In this article we will discuss about the evolutionary ecological approach to human behaviour.
In general, animal behaviour researchers have been even more insistent that the human sciences need an evolutionary and ecological theoretical framework than that they need ethological methods.
How have more specific lower-level theories imported from animal behaviour informed research on human beings? The question is best answered with some specific examples. One such is anthropologist Monique Borgerhoff Mulder’s use of the Orians-Verner-Willson polygyny threshold model, to make sense of marital transactions in an African society in which polygynous marriage is legitimate and customary- as would be expected from the polygyny threshold theory, women and their relatives opt for marriage to men who are already married, rather than available bachelors, when the polygynist’s resources are sufficient to predict a higher reproductive rate.
A different sort of example is provided by psychologist Nicholas Pound’s use of sperm competition theory, to account for the surprising prevalence and popularity of scenes of polyandrous sexual behaviour in pornography designed for male audiences.
Yet another example is provided by psychologist Catherine Salmon’s use of parental investment theory to predict that firstborn and last-born children will be relatively strongly attached to their parents, whereas middleborns (those with both older and younger siblings) will focus more on reciprocity-based relationships with nonrelatives.
In addition to such particular examples, whole fields of research have been launched by applying evolutionary ecological models to the human case. For example, optimal foraging models originating in non-human behavioural ecology have inspired a substantial body of research on human hunter-gatherers, aimed at elucidating why men hunt in situations in which gathering plant foods would provide a higher rate of caloric returns, and why they hunt the particular prey they do.
Similarly, Trivers and Willard’s theory of condition- dependent parental preferences for sons versus daughters has inspired dozens of human studies, using a wide variety of measures and methods.
Most importantly, certain major theories have had very broad general effects on human research, much as they have had on nonhuman research. The most noteworthy cases in point are Hamilton’s inclusive fitness theory and Trivers’s theory that sex differences in parental investment underpin sexual selection and the evolution of other sex differences.
In fact, the researchers’ estimates of genetic relatedness on the basis of genealogical reconstructions predicted men’s alliances better than did mere kinship terminology, which, in the Yanomamö language, does not distinguish brothers from certain more distant kin who are related by a series of patrilineal links.
Taking a different approach to address much the same issue, Daly and Wilson analyzed homicide case data from a variety of societies and showed that collaborating killers are always much more closely related, on average, than are killers and their victims, findings that refuted a prevalent criminological hypothesis that both violent conflict and cooperation arise within particular relationships in proportion to the frequency and intensity of relationship-specific interaction.
Fratricide, for example, constitutes a tiny proportion of homicides, but brothers comprise a much larger proportion of the relationships among co-offenders who act together to kill a third party. Both of these studies illustrate the fact that kinship is associated with a reduction in conflict and an increase in cooperation, in dangerous situations of male rivalry.
Other research programs inspired by Hamilton’s theory have focused on purely cooperative, rather than violent, actions. For example, using behavioural scan sample methods anthropologist Ray Hames demonstrated that the Yek’wana Indians of Venezuela will help close relatives repeatedly even when those who are helped have not had a chance to reciprocate, and thus will allow “labour debts” to accumulate among kin, whereas the same sorts of cooperative labour on behalf of unrelated friends must be reciprocated before further help will be volunteered.
Additional research inspired by Hamilton’s theory has addressed the question of possible kin recognition cues. Using both interview and unobtrusive observational methods, Daly and Wilson and Regalski and Gaulin showed that all interested parties pay more attention to patrilineal than to matrilineal phenotypic resemblances of infants, and that the distribution of remarks about such resemblance is in accordance with the hypothesis that mothers and mothers’ relatives have an interest in promoting the putative fathers’ confidence that they really are the fathers.
Trivers’s theory of sexually selected sex differences has had an even greater impact on human research than Hamilton’s inclusive fitness theory. Trivers proposed that psychological and behavioural sex differences are largely predictable from the degree to which mothers make a greater investment of time and energy in the rearing of each individual offspring than fathers, with the sex that makes the lesser parental investment being more polygamously inclined, more intensely competitive, and less choosy about potential mates.
This line of thinking has inspired researchers to investigate sex differences in human courtship behaviour, mate-choice criteria and selectivity, sexual advertisement, sexual fantasies, intra sexual competition, jealousy, deception, and how women and men disparage rivals, among other things.
In general, the results are strongly supportive of expectations from parental investment theory. For example, men have consistently been found to be more interested in polygamy and in casual sexual opportunity than women, and to be less choosy about acceptable sexual partners.
Both sexes do exercise selectivity, of course, but Trivers’s theory garners support here too, for it turns out that the sexes’ mate-choice criteria are predictably distinct, with men paying greater attention to cues of fertility and reproductive value and women paying greater attention to cues of resource accrual capability.
There is also considerable evidence that intra sexual competition is more intense and dangerous among men than among women and, moreover, that women and men compete with their same-sex rivals in different ways that reflect the above mate-choice criteria, as individuals of each sex strive to enhance their own attractiveness relative to that of rivals.
The sexes also exhibit differences in the qualitative nature of jealousy in ways that make sense in light of the distinct threats to fitness that infidelity poses- men, who differ from women in being vulnerable to cuckoldry, are relatively concerned about specifically sexual infidelity on the part of their mates, whereas women, who suffer negative fitness consequences from the loss of a mate’s help and resources, are relatively concerned about retaining their mates’ emotional commitment.
Nevertheless, several complications threaten this enterprise. Some of the impediments to such research are ethical. Many experiments that would be enlightening obviously cannot be performed on human beings- we cannot place subjects in a genuine mate-choice situation, cannot manipulate the socio sexual experience of a randomly selected subset of our subjects, and so forth.
Moreover, notions of what constitutes ethically acceptable research are in flux, and have generally been moving in the direction of greater stringency. Not so long ago, psychologists routinely conducted experiments in which subjects might feel embarrassed or diminished.
Such research is increasingly forbidden, and those earlier researchers might be astonished to learn that controversy has now been enjoined about such issues as what constitutes truly informed consent, whether recording people’s behaviour without asking their permission to do so constitutes an invasion of privacy even when the behaviour occurs in public, whether giving some sort of academic credit for experimental participation constitutes undue coercion, and whether deception of any sort can be justified.
Ethical concerns are becoming increasingly prominent in other areas as well, including the legitimate uses of archival data such as police and governmental records that contain potentially identifying information, and contested claims of stakeholder standing in archaeological research, especially when aboriginal peoples protest against research activities in places that they believe to have been occupied by their ancestors.
Closely linked to humankind’s unparalleled degree of social learning and cultural diversity is the unique phenomenon of language. Great efforts have been made to train some sort of linguistic performance in other species, and the results sometimes provide impressive evidence of complex cognitive ability.
However, these efforts have also proven beyond doubt that human language, which is acquired without instruction by every normal toddler, entails an unmatched ability to learn and manipulate arbitrary symbols and to communicate an unlimited diversity of messages, both concrete and abstract.
Does the unique role of language in human communication and cognition imply that our sociality and behavioural decision-making are qualitatively different from those of other animals and require a different conceptual arsenal? Yes and no. On one hand, fields like psycholinguistics have appropriately developed their own concepts and theories for dealing with phenomena that are uniquely human, and the same can be said about such broader disciplines as economics, political science, and history.
On the other hand, consideration of the role of natural selection in shaping human nature is contributing to these uniquely human sciences, and will surely contribute more in the future. The fact that people can talk provides an irresistible source of data-we can simply ask our subjects their ages, numbers of children, and so forth, indeed everything from matrilineal kinship links, sexual histories, and the bride prices paid for women of different reproductive values to desires, preferences, attentional priorities, beliefs, and grievances.
But this list should make it apparent that even though having speaking research subjects makes it possible to ask questions that one can scarcely imagine how to address in other animals, it can also be a source of error.
One obvious problem with relying on utterance as a primary data source is that people tell lies. A cautionary tale is that of Margaret Mead, whose distinguished anthropological career was built largely upon her credulous acceptance of Samoan schoolgirls’ tall tales. Mead became famous for doctoral research that allegedly showed that Samoa is a paradise in which sex is unrestricted, and jealousy, rape, and adolescent adjustment problems are unknown. But none of it was true.
Mead never actually learned the Samoan language and she interviewed only schoolgirls, who later acknowledged that they had deceived her for their amusement. Such gullibility may be especially problematic for researchers operating in exotic settings, but it would be foolish to assume that sharing a culture with one’s interviewees is a guarantee against being duped.
More subtle than simple mendacity is the fact that even an honestly reported memory may be untrue, and memory’s failings are not random but systematically biased. Moreover, even cooperative interviewees have introspective access to only a fraction of the workings of their minds, indeed a smaller part than either they or the scientist questioning them may imagine-a good deal of clever psychological research has shown that people often attribute their behavioural choices to variables that are demonstrably irrelevant, while vehemently denying the relevance of factors that can be shown experimentally to be the real determinants of their choices.
One example is Chagnon’s demonstration that the Yanomamö “manipulate kinship” by stressing those particular genealogical links that bring their acquaintances into useful (e.g., marriage-eligible) categories while ignoring others.
A third example is provided by Salmon’s experimental demonstration that the metaphorical use of kinship terminology, such as calling an unrelated acquaintance “brother,” has persuasive impact on firstborns and lastborns, who also exhibit other signs of a strongly familial social orientation, but has no such impact on middleborns, whose strongest social ties tend to be reciprocal relationships with nonrelatives.
In these and other studies, what people say has been treated as social behaviour in its own right, perhaps representing sincerely informative cooperative acts in some cases and more deceptive acts of disinformation, persuasion, and impression management in others.
The conceptual framework of these studies is therefore much like the contemporary adaptationist approach to nonhuman communication, notwithstanding the much richer information content of human utterances.
Reliance on verbal data begins to get researchers into trouble when they treat the subjects’ recollections as if they were unproblematic records of past behaviour. In areas such as the study of sexual behaviour, we can often do little more than collect self-reports, but we should always be suspicious about their validity.
Survey data regularly indicate, for example, that the average man has had heterosexual relations with more partners than the average woman, but as long as the sexes are about equally numerous this obviously cannot be true, and it is not easy to determine whether men are exaggerating upward, women are exaggerating downward, or both.
The mistake of assuming that recall data provide unbiased record of actual behaviour is surprisingly prevalent in some areas of the social sciences, but fortunately not in the work of evolutionists, who may derive some protection against such gullibility from their long-standing interests in deceptive self-presentation and self-deception.
Nevertheless, evolution-minded students of human behaviour have not been entirely immune to the siren song of abundant verbal data. For example, in an ambitious and widely cited multinational study, Buss asked questionnaire respondents in 37 different societies to rank the importance of a given list of mate-choice criteria, and found that several aspects of the data were cross-culturally consistent- the sexes were consistently alike in ranking a pleasant nature and intelligence highly, and consistently differed in that men ranked physical attractiveness more highly than women did, whereas women ranked resource accrual capabilities more highly than men.
These results are both interesting and readily interpretable, but we should not assume that they provide direct testimony about actual mate- choice criteria, for although people may sincerely believe that they place great weight on certain factors, such as pleasant personality traits, they do not necessarily know what factors really influence their judgments.
So what should researchers do about these problems with self-report data? The answer is clearly not to avoid collecting verbal information from research subjects altogether. Verbal data, including retrospective behavioural data, are too valuable to justify such a drastic remedy.
In human research, even observational studies that rely primarily on behavioural scan samples almost always make use of supplementary verbal data, and any study that tests for effects of age or education or birth order or marital status will generally depend on hearsay rather than observation for at least some of its measures. A researcher’s confidence in data of this sort can be often enhanced by cross-checking with multiple informants.