.
terms,the mostlikelyresponseof a
In generalevolutionary
exhibitedby all speciesofbirds.
The various morphologicalmodifications
exhibitedby the
plantlike thepotato to thepredatoryactivitiesofan animalis
ofsmalltuberswidelyspaced fromtheparenbirdsare interesting
in and of
fruitsdispersedby frugivorous
thedevelopment
themselves.They also show a type of adaptation which is
tal plant.Individualspossessinglargetuberslocatedcloseto the
of the evolutionof
motherplants would be undera negativeselectionpressure,
especiallyimportantforour understanding
predatorcouldeasilyretrievethem.If we
cultivatedplants. The fruitsdispersedby frugivorous
birds
sincea nondispersing
during
generallypossess morphologicalor biochemicalmodifications assumethatno plantingbehaviorby man was occurring
whichpreventdispersalsby birdswhichhave not coevolvedto
the early stages of potato utilization,it would seem that the
are most comfeed upon them.Morphologicalmodifications
“desirable”typesofpotato wouldexperiencea loweredchance
of the naturaldispersalsof wild
mon. Generallythe specializedfruitsare too large formost
ofsurvival.An understanding
the evolutionof the
birds of the tropicshave
birds to ingest.Many fruit-eating
potatoes could help us in understanding
possiblethatpotato tubers
cultivatedplant.It is theoretically
specializedguts whichare adapted to the handlingof these
fruits werealreadycoevolvedwithanotherdispersalagentand man
large fruits.Other types of specialized bird-dispersed
seedswhichare groundup in thegizzards
was able to “steal” the cropfromthatanimal.
produceintoxicating
The domesticationof the potato is furthercomplicatedby
of most otherbirds,producinga negativeexperienceto disof potato plants also occurs
of the fruits.Thus not onlydoes
the fact that sexual reproduction
couragefurther
consumption
whichencouragethe relation- withgreat frequencyin the regionto whichtheyare native.
coevolutioncause modifications
ship betweentheplant and its dispersalagent,but othermor- Most of the potatoes growingin the Andes set fruitsabunphologicaland chemical traits may develop which serve to
dantly.This may be more than a climatic response.Brush,
excludedispersalsby otherthanthecoevolvedagent.
Carney,and Huaman (1980) reportthatthepresenceofvolunteerand feralpotatoescontributesgreatlyto the diversityof
Certaintraitsof cultivatedplants havinga symbioticrelationshipwithman mayhave originally
arisen,and are certainly thepotato genepool in its nativehabitat.Fruitingabilitymay
selectionforthe trait,since fruitin part maintained,as means forthe exclusionof nonhuman be a resultof unintentional
dispersalagents.The largefruitsofthecultivatedapple,mango,
ing potatoesmay be morelikelyto colonizefields.This is beand peach are effective
meansforexcluding cause a seed willalmostcertainlybe overlooked,whilea tuber
pear, watermelon,
most dispersalagents otherthan man. Of course,birds may
willlikelybe harvestedand thusbe unavailableforgrowththe
peck at apples or stonefruits,but theyare generallyincapable
nextseason. Fruitingabilitymay also be a relicofthe original
of carryingoffthe fruitand thus actually dispersingit. The
domesticationof the crop. It is possiblethatpotatoesbearing
indehiscentrachis of the small grainsand the cob of maize
desirabletuberswere originallycarefullydug and that reproserveanalogousfunctions
in discouraging
nonhumandispersal duction of the desirable types occurredby the inadvertent
agents. As was implicitin my remarksabout the chemically plantingof the fruitsin disturbedgroundthat occurredas a
defendedfruitsof certainbird-dispersed
activity.Sinceconsiderabledisturbance
speciesof the tropics, resultoftheharvesting
a certainamountof outsideinterference
withthe systemmay
ofthesoiloccursduringthisprocess,thefruitwouldbe situated
occur,but overevolutionary
timeits effects
are minimal.Thus
in an ideal positionforfuturegrowth.Competitionfromother
it maybe seenthatcertaintraitsofthecultivatedplantare not
plants wouldalso be reducedbecause of thisdiggingactivity.
theevolutionof
in understanding
solelyforman’sbenefit,
butalso servetheplantin itsdispersals.
An additionalcomplication
The major evolutionaryeffectof thistypeof specializationin
cropslike the potato is the factthat theymay be reproduced
the relationship
betweenplant and animalis an intensification froma portionof the tuber.Thus, as in the case ofthe carrot,
of thesymbioticrelationship.
thediscardingofa sectionofthetubercouldallowforcolonizaall ofthecomplicaAn animal’s consumptionof asexual propagulesalso allows
tionofthecropin dumpheaps. Considering
investigation
foran adaptive responseon the part of theplant. Analysisof
tionspresentedby a croplike thepotato,further
this typeof symbiosis,however,presentsmoreproblemsthan
of the behaviorsof the plant in the wild and in its regionof
of
the analysisof the evolutionof domesticatedplants whoserecould do muchto advance our understanding
domestication
productivepropagulesare consumed.The firstissue which
domesticationas an evolutionaryprocess.Such investigation
ofthetypes
must be clarifiedis the distinctionbetweenreproductiveand
couldbe especiallyimportantforan understanding
storageorgans.The domesticationof crops such as manioc,
of selectivepressurewhichmay have existedbeforeplanting
turnips,and carrotsis best consideredwithinthe schemeprebehaviorsby man werewellestablished.
sentedearlierforthedomestication
ofplantsin whichthevegeIndependentsupportfora coevoluWeedsand domestication.
tativestructureis consumed.These plantsare not propagated tionaryviewofdomestication
may be foundin theexistenceof
by the structuresthat are generallyconsumed.However,the
weeds specificallyadapted to the conditionsof cultivation.
potentialof the top of the carrotor turnipto continuegrowth Weeds showmanyofthe traitsofcultivatedplantsdespitethe
and eventuallyproducea seed stalkcannotbe discounted.The
factthattheyare clearlynotbeingselectedconsciouslyby man
growingpoint of these roots is generallydiscarded (at least
forthesetraits.Weeds may be analyzedin thesame manneras
thattheyare “paratoday) in preparation.The discardingof thesevegetabletops
cultivatedplants,but withtherecognition
on a rubbishheap mightallow forseed productionand thus
sites” upon thehuman-plantsymbiosis.
colonizationofthearea by theplant.
Wickler(1968) gives several examplesof the evolutionof
Plantssuchas thepotato,in whichtheorganconsumedhas a
weeds under cultivation.He notes that the weed Camelina
natural dispersalfunction,are capable of developinga sym- sativahas divergedfromits nonweedancestorCamelinaglabra
bioticdispersalrelationship.
The gatheringof the tuberswith
by virtueof the selectiveprocessesoperatingin flaxfields.C.
The
subsequentinadvertentlosses wouldpermitthoseplants prosativais largerthanC. glabraand generallynonbranching.
to flaxleaves
resemblance
ducingthemostacceptablefoodto humansto spreadpreferen- leaves ofC. sativaalso bear a striking
tially.Since thepropagulesare asexual,and thusreproducethe
in both shape and color. Clearly,this resemblanceserves to
parentalphenotype,desiredcharacteristics
oftheplantswould
protecttheplant frombeingweededout of theflaxfields.The
to
be establishedin thecropmuchmorerapidlythanwhensexual
fruitof the weed is also indehiscentand requiresthreshing
propagulesare beingdispersed.Plantswhoseasexualpropagules separate the seed fromthe husk. While the seeds of C. sativa
are utilizedhave an advantage that is only approachedby
fromthoseofflaxin bothsize and weight,thecombination
differ
plants whose sexual propagulesare apomictic:any particular ofthesetwofactorsis such thattheycannotbe separatedfrom
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ANTHROPOLOGY
flaxseedsby winnowing.
C. sativais, in essence,a mimicof flax
Rindos:ORIGINS AND SPREAD OF AGRICULTURE
in bothvegetativeand dispersalphases ofitslifecycle.
In a similarmanner,theagriculturaltechniquesofman have
domestication
of certainfoodplants. Clearly,manymorefood
selectedstrainsof dodder (Cuscutaepilinum),whose mimicry plantsare available to man thanhave beendomesticated.Why
offlaxoccursonlyduringthedispersalstage.Weedystrainsof
should certain crops become domesticatedwhile other, apdodderproduce a double-seededfruitwhichapproximatesa
parentlyequally valuable crops remainwild? As a paradigm
flaxseed in size and weight.”Wild” strainsof doddercan be
forthisproblemI wouldliketo briefly
considertheacorn.
but the weedy
removedfromthe linseedcrop by winnowing,
Acornshave been used as botha stapleand a majoralternastrainsare dispersedwiththe crop.
tive source of food by many culturesthroughoutthe world.
Teosinte so mimicsthe vegetativestructureof maize that
While the acorn-basedculturesof the west coast of North
cannot distinguishbetweenthe plants
native agriculturalists
Americaare perhaps the best-known,
acorns have also been
untiltheflowering
stage.At thispoint,ofcourse,thelargesize
extensively
utilizedas humanfoodand as fodderin bothEurope
oftheplantand thelate stagein thegrowingcyclepresentgood
and theNear East. Indeed,it is likelythat theacornhas been
reasonsnot to botherremovingit; removalwouldbe pointless utilizedwhereverit is present.It is a large,conspicuousfood
or perhapseven damagingto adjacent maizeplantsbecause of
sourceand one thatneedsonlyminorprocessing(suchas leachrootdisturbance.Thus teosintehas adapted in sucha way that
ing) beforecooking.The acornsof certainspeciesof oaks are
man unintentionally
protectsit. Many believethat maize and
palatable withoutany processing.In manywaystheoak seems
teosintehave a commonevolutionaryhistory(Galinat 1974,
ideallysuitedto beingone of thebasic cropsofan agricultural
1975,Doggett1965,Mangelsdorf1974). If thisis thecase, then
civilization.
we mayviewthehistoryofthesetwoplantsas one ofdivergent
Since theoak has a longlifecycle,and thusa longtimemust
evolution.Two paths developedin a partiallysharedgenepool
pass betweengenerations,
it wouldseem thatit wouldbe diffiby adaptationto different
aspectsofthehuman-plant
relation- cultto domesticate:theresultsofselectionwouldbe too longin
ship.Both teosinteand maize have takenadvantageofman as
appearingto encouragefurtherconsciousselection.Othertree
a protectiveagent.As longas thecropwas an incidentaldomes- crops,however,suchas olives,thevarioustreefruits,
dates,and
ticate,man may have dispersedboth of them,but once maize
numerouspalms,have developedinto domesticatedplants debecame obligatelydispersedby man it was dispersedwithout spite theirlong life cycles. Anotherreason which mightbe
theteosinteportionofthegenepool. Thus themaizecob served
advanced for the oak’s nondomestication
is that, since it is
to allow maize to divergefromboth its originalhome and its
capable of providinga large and reliableharvest,thereis no
closest relative,teosinte.In the area in which teosintewas
reasonto select”improved”cultivatedforms.Yet, wildstands
incidentallydispersed,however,man continuedto protectit,
ofwheatsin theNear East are quiteas productiveas theolder
eventhoughtheintentoftheprotection,
at leastat a laterdate,
varietiesof wheat (Harlan 1967). Thus productivity
does not
was directedtowardsquitea different
plant.
seemto be necessarilya controlling
variable.
Isolationand domestication.
The divergenceof a cultivated
Within the contextof a coevolutionarymodel for plant
plant fromits wild ancestorrequireseffective
isolation.Introdomestication,
however,we may considerthe possibilitythat
gressionbetweenthe wild and the domesticatedpopulation
thenondomestication
oftheoak had littleto do withits potenwould continuallyoppose the developmentof the cultivated tial as a food source forman. Looking at the relationships
plant. Isolation throughthe activitiesof differing
dispersal already existingbetween oaks and otherpotentialdispersal
agentshas alreadybeenmentioned.
I wouldnowliketo consider agents in the environment,
we may hypothesizethat diverspatialisolation.In populationgeneticsthisprocessis generally genceof the oak intowildand cultivatedpopulationswas prereferred
to as allopatricspeciation.
ventedbypreexisting
coevolvedrelationships
betweenoaks and
Strongevidenceexists that certaincultivatedplants have
variousotheranimalssuch as squirrels.Squirrelsnot onlyharbecomedomesticatedoutsideof the regionto whichtheyare
vest acorns,but also plant them.We may call the planting
indigenous.Two examplesare the sunflower
and the tomato.
behaviorof squirrelshoardingand considerany plantingacThe sunflower
(Helianthusannuus) is almostcertainlya native
complishedmerelyincidental,but as faras thepropagationof
ofthewesternUnitedStatesand providedan importantsource
the oak is concernedthe distinctionis meaningless.It would
ofwildfoodto theearlyinhabitantsofthatregion.”It has been
have been verydifficult
forman to upsetthesquirrel’sagriculpostulatedthat,in time,thesunflower
becamea camp-following turalrelationship
withoaks. Furthermore,
it is hardto imagine
weedand was introduced
fromthewesternto thecentralUnited
a morphologicalchange in oaks that would exclude squirrels
States. Somewherein the latterarea the sunflower
appears to
fromfeedingupon the acornsand thus dispersingthe plants.
have been domesticatedand, as a domesticatedplant,was carWithoutexclusionof otherdispersalagents,domesticationdid
ried both eastwardsand to the southwest”(Heiser 1976:37).
not occur.
The tomatois apparentlydescendedfromwildspeciesofLycopersiconindigenousto theAndes.Yet withintheAndesthereis
no evidencethatthetomatowas knownas a domesticated
fruit. AGRICULTURAL
ORIGINS AND DISPERSALS
Instead,all of the evidence-linguistic,botanical,biochemical,
and historical–pointsto the area of domesticationfor the
INTRODUCTION TO THE MODEL
tomato as having been Central America and Mexico (Rick
1958, 1978).
Domestication,as viewedhere,is an evolutionary
processthat
Since in naturebothof thesecropsare stronglyoutcrossing, is the result of predator/preyinteractions.Domestication
spatial isolationofthecultivatedpopulationwas a prerequisite changesthemorphology,
oforganand distribution
physiology,
formorphological
divergence
ofthecropfromthewildancestor. isms.It resultsin a mutualism-a relationshipwhichbenefits
While the sunfloweris still stronglyoutcrossing,cultivated geneticallyunrelatedorganisms.It is, however,neitherinevistrainsof the tomatohave becomelargelyself-fertilizing.
This
The treatment
thatfollowsis proneto a
tablenororthogenetic.
enhancesthepotentialforthe evolutionof the cropas a cultifatalerrorin interpretation.
I shall be providinga modelfora
vated plant,since variationis greatlylimitedin self-fertilizing certainchangein subsistencepattern.The modelis a dynamic
plants.Self-fertilization
as a meansofisolationfordomesticated one and places great emphasison feedbackprocesses,but it
plants is extremelycommon;it may be seen, forexample,in
shouldnot be read to condonethe view that theprocess,once
peas, beans,peppers,and certainofthesmallgrains.
begun, must proceed inexorablyto certain ends. There are
Nondomestication.
Yet anotherindependent
sourceofsupport numerouswaysin whichtheprocessesleadingto domestication
forthecoevolutionary
modelforagricultural
originsis thenonand agriculture
may be subverted.
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757
In a
Likewise,thismodeldoes notpretendto be all-inclusive.
sense, I am tryingto followa particularthread of cultural
developmentsbackwardin time; I am not attemptingto describethefabric.Thus, muchofthevariationwhichmayoccur
Little
in humanculturesmustbe excludedfromconsideration.
attentioncan be givento societieswhichwereagriculturalor
domesticatory
at certaintimesbut laterabandonedthe behavior. Clearly,it would be extremelyusefuland interestingto
deal with such phenomena,but it would go far beyond the
boundsofthisessay.
Finally,we mustbeginto refinetheconceptofdomestication
advancedearlier.I have attemptedtoprovidean understanding
so
of whydomestication
occurs,but the view of donmestication
far presentedis so broad as to be, in the finalanalysis,uninteresting.
Coevolutionary
domestication
is a processthathas
occurredin almostall culturesat mostperiodsofhumanexiswith
tence.It gains its significancefromits interrelationship
agriculturalorigins.
In orderto appreciatetheroleofdomestication
inagricultural
origins,it is necessaryto anticipatesomeofthelaterarguments
and firstpresenta definitionfor agriculture:agricultureis
characterizedby an integratedset ofactivitieswhichaffectthe
environment
inhabitedby the domesticatedplant throughout
itslifecycle.As we shallsee,themajoreffect
is to
ofagriculture
forthe doincreasethe carryingcapacity of the environment
mesticatedplant, and this increasein plants and thus plant
has majoreffects
productivity
upon humanpopulations.
Agriculture
is a level or type of behavior.Like manyother
phenomena,it is frequently
easier to recognizethan to define.
To attemptto defineit solelyon thebasis ofa certaintechnique,
such as plowingor weeding,tendsto createa falseimpression
of the importanceof any particulartechniquewithinthe integrated schedule of activitiescomprisingagriculturalsubsistence.Frequentlythisleads us intobelievingthatculturessharinga particulartechnique,suchas theuse ofa diggingstick,or
evenparticularplants,suchas wheat,musttherefore
have had
a commonorigin.
of domestication.
is an outgrowth
Thus it is imAgriculture
to definea momentoftransition.
At an early
possiblerigorously
stagein thedevelopmentofagriculture,
it would be impossible
to identify
theprotoagricultural
confidently
society.The interactions with domesticatedplants of the early agricultural
fromthoseofthedomesticasocietywouldbe indistinguishable
matorysociety.The significant
techniquesof environmental
nipulationmightnotbe beingperformed
forconsciouslyagriculturalends.Firesencouraging
thegrowthofdomesticated
plants
mightbe beingset to drivegame;forestsmightbe beingcleared
to furnishbuildingmaterials.We could only be sure that we
wereindeeddealingwitha protoagricultural
societyifwe knew
howtherelationship
woulddevelopin thefuture.If we need to
define,for any particularsociety,the momentof transition
froma domesticatory
to an agriculturalway of life,I would
suggestthat it is the point at whichagriculturalinteractions
became more importantto the society than domesticatory
interactionswith plants. “Importance” may be read in two
ways.We may considerit to representtherelativesignificance
of agriculturalbehavior to the futuredevelopmentof the
thateach form
society.We mayalso viewit as thecontribution
of behaviormakes to the overallsubsistenceof the societyat
is of criticalimany givenmoment.This latterinterpretation
theevolutionand subsequentspread
portancein understanding
ofagriculturalbehavior.
0~~~~~~
Population
Solidline,totalfood;
relationship.
predator/prey
FIG. 1. The typical
broken
line,yieldper predator;a, pointat whichcompensatory
or all availableregions
behaviorof predatorbecomesineffective
ofpreyarefilled.
togrowth
favorable
betweenpredapredatordecrease.In a mutualisticrelationship
torand prey (fig.2), as the numberofpredatorsincreasesthe
totalamountofavailablefoodalso increases.The energeticcost
to thepreyinherentin providingsubsistenceto thepredatoris
compensatedforby actions of the predatorthat provide inforthe survivalor dispersalof the prey.
creasedopportunities
Seen in otherterms,mutualismsserveto increasethe carrying
forboththepredatorand theprey.
capacityoftheenvironment
The actionsof thepredatorwhichtendto increasethenumber
of the prey indirectlypermita greaternumberof predators.
Domesticationtendsto increasethe yieldofpreywithinthe
area inhabitedby thepredator.Ofcourse,thistendencywillnot
Numerousfactorsmay act to limitthe
continueindefinitely.
numberofpreyand thusofpredator.Eventuallythecompensaor all
tory behaviorof the predatorwill become ineffective
available regionsfavorableto the growthof the prey will becomefilled;thusthe yieldwilllevel offor even assumea negative slope. Yet thisstabilizationin yield,and thusin predator
numbers,is also subjectto change.Most ofthefactorslimiting
variablesand
thesuccessofthepreyspeciesare environmental
are thus external to the mutualisticrelationshipbetween
predatorand prey. Since few,if any, species are naturally
limitedin numbersby theirintrinsicrates of increase,any
will permitincreasesin the
“relaxation”of the environment
numbersof the prey species. Changes in the environment
for
directlyincreasethe carryingcapacity of the environment
permitgreaternumbersof predathepreyand thusindirectly
tors.
ofthepreyspeciesmay
The changethatleads to proliferation
/
__
~~~~~//
/
DOMESTICATORYRELATIONSHIPS
Predator/prey
i-nteraction.
Mutualisticrelationships
such as doPopulation
mesticationhave thepotentialto changetherelationship
which
existsbetweenpredatorand prey.In thetypicalpredator/prey FIG. 2. A mutualistic
Solid line,total
relationship.
predator/prey
relationship(fig.1), as the total numberofpredatorsincreases food;broken
change
ofeffective
b, moment
line,yieldperpredator;
ofthepreyspecies.
leadingto proliferation
both the total and relativeamountsof food available to the
758
CURRENT
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ANTHROPOLOGY
be a changein the morphology
ofthepreyor a modification
of
thebehaviorofitscoevolvedagent,includingchangein theway
theagentrelatesto the environment.
At a timebeforeagriculturalbehaviorswerewell established,changesin the morphologyofplantswereprobablyofmajorimportanceforthefurther
developmentof the human-plantrelationship.Traits such as
indehiscence,gigantism,and aggregationcould exclude previouslyeffective
dispersalagentsand thus allow fora greater
available yieldto humans.This changein theplants’ morphology would enhance the developmentof the human-plant
mutualism.
As we have just seen,the
Domesticates,
yield,and instability.
majoreffect
ofthemutualismbetweenmanand plantis greater
of the environment
forman. This increaseis not,
productivity
however,based on equal increasesin productivityof all componentsof the environment
(all potentialor actual preyspecies). Rather, a very small subset of potentialfood sources
providesall of the increasein productivity.As domestication
proceeds,so does man’s relianceupon an eversmallersubsetof
potentialfoodsources.Increasein theavailabilityofa resource
is accompaniedby a corresponding
increasein its utilization.
The effectof thisdietaryshiftis a reductionin theimportance
of nondomesticates.
This simplification
of the subsistencepatternhas majoreffects
upon its stability.
To understandtherelationship
betweenyieldand instability
in yield,we mayfirstconsidertherelationship
betweenmanand
any one domesticatedplant. The increasein yieldthat results
is onlythe averageincreaseovertime,that
fromdomestication
is, as the mutualisticrelationshipdevelops.Any given plant
whichis subjectto periodicand norgrowsin an environment
and its yield will vary about the mean from
mal fluctuation,
Thus the contribution
year to yearbecause of thisfluctuation.
of any particularspeciesofplant to the totalplant foodavailable to man will vary in responseto environmental
factors.
Whileaverageyieldis increasingovertimebecause oftheelaboration of coevolutionarydomesticationrelationships,the
absoluteyield at any given momentis a functionof specific
environmental
conditions.
beforethedevelopDuringtheearlystagesofdomestication,
mentof agriculturalsystems,this fluctuationin yield should
have littleeffecton the total yieldavailable to man. The contributionof any givendomesticatedplant to the total subsistence patternwill be relativelysmall. Membersof any given
domesticatedspeciesare likelyto be growingin any and all of
the locationswhichare conduciveto theirgrowth.Also, the
variousspeciesof plants withwhichman has establishedmutualisticrelationships
are likelyto be fairlyuniformly
distributed throughout
the environment,
no particularnichehaving
establisheditselfas the principal one for all domesticated
plants.Thus,whileenvironmental
fluctuation
willhave adverse
effectson the yieldof any particularspecies,the overallyield
will tend to remainreasonablyconstant.A bad year forone
plant is likelyto be a good yearforanotherplantgrowingin a
different
habitat;a bad yearforonespeciesis likelyto be a good
yearforanotherspecieswithdiffering
edaphicand physiological
This compensationin yield will permitproducrequirements.
tivityto remainrelativelystablefromyearto year,muchas it
does in any nondomesticatedecology.As we shall see, this
standsin starkcontrastto theinteraction
ofyieldand environmentwhichoccursin theagriculturalsetting.
AGRICULTURAL ORIGINS
tendencies.
The primaryeffectof agricultureon a
Evolutionary
ofthedependenceofthatsocietyon
societyis an intensification
domesticatedplants.Highlydevelopedagricultural
systemsare
based upona limitednumberofcultivatedplantswhichprovide
thebulk ofthesociety’sfood.Fromtheprecedingdiscussionit
should be clear that this tendencytowardsa decreasein the
number of niants nrovidinz subsistence is an ouutgrowth of the
Rindos:ORIGINS AND SPREAD OF AGRICULTURE
dynamicsof the mutualisticrelationship.There is a tendency
towards increase in yield and concomitantdecrease in the
numberofspeciesofdomesticatedplants providingthat yield.
places the major
It has also been notedthat the environment
limitationupon thedevelopmentofthisrelationship.
is composedof various niches forplant
Any environment
colonization.These nichesare welldefinedand relativelystable.
Thus the potentialnumberof places in whichany givenplant
oftheenvironby thecharacteristics
mightgrowis determined
ment. Clearly, any behavior by man that transcendsthese
on plantgrowthwillbe accompanied
limitations
environmental
by increasesin yield proportionalto the amount of “new”
nichespace. At the same time,any behaviorincreasingniche
size available forplant colonizationwillcause a corresponding
forman.
increasein the carryingcapacityof the environment
changeswhich
Any humanbehaviorcausingenvironmental
successof the domesticated
increasetheprobablereproductive
plant, and thus its yield,will have importanteffectson the
furtherevolutionof the domesticatedplant. Withinany locality,severaltendencieswill guidethe evolutionof the cultivated crop, among them (1) a reductionin diversity,both
geneticand phenotypic,(2) a tendencytowardsincreasedproAt thesame time,
and (3) autecologicalconvergence.
ductivity,
a seriesof tendencieswillbecomemanifestwithinthe total set
thedomesticatedecology,amongthem(1)
of cropscomprising
a tendencytowardsreductionin the numberof species on
whichman reliesforhis subsistence,(2) increasein total crop
As we shallsee, these
yields,and (3) autecologicalconvergence.
tendencieswill formthe basis forthe elaboration
interrelated
systems.
and dispersalofagricultural
antdyield.Changesin thedirectionofplant
diversity,
Systems,
modifiedecologyare
evolutionwithinthe early agriculturally
based on one rathersimplefactor:human agriculturaltechforplant growthand reproducnologycreatesan environment
is structurally
tion which, unlike the overall environment,
and temporallystable.
homogeneous
As numerousauthorshave observed,agriculturalsystems
ecologies:typicallythe agriculmay be describedas simplified
turalplant is a “weedyheliophyte,”that is, a colonizerof disturbed habitats, and the agriculturalfield or garden is an
in whichthe earlieststages of ecologicalsuccesenvironment
ofthiscolonizersystem
sionsare maintained.The predominance
foragricultureis based upon the factthat thereare numerous
ways in whicha disturbedhabitat can be createdby human
behavior.Fires,disturbanceofthesoil,theclearingofforestsor
the ringingof trees,and the creationof dump heaps are all
routesby whicha disturbed,and thus open, habitat may be
created. Early domesticatedplants preadaptedto this niche
evolutionintoagricultural
willthusbe favoredin theirfurther
plants.
Variousagriculturalbehaviorsserveto reducethe intensity
ofplantsthatare necesof naturalselectionforcharacteristics
saryforsurvivalin thewild.Irrigationreducesthenecessityfor
plantsto maintainmechanismsforsurvivalduringperiodically
droughts.Clearingof the land and weedingdecrease
recurring
the importanceof competitivemechanisms.Plantingencourages specificand uniformgerminationand seedlingphysioloultimatelyreducethevariagies.The techniquesofagriculture
tion to be foundin a speciesof domesticatedplant. Both the
wild and the early domesticatedplant had to maintainpleiotropicresponsesin the face of an unpredictableenvironment.
With a reductionin overall environmentalunpredictability
withinagriculturalsystems,thisvariabilityis no longerbeing
maintainedby naturalselection.Physiologicaland autecologiplantswithinany
also occursin all agricultural
cal convergence
givenlocality.As we shall see, thisdecreasein variabilityultimatelyyieldsan increasein vulnerability.
At thesame time,theselectionforhigheryieldsjust discussed
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759
will continueand even increase.Plants yieldingthe greatest
numberof propagules-thoseplants best adapted to the agricultural environment-willbe most likely to survive and
spread. The relaxationof selectionpressuresfortraitssuch as
willalso bringabout a new way forplants to
competitiveness
increasetheiryield. Energythat was previouslydivertedto
such tasks as protection,the manufactureof long internodes,
and the like may now be utilizedfor
perenniating
structures,
furtherincreasesin yield. Released fromthe requirementto
the plant whichputs energyinto the
possesssuch structures,
productionofpropaguleswillbe themostfitwithinan agriculturalsystem.
Processesanalogous to those occurringat the intraspecific
levelwillalso occurat theinterspecific
level.Those plantsbest
withinthe agricultural
adapted to survivaland reproduction
ecologywill come to dominatethe system.Given the homogeneityand stabilityintroducedintothe environment
by agriculturalbehavior,it is not unreasonableto expecta reduction
in species diversity-an increasingreliance upon fewerand
fewerspeciesto providethebasis forhumansubsistence.
thistendencytowardsuniAnotherfactorwillalso reinforce
of developingagriculturalsystems.
and simplification
formity
As a food source becomes more common,feedingon it will
increase.At firstthiswill be merelya functionof availability,
but as timepasses techniquesof productionand consumption
will tend to improve.Availabilityand efficiency
interactin a
positive-feedback
manner,and furtherspecializationis likely.
Specializationwillalso be encouragedby the localizationof
agriculturalproduction.Reductionof usage will decreasethe
probabilityoftheestablishment
ofcoevolutionary
relationships
betweenhumansand new species of plants. As more time is
man willcomeintoconspentin theagricultural
environment,
tact with fewerspecies of alternativefood sources. These
changes in time allocation, generallyknown as scheduling
changes,decreasetheimportanceofenterprises
competingwith
agriculture.Thus the establishmentof agriculturewithina
society will intensifyand direct tendenciesalready existing
underthedomesticatory
way oflife.
The development
ecologies.Agriculture
creates
of agricultural
a new type of climaxformation.The agriculturalfloratends
towardsstabilityas longas humanbehavioris interfering
with
othersuccessionalprocesses.Many ofthespecieswhichinhabit
the agriculturalclimaxare derivedfromplantsadapted to the
earliest,colonizing,stage of ecologicalsuccession.Agricultural
derivedfrom”weedy” plants that tend
staplesare frequently
to existonlyin newlydisturbedground.Anothercharacteristic
of manyof the staple cropsof agricultureis that theyare descendedfromplantsthatdid not alreadyhave mutualisticdispersal systemswithany animal otherthan man. The agriculturalflorais a climaxformation
composedofhighlyspecialized
colonizerspecies.Many oftheplantsare descendedfromancestorshavinggeophysicalmodesofdispersal;secondarymodificationsare adaptationsto human-mediated
dispersal.This striking combinationof geneticheritageand evolutionarysetting
and
goes farin helpingus to understandboththeproductivity
thelimitedspeciesdiversitytypicalofagricultural
systems.
Whiletheagricultural
ecologyis bothstableand simplecomparedwiththe overallecology,it nevertheless
willshowchange
overtime.Probablythemostimportantlong-term
changethat
occurs in agriculturalecologiesis the creationof new niches
withinthe ecology.As timepasses and plants respondto the
optionspresentedby the existenceof agriculturalareas, subdivisionof the existingspace will occur.This will permitthe
entryof new, not necessarilydomesticated,plants into the
ecology.For example,weedsmay evolveto utilizeagricultural
fieldsduringfallowperiodsand then begin to be subject to
manyof the same selectiveforcesexperiencedby the domesticates.
The changesthat occur in agriculturalecologiesover time
also allow us to understaind
the evolutionof weedinessand the
760
entryof “secondary”domesticatesintothe system.Weeds are
colonizersof thisnewagriculturalhabitatjust like agricultural
betweenthemis in theattitudeman
plants.The onlydifference
has towardsthem.Vavilov (1926), amongothers,has pointed
out that the distinctionbetweenweed and domesticateis at
besta tenuousone. Secondarydomesticatesare plantsthatare
capable of establishingthemselves,like weeds,in the agriculturalecologybut thatprovideman withusefulproducts.Prime
amongtheseare plantswhoseutilityis foundin theirvegetative
parts. Edible plantswhichcan establishthemselvesin the disturbedagriculturalecologyneed not developspecial coevolved
in orderto survive.Theyneedonlyscatter
meansofdistribution
theirseed. However,since theyare growingin the same environmentwith otherearly agriculturalplants, they will be
subject to the same selectionforhighpropaguleyield. They
will also exhibitthe same tendencytowardsedaphicand autcrop.The secas any otheragricultural
ecologicalconvergence
ondarydomesticatewill evolve subject to the same selective
pressuresas theprimarydomesticate:it is evolvingin thesame
environment.
The developmentof the agriculturalecologywill,because of
the interactionbetweenit and thegeneralecology,have major
effectson the divergenceof the cultivatedplant fromits progenitorspecies.While diversitywithinthe ecologicalniche is
likelyto be, at least initially,less than that outsideof it, the
of
resultwill neverthelessbe an increasein the heterogeneity
fordisthe entireregion.This will permitmoreopportunities
thedivergenceof
ruptiveselection(Thoday 1958) and intensify
the agriculturalplant fromthe early domesticatedplant. Human interactionwith the originallydomesticatedtaxon will
withtheagricultural
decreaseas theinteraction
plant develops.
Relaxationof the amountof interactionbetweenman and his
earliest domesticatedcrops will, in the presenceof highly
developed agriculturalsystems,leave the early domesticate
“stranded.”The humanagent withwhichit had developeda
coevolved dispersal or protectionsystemwill no longer be
is
as dispersalagentor protector,
and its extinction
functioning
to
almost inevitable.It is not surprisingthat it is so difficult
species” forso manyofour important
identifythe “progenitor
forextinction
have
agricultural
plants.Two majoropportunities
occurredin the historyof all primarydomesticates:(1) The
wild,uncoevolvedportionof theancestralgenepool mayhave
becomeextinctduringthe long timeperiodduringwhichcoevolutionarydomesticationoccurred.(2) The portionof the
genepool whichevolvedundertheconditionsofearlydomesticationmayhave becomeextinctduringtheperiodofintensified
evolutionwhich led to the developmentof the agricultural
plant.
DISPERSAL
OF AGRICULTURAL SYSTEMS
We have alreadynoted
andenvironmental
instability.
Agriculture
thatincreasinghumanrelianceon cultivatedplantsbringswith
it a relativedecreaseover timein the absolutenumberof taxa
producingthe major portionof the society’ssubsistence;that
fromyearto year;
taxa varyinproductivity
manydomesticated
thatconvergence
occursamongagricultural
crops;and that,by
limitationsupon the carrying
removingcertainenvironmental
fordomesticatedplants,agriculcapacity of the environment
increasein potentialyield
turalbehaviorpermitsa tremendous
and thus in potentialhumanpopulation.I would now like to
explorethe interactionof a contractingsubsistencebase, inan
crease in carryingcapacity,and variationin productivity,
have led to thespreadof
effects
interaction
whosedemographic
as a modeofhumansubsistence.
agriculture
We have discussedsomeof the consequencesof the developstableniche:thedivergence
mentofagriculture
as a temporally
the evoluof agriculturaldomesticatesfromtheirprogenitors,
tionofsecondarydomesticates,
and theevolutionofagricultural
weeds.Agricultural
ecologiesalso have locationalstability.The
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ANTHROPOLOGY
ofagricultural
concentration
plantsin limitedregionsincreases
yieldsby allowinga morecompleteharvest.At the same time,
it intensifies
thepotentialinstability
ofthesystem,and thishas
major effectsupon the demographyof the humanpopulation
dependentupon agriculturalproduction.Locational stability
intensifies
instabilityin severalways. Prime among themare
ofmicroenvironmental
and microclimatic
theeffects
variation.
A gardenarea thatoptimizesdrainageduringaverageyearswill
be too wet duringperiods of highprecipitationand too dry
duringperiodsof drought.Otherlocationaleffectsto be consideredlater includeconcentrationof resourcesand predation
and edaphiceffects.
Domesticatedand agricultural
plantsbringabout an increase
in thecarryingcapacityoftheenvironment
contributed
by domesticatedplants, hereafterreferredto as Kdom.5 While Kdom
tendsto increasegreatlyovertime,forreasonsoutlinedabove,
the changein Kdom is not alwayspositivefromone momentto
another.The components
oftheenvironment
showseasonaland
longer-term
variation. Climate, for example,is not uniform
fromyear to year, and over relativelyshortperiodsof time
differing
average climaticconditionswill prevail. Thus, yield
willvaryin responseto theseconditions.
In the later phases of nonagricultural
there
domestication,
willbe somevariationin productivity
overtime,but variability
is restrainedby severalfactors.As we have alreadynoted,the
early domesticatedplant is growingin a varietyof microenvironments.
Thus any climaticchangeneednotaffectall ofthe
microenvironments
in thesame way. For example,domesticates
growingin sitesthatare wetterthanoptimalwillprosperduring
a period of reducedprecipitation.Nonagricultural
domesticatorysocietiesalso tendto have a largernumberofspeciesconto Kdomthando agriculturalsocieties.Thus any given
tributing
changein the environment
is not likelyto affectall speciesof
domesticatesequally.Both oftheseintrinsic
factorswilltendto
reducetheeffects
ofchangesin theenvironment
on theproductivityofthedomesticatedecology.Perhapsthemostimportant
factorlimitingtheeffectsofchangesin Kdom, however,is external to thedomestication
symbiosis.The nonagricultural
society
is relyingupon domesticatedplants foronlypart of its total
foodsupply.Thus it is possible to compensatefordeclinesin
of the total
Kdom by increasedrelianceupon othercomponents
carryingcapacity (K). The failureof one domesticatedplant,
or of one domesticatedspecies of plants,will be compensated
for by increasedreliance upon other plants, both wild and
domesticated.
In a periodof earlyagriculture,
the varianceof Kdom willbe
greaterbecause of the evolutionof agriculturalecologies.The
evolutionof the cultivatedplant in the agriculturalenvironmentincreasesnotonlyyield,but also thesusceptibility
ofthat
yieldto environmentally
inducedcropfailure.The autecological
convergence
broughtabout by agricultural
selectionbringswith
it an increaseduniformity
in theresponseofagricultural
plants
to environmental
parameters.Thus a bad year forany given
memberof a cultivatedspeciesis likelyto be bad forall membersofthatspecies.And sincetheconvergence
is also occurring
between,as well as amongst,plant species,bad years forany
givenagriculturalstaple are likelyto be bad forotherstaples
also. Increase in productivity
has been boughtat the price of
in responseto the environment.
uniformity
to and intensifying
Contributing
the effectsof autecological
convergenceis the greaterlocational stabilityof agricultural
ecologies.Localization intensifies
the effectsof microclimatic
effectsupon total yield.To take an extremeexample,a hailstormjust beforethe harvestseason willhave vastlydifferent
effects
upona societyifit fallsuponthecultivatedfieldsthanif
it fallsin the woods. Since hail is frequently
a highlylocalized
5K is widelyused to stand for”carryingcapacity.” Kdommay thus
be read as ” that componentof K contributedby the yield of domesticatedplants.”
Rindos:ORIGINS AND SPREAD OF AGRICULTURE
phenomenon,the effectof hailstormsupon the total available
than it will be for
yieldwill be far greaterforagriculturalists
or a totallynondomesticatory
society.
eithera domesticatory
ecologiesincreases
Thus localizationofresourcesin agricultural
the possibilitythat all of the resourcemay be lost to a catastrophe.
Agriculturalsubsistenceis also accompaniedby a growing
specializationin diet.Thus a decreasein theyieldfroma staple
foodsupply,
cropwillhave majoreffectson the total perceived
and techas wellas theabsolutefoodsupply.Food preferences
niques of preparationwill have placed certainfoodsourcesin
positionsof prominence.Informationconcerningthe edibility
and processingof alternativefoodsuppliesmay be lost. Thus
decreasesin yield fromcultivatedplants may create the appearanceoffoodshortageeven thoughthe total available food
supplyin theregionmaynothave fallento thepointwhereit is
actuallylimitingsurvivalof the population.Animalsrespond
to theperceivedfoodsupply,not to some “objective” measure
of total available calories.
The increasedsusceptibilityof the
The basisfor instability.
agriculturalecologyto the extremesof normalclimaticvariamanipulation
tionmay be viewedas an effectofenvironmental
manipulation
itself.Many ofthesimplerformsofenvironmental
controlrelativelyconstant,predictableparametersof the enthe effects
of the
vironment.
They increaseKdom by mitigating
on the carryingcapacity of the enfundamentalrestrictions
vironmentforthe plant. Increasingcontrolover any limiting
bringswithit, however,an increase
aspect of the environment
in the vulnerabilityof the newlyheightenedKdom to those
leftunaffected
by controlbehaviors.
aspectsoftheenvironment
As we have seen, forexample,localizationof productionincreases Kdom and thus allows fora largernumberof human
of the systemto
beings,but it also increasesthe susceptibility
effects.The
negative microclimaticand microenvironmental
removalof any givenlimiton yieldallows other,uncontrolled
limitsto becomeevident.
Agriculturepermitspreviouslynonlimitingfactorsin the
of plants to expressthemselves.For
growthand productivity
fromdroughtwill not have major
example,a plant suffering
by minorinsectinfestalimitationplaced upon itsproductivity
tion. Correctionof the droughtconditionby irrigationwill
conallow forthe expressionof the limitationon productivity
tributedby the insectpredation.Thus techniquesof environto affectyield admental manipulationallow theenvironment
in newways.At any giventime,techniquesof environversely
mentalcontrolincreasethe negativeeffectsof conditionsthat
cannotbe controlledby the system.
new opportunities
also createsentirely
for limitaAgriculture
ofa crop,
The increasing
geneticuniformity
tionsonproductivity.
reductionin species diversity,edaphic and ecologicalchanges
of recreatedby agriculturalpractices,and the concentration
sourcesin a limitedarea all contributeto new potentialinstabilitiesin productivity.
of
increasesthe susceptibility
Increasinggeneticuniformity
in the prothe crop to attacks by pathogens.Polymorphisms
ductionofsecondarymetabolitesactingas biochemicaldefenses
discouragethe evolutionof specializedpathogens.A reduction
in thisdefensestrategyencouragesthe evolutionofpathogens
whichmayseriouslydamagea plantspecies(Feeny 1973).This
potentialsourceofdamageis especiallyclearwhenwe consider
crops in whichsecondarymetabolitesdistastefulto man also
serveto protecttheplantfromattackby otheranimals.
ecology
Reductionin speciesdiversitywithintheagricultural
upon the susceptimay in and of itselfhave importanteffects
bilityofthecropplant to pathogenattack.Escape frompredationmay be aided in manyplant communities
by the associaplants;the plants”hide” frompotential
tionofmanydifferent
predatorsby beinghard to findin the mosaicof diverseplant
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761
No
to changes in the carryingcapacity of an environment.
populationof animals is capable of instantaneouschange in
numbersresponseto changein the carryingcapacity.Instead,
nerability of crops to insect herbivores . . . may result from
plantingin monoculture
species whichhave evolved chemical
thepotentialpopulationmust”track”thechangesin thecarrydefensesappropriateto communitiesin which the optimum ing capacity. It will be somewhatout of phase with those
strategyis beinghard to find.”Competitionbetweenagricul- changesbecause oflags in reproduction
or behavioralresponse
turalcropswhichresultsin tendenciestowardsboth increased to perceivedchangesin theenvironment.
Changesovertimein
yield and reductionin species diversitythus may work to
Kdom willbe respondedto, in a delayedmanner,by changesin
counteractdefensesacquiredduringthe evolutionof theplant
the potentialpopulation.The average populationover long
in the wild.
to the effective
periodsoftime,however,willtendto correspond
The negativeeffectsof agriculturalpracticeson the land,
minimalcarryingcapacity(Kdom) (fig.3). Part of the potential
increasesinKdomcannot
amongthemerosionand changesin soilstructureand drainage humanpopulationproducedbyrecurring
patterns,are well documentedand will not be given further be maintainedduringperiodswhenKdomdropstoitslowestlevels.
here.Less well studiedare the effects
consideration
of agricul- We may view this componentof the populationas agricultural systemson the feedingpatternsof animals other than
turallyinduced “excess production”of people, hereafterreman. Agriculture,
especiallyin its later phases, may signifi- ferredto as Pd. The amplitudeofPd is clearlydetermined
by the
cantly alter the local ecologysimplyby the replacementof
interactionofa largenumberoffactors,includingthelengthof
areas ofwildvegetationwithcultivatedfields.This destruction a generation,
theamplitudeofKdom, therateof changeof Kdom,
ofwildhabitatscreatesfoodshortagesforanimalsthatrequire the availabilityof alternativefood sources,and the way in
plants growingin thesehabitats.Thus theymay turn,out of
whichchangesin Kdom are tracked.Nevertheless,forour purnecessity,to feedinguponagricultural
crops,eventhoughthese
by the interactionof Kdom and
poses treatingPd as determined
plantsmaynotprovidefavoredsourcesoffood.
heuristicvalue.
Kdom has considerable
Finally,theincreasingconcentration
ofresourcesencourages
of the demographiceffectsof
Figure 3 is an interpretation
predation.The sameconcentration
ofresourceswhichfacilitates agriculturalinstabilitytakinginto account the trackingbehaharvestofthecropby humanswillfacilitateitsharvestby nonand
viorof humanpopulations.The hypothetical
productivity
humanpredators.And whileman may delay consumptionof
resultantdemographic
by thisgraphreprechangesrepresented
theplant to optimizeharvest,mostof thesepredatorswillnot
sentconditionssuch as mighthave existedin an earlypristine
be underthe same restraints.Thus theymay attack the field agriculturalsociety.Here we may note an averageincreasein
beforethe cropripens.They may also be capable ofutilizinga
minimalKdom
and theeffective
Kdom, thepotentialpopulations,
crop at a period duringits life cycle whenit cannot be con(Kdom). The graphalso showsthreepoints(a, b, and c) at which
sumedby man,forexample,duringearlyseedlingor vegetative the actual populationis greaterthan can be maintained.We
stages.Thus loss of the total crop may occurbeforeany yield
excessproductionof
mustconsiderthefateof thistemporarily
has been givento man.
thefactor
humanbeings.In essence,we are seekingto identify
The fundamentalcause of agriculturalinstabilityis agricul- which acts to reduce the populationin a particularlocality
tureitself.All ofthenewadverseeffects
whichtheenvironment whenan environmental
crisiscauses a suddendeclinein Kdommay have on agriculturalproductivity
are inducedby agriculThe most frequentresponseof any animal populationto a
turalpractices.Yet at thesame timeagricultureis responsible dropin thecarryingcapacityis emigration.
Emigration(rather
forgreatlyincreasedaverage yield and thus permitsgreatly than starvationor declinein per capita consumption)is espeelevatedhumanpopulationlevels.Overthelongterm,it would
ciallylikelyif onlyone componentof the carryingcapacity is
seemjustifiedto say that,despitethegreaterinstability
ofagrisuddenlyreduced.Part of the animalpopulationwillleave the
culturalproduction,this increasein populationlevels is eviarea in search of a place wherethe limitingresourceis more
dence of “progress.”
abundant.
However,the increasesin populationwhichaccompanyincreasesin Kdomoverlongperiodsoftimeare “successes”forthe
systemonlyatthemoment
ofchange.The agriculturally
enhanced
populationlevels now requirecontinuallyelevated levels of
productionfortheirmaintenance.Further,overrelativelyshort
periodsoftime,theenhancedpopulationlevelbecomesnothing
morethan the “normal”populationlevel. Thus the increases
in productivity
broughtabout by agricultureare absorbedby
a growingpopulation.Increasinglysophisticatedtechniquesof
environmental
manipulationare requiredforthe maintenance
of the same rate of growthand, because of increasinginstability, oftenfor maintenanceof the same level of population.
Human populationsgrowin proportionto the effectiveness
of
in raisingthe carryingcapacityof theenvironment
agriculture
forman. Yet, the moreeffective
agriculturalproceduresare in
reducingenvironmentallimitationsupon the productivityof
y
metiatdplnt Kdm) igte old in,miimmefeciea/
theagriculturalecology,themorelikelytheyare to createnew
lat
dmetiatd
nirnmntcotrbuedb
in
cpait
o
te
opportunitiesfor failuresof the system.And as agriculture
idiat “exes” oplaio
(Kom; roenlie,poultin.Arow
createshigherand higherpopulationlevels,the effecton the
(Pd)
.~
~
~~~~
societyof the failuresof the systemwill becomeincreasingly
tragic. Successfulagriculturalsystems require increasingly
Timeabc
successfultechniquesofenvironmental
manipulationmerelyto
maintainthe statusquo.
andpopulation.
between
FIG. 3. The relationship
Heavy
productivitv
Instabilityand dispersal.The interactionof increasein pro4iicrg
ptfevn
t
tbd/
ductivityand increasein instabilityof productivity
has been
responsiblefor the tremendousspread of agriculturaltechniques.To understandthissomewhatparadoxicalsituation,it is
species (Tahvanainen and Root 1972). As noted by Feeny
to speculateas to whetherthevul(1973:14), “It is interesting
necessarv to u,nderstand] how anv
762
animal
nonaio,T1cn
resnonAs
CURRENT
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ANTHROPOLOGY
a declinein foodsupplymaybe expectHumansexperiencing
ed to respondin the same manner.A dropin Kd,,, willencourage part ofthepopulationto leave and establishitselfin a new
area. A slowdeclinein relativeproductivity
suchas thatoccurringat Pointa maybe due to ecologicalor edaphicdegradation
becauseofagricultural
occurring
practices.Whilelargechanges
in populationwill not necessarilyoccur,groupsmay leave in
in whichto farm.Suddenand
searchof “better”environments
drasticdeclinesin relativeproductivity
such as are shownat
Pointsb and c willalso cause emigration.
In thesecases we may
assumethatemigration
willbe encouragedby anotherfactorin
additionto thesearchfora “better”agriculturalenvironment.
If a drasticdrop in production(a famineor a sudden great
scarcityofcultivatedfoods)occurs,it is likelythatthepopulation will returnto the exploitationof nondomesticated
food
sources.We have alreadynotedthatthefamineneed notbe an
“objective”lack ofpotentialcaloriesin orderto be perceivedas
one by thepopulation.However,sincean agriculturaleconomy
can supporthigherpopulationlevelsthana gathering
economy,
and since at least certainnonagricultural
domesticateshave
beenlost,partofthepopulationwillbe forcedintonewareas in
searchofwildresources.Thus a declinein Kdomwillbe especially
noticeable to an agriculturalpopulation because of several
interrelated
factors:higherpopulationlevelsin any givenarea,
losses of wild food sourcesand nonagricultural
domesticates,
and changesin theperceptionofwhatconstitutes
foodscarcity.
The onlyotherlikelyand effective
responseofa societyto a
dropin K(iomis increaseddemandforenvironmental
control.If
this occurs,however,it may simplybe incorporatedinto the
graph by increasingthe amplitudeof the Kdom curve.In this
modelincreasesin productivity
alreadyincorporatetechniques
of environmental
control;thus theycannotbe reenteredas a
newvariable.Also,as has been stressed,environmental
control
is intimatelytiedup withinstabilityin yield;decreasesin Kdom
are inevitableeffectsof an agriculturalsystemexistingin a
variable and evolvingenvironment.At best, environmental
manipulation
willdelaytheneedofthesocietyto finda solution
to theproblemof theexcesspopulationinducedby theperiods
of “successful”agriculturalproduction.
It is importantto recognizethat theseemigrantgroupswill
probablytake withtheman agriculturaltradition;theinstability created by agriculturalsubsistencewill bringabout the
spreadofthesystem.Besides theconservatism
inherentin any
society,anotherfactorfacilitatestheemigration
ofagricultural
populationswithoutloss of agriculturaltechnology.The environmentalcontrolsinherentin agriculturalbehaviorpermit
easy colonizationof new regions.Emigrantgroupsfrommost
societiesrequirea definableset of preexisting
nonagricultural
conditionsiftheyare to maintaintheirmodeofsubsistence.Of
course,agriculturalsocietiesrequiredefiniteecologicalconditionsalso, but the relativelyslow spreadof agriculturalsocieties, such as posited here,will allow time foradaptation by
crops to gradientsin the environment.
Secondarydomesticationwillpermitcolonizationof the fieldsand gardensby new,
better-adaptedplants,and eventuallya wholenew ecological
zone may open up to theagriculturalist.
We mightalso briefly
note that whilethe activitiesof most nonagricultural
peoples
do not interferewith subsequentutilizationof the land by
agriculturalists,
theconverseis farfromtrue.
DISPERSAL
AND INNOVATION
Domesticatory
and agricultural
systems.
We may summarizethe
last sectionby sayingthatthedynamicinteraction
betweenan
increasingKdomand thePd places theagriculturalsocietyat an
advantagerelativeto societieswithothermodesofsubsistence
in termsofpotentialforgrowthand dispersal.Agriculture,
by
inducingenvironmental
instability,creates the conditionsfavorableforits ownspread: theenvironmental
controlinherent
Rindos:ORIGINS AND SPREAD OF AGRICULTURE
notonlyspawnsnewpopulationsand sendsthem
in agriculture
but also allows themto continuein
offintonewenvironments,
the same subsistencepattern.
manipulation
The close connectionbetweenenvironmental
and instabilitiesin productionwas of majorimportancein the
evolutionof domesticatoryinteractionsinto genuineagricultural systems.Clearly,agriculturedid not springfullydevelopedfromthethighofculture.The earliesttypesofagricultural
parts of existingsubsistence
techniqueswere well-integrated
strategies.Activitiesthat were performedfor other reasons
The
on the local environment.
could not help but have effects
the
importanceoftheclearingofbrushforshelterconstruction,
destructionof trees for defensiveor economicreasons, the
burningofgrasslandsas an aid to hunting,theselectivepreserusefulplant or tree,and the creation
vationofan immediately
ofdumpheaps nearhumanhabitationsfortheevolutionof the
techniquesof earlyagriculturalsystemshas been discussedat
lengthin the literature.Preciselyhow theseactivitiesbrought
about the transitionto a totallyagriculturalway of life has
been less than clear. Especially confusingis the recognition
thatmanyofthetechniquesmaybe knownto man withouthis
necessarilyutilizingthemin a subsistencesystem.The model
thus far developedfor the originand spread of agricultural
systemsmay be extended,with certain qualification,to an
interactionsevolvedinto
of how domesticatory
understanding
agriculturalsystems.
We mayfirstconsidera nullcase: A giventechniqueincreases
fortheearlydomestithecarryingcapacityoftheenvironment
an increasein
cated plant (increasesKdwn)). There is therefore
humanpopulationin the area. However,if onlythe carrying
capacityof the regionforhumanswereto rise-that is, ifnow
the same area could supporta greaternumberof humanstheinitial
populationnumberswouldremainconstantfollowing
resultantfromthis
increase.However,the”culturalfecundity”
change in techniquewould be extremelylow. If emigration
capacity,thenemigrawerea fixedproportionof reproductive
tionwouldonlyincreasein directproportionto the increasein
population.If emigrationwere the resultof extrinsicfactors,
rateswouldremainunchanged.If,however,another
emigration
formof behaviorwere to increaseboth carryingcapacityand
ofthecarryingcapacity,we couldpositthesame
theinstability
sequence of eventsas in the dispersalof agriculturalpopulations.We have spokenof the “success” attendantupon techWe maynowmodifythe
manipulation.
niquesofenvironmental
conceptof successto includethe probabilitythat certaintypes
willprovidethecause of theirown dispersal.We may
ofactivity
potential”of a
even speak, allegorically,of the “reproductive
societypracticinga givenformofbehavior.The greatestreproductivepotentialwould arise when the relationshipbetween
productivity(Kdom)and instability(expressedas Pd) is such
that the emigrantpopulation,over time,wouldbe maximized.
Theoretically,an increasein the reproductivepotentialof a
societycould come about withoutincreasein absoluteproductivityifan increasein instabilityalone wereto occur.It seems
unlikelythat thiswouldhave happenedin the developmentof
because ofthepressures,
alreadydiscussed,towards
agriculture
domestithe natural selectionof continuallyhigher-yielding
cated plants,but it shouldbe recognizedas a possibility.
We may restatethis insightby notingthat those systems
Pd is thedirect
whichmaximizePd willspreadmostsuccessfully.
expressionof the interactionof Kdom and Kdom. Thus, fromthe
behaviorswereappearing,
veryfirststagesin whichagricultural
of unstablesystemswas
a tendencytowardsthe proliferation
evident.Of course,thisis not to claim that Kdom, the average
It is probably
ofa system,is totallyunimportant.
productivity
at least today,whereperiodicshortagesin
highlysignificant,
one area are at least potentiallyamenableto solutionby the
importof food fromotheragriculturalregions.However,the
Vol 21 * No. 6 * December1980
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763
ofKdomintoa modelforagricultural
incorporation
originsseems
inappropriate.
Theslowevolution
ofdomesticatory
systems.
Perhapsthegreatest anomalyforthoseacceptingthe revolutionary
viewofagriculturaloriginsis the observationin the archaeologicalrecord
thatwell-domesticated
plantsare foundin eventhemostprimitiveagriculturalcontexts.This is not in keepingwiththe view
that earlyagriculturaltechniquesprovidedthe selectiveforces
whichtransformed
thewildplant intothedomesticate.If agriculturaltechniquesarose beforethe domesticatedplant, we
wouldexpectto findnumerousintermediary
formsshowingthe
selectivepowerof agriculturaltechniqueson the evolutionof
the domesticatedplant. Anotherhighlyconfusingissue for
thosebelievingin a few”centers”of agriculturaloriginis the
existenceofnumerousspeciesofplantsthatseemto have independentlyenteredagriculturalsystemsovervast areas.
Both of theseproblemsare solvedif we accept the coevolutionaryinterpretation
of the evolutionof the domesticated
plant. As we have noted,domesticatory
systems,especiallyto
the extentthat theyare developinginto agriculturalsystems,
will disperseinto new areas by means of the same instability
maximizationprocessesjust discussed.This dispersalwill be
accompaniedby opportunities
fortheevolutionand acquisition
ofnewdomesticates.
New domesticatesmayevolve domesticationsymbiosiswithmanas he movesintonewareas. Also,since
human-coevolved
plants are not culturallybound,the movement of already coevolved domesticatesbetween coexisting
domesticatory
societieswillbe easy. This will…
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