The Ecology of Social Transitions in Human Evolution Author(S): Robert Foley and Clive Gamble Source: Philosophical Transactions: Biological Sciences, Vol
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The Ecology of Social Transitions in Human Evolution Author(s): Robert Foley and Clive Gamble Source: Philosophical Transactions: Biological Sciences, Vol. 364, No. 1533, The Evolution of Society (Nov. 12, 2009), pp. 3267-3279 Published by: The Royal Society Stable URL: http://www.jstor.org/stable/40485787 . Accessed: 13/02/2014 04:17 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The Royal Society is collaborating with JSTOR to digitize, preserve and extend access to Philosophical Transactions: Biological Sciences. http://www.jstor.org This content downloaded from 144.173.6.145 on Thu, 13 Feb 2014 04:17:41 AM All use subject to JSTOR Terms and Conditions PHILOSOPHICAL TRANSACTIONS OF T> PM. Trans.R. Soc. B 364,3267-3279 THE ROYAL1^ (2009) SOCIETY JLß doi:10.1098/rstb.2009.0136 The ecology of social transitions in human evolution Robert Foley1* and Clive Gamble2 1LeverhulmeCentre for Human EvolutionaryStudies, University of Cambridge, Fitzwilliam Street, Cambridge,Cambridgeshire CB2 1QH, UK 2 Departmentof Geography,Royal Holloway, Egham, Surrey, UK We knowthat there are fundamentaldifferences between humans and livingapes, and also between livinghumans and theirextinct relatives. It is also probablythe case thatthe most significantand divergentof these differencesrelate to our social behaviourand its underlyingcognition, as much as to fundamentaldifferences in physiology,biochemistry or anatomy.In thispaper, we firstattempt to demarcatewhat are theprincipal differences between human and othersocieties in termsof social structure,organization and relationships,so that we can identifywhat derived featuresrequire explanation.We then considerthe evidence of the archaeologicaland fossilrecord, to determine the mostprobable context in timeand taxonomy,of these evolutionarytrends. Finally, we attempt to link fivemajor transitionalpoints in homininevolution to the selectivecontext in which they occurred,and to use the principlesof behaviouralecology to understandtheir ecological basis. Criticalchanges in human social organizationrelate to the developmentof a largerscale of fission and fusion;the developmentof a greaterdegree of nestedsubstructures within the human commu- nity;and the developmentof intercommunitynetworks. The underlyingmodel thatwe develop is thatthe evolutionof 'human society'is underpinnedby ecologicalfactors, but these are influenced as much by technologicaland behaviouralinnovations as externalenvironmental change. Keywords: human evolution;social structure;social evolution;hominin behaviour; technologicalevolution 1. INTRODUCTION 1991) to life history(Charnov & Berigan 1993) to The evolutionary,or Darwinian,study of societyhas a the threatof prédation(Van Schaik & Hörstermann long and oftencontroversial history, encompassing as 1994) to the costs of territorialdefence (Lowen & it does the early days of social Darwinism and the Dunbar 1994). Key to all of these, however,is the sociobiological debate of the 1970s (Wilson 1975; general consensus that social structureis shaped by Allen 1976). A numberof thingshave perhaps made resources.The principlesof socioecologyprovide a this a less contentioustopic than it was. Of these, powerfulframework for studyingsocial evolution, the most importantis the fact that the phrase 'The and provide the basis for the main thrustof this Evolutionof Society' is no longer synonymouswith paper- 'thatthe major patternsof human social evol- the evolutionof human society.A centuryof research utionhave been shaped by changesin the environment in animal behaviour has extended the social world or changes in the ecological relationshipsbetween well beyond humans (Wilson 1975; Trivers 1985; humans and their resources,which can be tracked Runcimanet ah 1996). Social animals can be found throughtime'. across all the major groups (Vos & Velicer2006). As we shall argue, over the course of human In the firstpart of thispaper, we will considerwhat evolution,changes in male foragingbehaviour have some of these key generalsocial traitsmight be, as a led to them havingincreased control over resources, basis for consideringtheir evolutionaryhistory and and influencingthe distributionand behaviour of role.In otherwords, 'what distinguishes human society, females. This shiftrepresents not just a change in fromthat of other animals, particularly, given the recency socioecology,but also in the underlyingmodel of of the last common ancestor,from chimpanzees (Pan behaviouralecology, and may be one way in which troglodytes)andbonobos (Pan paniscus)?. we can understandthe unique natureof human society Additionally,advances have come in understanding (figure1). the principlesunderlying variation in social behaviour (Crook 1970; Krebs & Davies 1984). Such principles range from the costs and benefits of cooperation 2. BASAL HOMININSOCIALITY (Clutton-Brock 1991), parental certainty (Davies At the most basic level, the parametersdescribing human society are the same as those for any other vertebrategroup. The mostobvious of these is theten- * Authorfor correspondence ([email protected]). dencyto be social itself,namely to livein groupsmade One contributionof 16 to a Discussion Meeting Issue 'The up of known individuals(Hinde 1983). Other basic evolutionof society'. parameters that appear to be common across 3267 This journalis © 2009 The Royal Society This content downloaded from 144.173.6.145 on Thu, 13 Feb 2014 04:17:41 AM All use subject to JSTOR Terms and Conditions 3268 R. Foley & C. Gamble Social transitionsin humanevolution r igure 1. 1 he classical model ot socioecology,in whichowing to the dînèrentcosts ol male and temalereproduction, témales are more stronglyinfluenced by resources,and males by the distributionof females(Wrangham 1980). During the course of humansocial evolution,the increasedability of males to controlresources has led to a closureof the cascade model,with males exertingcontrol over female distribution through the controlover resources. humansand non-humansare moreprolonged parental socioecologyof chimpanzees,and presumedhere for relationships,which might be eithersex or both, kin- the earliesthominins, would be the occurrenceof a based relationshipsamong residentadults, sex-based level of daily fissionand fusionin foragingactivities, patternsof dispersal,more or less prolongedrelation- with smaller parties formingthe activitygroups. ships between adult males and females,with one or Daily fusionwould occur in the contextof sleeping more partners, some degree of tolerance of the trees/shelter. presence of othermembers of the 'society',a lack of equivalent tolerance for members of another group (or at least a differentpattern of behaviour) and 3. DERIVED HUMAN SOCIAL PATTERNS some degreeof structuredor repeatedstyle of relation- Derived human traits can be divided into three shipbetween individuals (e.g. dominance,submission, categories- those that show little structuralchange friendliness,aggression, etc.). and essential continuityfrom the basal hominin/last At this level, these basic parametersmay be con- common ancestor,even if theyhave been elaborated sideredeither as plesiomorphictraits that have evolved (column B); those that are similar in form to the deep in vertebratehistory or as formsof homoplasy ancestralcondition, but have changed significantlyin commonto all social animals.By lookingmore specifi- quantitativeterms (column C); and those thatappear cally at apes, especiallythe chimpanzee/bonoboas a to be derived featuresthat are more or less novel sisterclade, we can identifya number of basal traits (column D). It is clear that a number of key traits which it is reasonable to assume were presentin the develop duringthe course of human evolution,which earliesthominins. alterthe fundamentalstructure of society.In practice, Althoughit has been criticized(Sayers & Lovejoy these are underpinnedby unique mechanismsassoci- 2008), the genus Pan servesas the most parsimonious ated withhuman culturalcapacities, but, at a socioeco- basis for determiningbasal hominin social traits logicallevel, these are propertiesfound elsewhere in the (table 1, column A). The assumptionhere is thatthe animal kingdom,and thereforecan be consideredto earliest hominins lived in multi-male,multi-female have evolved as behavioural traits in response to 'communities',and this is the fundamentalunit of resource-basedconditions - the massiveextension of a humansocial organization(Ghiglieri 1987; Wrangham fission-fusion system(elephants, Loxodonta africana) 1987; Foley 1989). This is important,as much theo- (Couzin 2006); much greatersubstructuring within rizing in anthropologyhas tended to place primacy multi-male, multi-femalecommunities (hamadryas on the familyunit, but we see this as a trait that baboons, Papio hamadryas)(Kummer 1968); strong emergesduring the course of our evolution.On the and persistentmale-female relationships (many birds, basis of comparisonwith the apes more widely,it is forexample) (Mock & Fujioka 1990); higherlevels of also probable thatmale residenceand femaletransfer paternalinvestment (primates, many birds) (Charpen- was the primaryorganizational