TREE vol. 5, no. 1, January 1990

hthhto be the targets of host immune re- 1 Rice, R.H. and Green, H. (1977) Cell 18, 6 Tseng, H. and Green, H. (1989) Mol. sponses, it is possible that some are 681-694 Biol. Evol. 6,460-468 subject to selection favoring diversity i7y-;;;, M. and Green, H. (1985) Cell 40, 7 Dijan, P. and Green, H. (1989) Mol. as a means of avoiding immune rec- Biol. Evol. 6,469-477

ognition. Data from systems like the 3 Eckert, R.L. and Green, H. (1986) Cell 8 Teumer, J. and Green, H. (1989) Proc.

primate involucrin genes may pro- 46,583-589 Nat/ Acad. Sci. USA 86,1283-l 286

vide a valuable baseline for testing 4 Parenteau, N.L., Eckert, R.L. and Rice, 9 Nei, M., Stephens, J.C. and Saitou, N.

(1985) Mol. Biol. Evol. 2, 66-85 the hypothesis of positive selection

R.H. (1987) Proc. NatlAcad. Sci. USA 84, 7571-7575 10 Weber, J.L. (1988) Exp. far&to/. 66,

in cases of this sort. 5 Tseng, H. and Green, H. (1988) Cell 54, 143-170

A New Society for the Study of Human Behaviour and Evolution Monique Borgerhoff Mulder

STUDY OF HUMAN BEHAVIOUR in the light of evolutionary theory has grown in a number of disciplines since the 1970s. Anthropologists were among the first to take up Wilson’s chal- lenge’, seeking to determine how cul- tural diversity in traditional societies can be studied as a branch of behavioural ecology*. Psychologists turned to the predispositions and propensities whereby individuals ap- pear to select behavioural strategies appropriate to their sex and circum- stances3. By the mid 198Os, psy- chiatrists had begun to explore the possible evolutionary origins of emotion and neurosis4, and phil- osophers were contemplating how a history of individual selection might influence the study of ethics and epistemology5. Even economists, lawyers, historians, political scien- tists and sociologists were using a darwinian slant to tackle problems such as reciprocity, morality, law and social stratification, and a few biologists wrestled with sexual di- morphism, rape and sperm compe- tition in humans.

The Human Behavior and Evol- ution Society (HBES) was launched in late 1988 to provide a forum for the exchange of ideas and research find- ings amongst these people. The so- ciety’s first annual meeting was held at Northwestern University, Illinois, USA, organized by Nancy Bert& Laura Betzig, William Irons and Paul Turke, and was attended by 200 people.

In a field in which evolutionary speculation runs rife, the most cheer- ing aspect of many of the sessions was the ever-increasing emphasis on

Monique Borgerhoff Mulder is at the Dept of Anthropology, University of California, Davis, CA 95616, USA.

4

empirical data and the more care- ful exploration of hypotheses. For example, in examining whether pos- itions of political or social importance can be exploited for reproductive ad- vantage6, investigators have moved on from simple correlational studies. Looking at the reproductive per- quisites of political power in the USA, Gary Johnson (Lake Superior State University) found that defeated Presi- dential candidates had more children and grandchildren than their success- ful contestants, at least in the pre- Civil War period. Further analyses in- dicated that candidates .with fewer children at the time of their election were more likely to be chosen as presidents. This study was notable in that it used appropriate comparison groups, and explored causality in the relationship between an individual’s political and reproductive careers. With this kind of approach, evolution- ary hypotheses may lead us to look at aspects of human behaviour and psyche not previously investigated.

The new interdisciplinary field that constitutes HBES is driven by the ex- citement of tackling simultaneously the four central questions of ethol- ogy’: what are the physiological mechanisms underlying any given behaviour pattern, what is its survival (or fitness) value, how is it learned during development, and what is its phylogenetic history? Sociologists, economists and demographers pur- sue the study of mechanism and function, psychologists and psy- chiatrists investigate motivation and development, and anthropologists and historians use the comparative method to explore phylogeny and function. Inevitably, some problems arise with this ambitious project: function, mechanism and develop- ment are rarely studied in the same population. For instance, do the mate

preferences expressed by US col- lege students, uncovered in a careful questionnaire study by David Buss and David Schmitt (Michigan), help us to understand the intriguing age- dependent adaptive marital choices of 18th and 19th century Krummhorn women examined by Eckart Voland (Gottingen)? The answer is of course ‘No’, and yet the tendency to over- generalize findings from one context to another dies hard. At the con- ference, more fruitful dialogue be- tween investigators studying differ- ent levels of analysis might have been achieved had not sessions been concurrently run.

Despite widespread enthusiasm with both the conference and the new interdisciplinary field, there are some troubling developments. The first is the absence of paleoanthropologists. A large proportion of the conference presentations relied on the assump- tion that normal or psychotic be- haviours exhibited in populations, both modern and traditional, are re- sults of selective pressures on the human psyche during earlier stages of our evolution, for which vague terms such as ‘the environment of evolutionary adaptedness’ or even ‘yester-year’ are employed. Given how little we know of such selective pressures, and how variable they might have beer?, such paleo- agnosticism is deplorable, and fos- ters wild evolutionary handwaving.

The second development is even more worrisome: an explicit and re- peated recommendation by several speakers against criticism of each others’ work. As Robin Fox and Lionel Tiger (Rutgers) pointed out, this soli- darity among human sociobiologists probably reflects the still largely embattled status of evolutionists within the social sciences. While injudicious insider attacks can shred a new discipline, a ban on internal criticism can only impede scientific development, and hardly improves the chances of any new field being taken seriously.

Examination of human behavioural traits, as of any other aspect of biological diversity, can advance

‘TREE vol. 5, no. I, January 7990

(>ur understanding of evolutionary Drocesses, and should be of interest YO any evolutionary ecologist reading TREE. Did any papers at this con- ,‘erence make such a contribution? ‘This is as yet a tall order, and it is aerhaps unsurprising that my two ‘:andidates are based on mathemat- cal models rather than empirical data, given the problems with inves- ,tigating variation, heritability and fitness in a long-lived species, Dccupying what is probably a highly stypical environment, and on which the potential for experimentation is limited.

Noting that reciprocity is unlikely to 4voIve in large groups as a result of natural selection, Robert Boyd (UC Los Angeles) and Peter Richerson [UC Davis) showed that strategies for cooperation that punish non- cooperators and non-punishers can become stable, even in large groups. Interestingly, similarly policed strat- egies can also cause individually costly behaviour to become evol- utionarily stable, if the costs of punishing are less than the costs of the behaviour in question. This model may help us in tackling a thorny issue - the prevalence of ap- parently maladaptive traits in both human and non-human populations where individuals are able to monitor systematically the interactions of others.

Voluntary limitation of fertility poses another major challenge to evolutionary biologists interested in human affairs. Alan Rogers (Utah) presented a simple model that helps to identify whether a parental strat- egy maximizing either wealth or sur- viving offspring leads to the fastest rate of growth in the number of an individual’s descendants, in cases where parental resources are in- herited by their offspring. Under a range of conditions, higher fitness is achieved through a strategy that maximizes wealth rather than family size. In societies where the conditions of the model are met, Rogers pro- poses that human evolutionary ecol- ogy, properly done, should be economics.

What of future directions? At the final discussion panel, Richard Dawkins (Oxford) issued two warn- ings. The first was against evol- utionary explanations that fail to specify what is actually under selec- tion. Just such confusion underlies the disagreements13 between evol- utionary anthropologists who study specific behavioural traits and evol- utionary psychologists and psy- chiatrists who focus on general motivational or specific logical com- plexes. Until the links between cogni-

tive states, physiological processes and behaviour are better understood the question is unanswerable; we can only generate and test different pre- dictions from our assumptions. At present, representatives of each dis- cipline cling to their traditional focus (be it behaviour or the psyche), while recognizing the potential comp- lementarity of other approaches.

Dawkins’ second warning con- cerned the use of the term ‘evolution’ without any clearly defined selective process. This raises a serious ques- tion14, posed in slightly different ways by Edward Wilson (Harvard), George Williams (Stony Brook) and William Hamilton (Oxford), of whether laterally transmitted cultural traits should be investigated using non-DNA-based models of evolution. Models from epidemiology were the favoured candidates, at least among the discussants. In a strange twist of alliances, several social scientists, coming from disciplines wedded for over 100 years to the concept of ‘cultural evolution’, queried the util- ity of such models: they pointed out that cultural traits (a.k.a. memes or culturgens) are extremely difficult to identify empirically, and that their spread is not entirely independent of the fitness of their hosts. In short, it is by no means resolved whether the future of evolutionary biology as ap-

plied to humans lies in models of biological or cultural evolution, or in an interaction between the two14.

References 1 Wilson, E.O. (1975) Sociobiology, Harvard 2 Borgerhoff Mulder, M. (1988) Trends Ecol. Evol. 3.260-264 3 Daly, M. and Wilson, M. (1984) in infanticide (Hausfater, G. and Hrdy, S.B., eds), pp. 487-502, Aldine 4 McGuire, M.T. and Troisi, A. (1987) Ethel. Sociobiol. 8, 9S-25s 5 Ruse, M. (1986) Taking Darwin Serious/y, Blackwell 6 Irons, W.G. (1979) in Evolutionary Biology and Human Social Behavior (Chagnon, N. and Irons, W., eds), pp. 257-272, Duxbury 7 Tinbergen, N. (1963) Z. Tierpsychol. 20, 410-433 8 Foley, R.A. in Comparative Socioecology (Standen, V. and Foley, R.A., eds), pp. 473-494, Blackwell 9 Caro, T.M. and Borgerhoff Mulder, M. (1987) Ethel. Sociobiol. 8, 61-72 10 Hinde, R.A. (1987) Individuals, Relationships and Culture, Cambridge 11 Betzig, L.L. (1989) &ho/. Sociobiol. 10, 315-324 12 Tooby, J. and Cosmides, L. (1989) Ethel. Sociobiol. 10, 29-49 13 Symons, D. (1989) &ho/. Sociobiol. 10,131-144 14 Boyd, R. and Richerson, P.J. (1985) Culture and the Evolutionary Process, University of Chicago Press