Testing for an Evolved Basis

Every behavioral action occurs because of a combination of interacting genetic and environmental factors. Despite general acceptance of this notion, it is useful to learn whether or not a particular behavior or sex difference has a specific evolved basis. All human behaviors are genetically based because all involve a genetically programmed brain, but only some behaviors are mediated by brain structures that evolved for a specific behavioral purpose. Other behaviors are incidental byproducts of our species' domain-general capacities for perception, learning, cognition, and movement. For example, all chickens will peck at grain, but only some will learn to peck at a disk for food.

Some of the methodologies used in distinguishing between these alternatives will now be outlined. They can provide evidence for or against the presence of an evolved basis for a given anatomical or behavioral trait or sex difference. For further critical discussion of these research strategies, which were pioneered by Darwin (1872/1965) himself, see C. R. Ember (1981), Miller (2002), and G. E. Weisfeld (1982).

Universality. The main research strategy is to distinguish species-wide traits from those that vary across populations. Species-wide anatomical and behavioral traits have an evolved basis, as a rule. Variable traits usually have a cultural basis and are adaptive or neutral for that population but lack a population-specific genetic basis. Like all statements about human behavior, these have exceptions. If the behavior remains the same across this cultural variability, then the behavior probably has an evolved basis. If the behavior or sex difference varies with culture, then genes do not effectively constrain it and it is primarily culturally based.

Developmental Research Strategies. Similar reasoning applies to other research strategies for drawing this distinction between traits with an evolved basis and those that are purely acquired. Another strategy is to minimize the role of culture or socialization in order to see if the behavior still develops. For example, if newborns exhibit the trait, then postnatal socialization can hardly be responsible. If, on the other hand, the behavior or sex difference is absent at birth, then its later appearance is probably due to socialization—although it may be a delayed effect of genes, such as the changes of puberty (C. R. Ember, 1981).

A variant of this secondly strategy in analyzing a sex difference is to hold socialization constant by concealing the gender of infants and noting whether they are still treated the same. If not, then an evolved basis for any sex differences in the infants' behavior is likely. Yet another variant is to identify the onset of some cognitive capacity and see if the sex difference in question appears before this hypothesized cognitive cause. If, for example, children exhibit a particular sex difference before they understand gender differences, then the behavior cannot depend on this comprehension.

Comparative and Physiological Strategies.

A third main strategy is to determine whether or not a human behavior or sex difference also occurs in our primate relatives. If so, then the trait probably was passed on to our species by our forebears and is not rooted in human culture. Similarly, demonstrating a specific neural or hormonal mechanism for a behavior or sex difference renders improbable a purely cultural basis. Many hormonal and brain structural differences between men and women have been correlated with sex differences in behavior (Hampson, 2002).

Interpretation of Data from these Research Strategies. These research strategies are not infallible. For example, a trait that we do not share with even our closest primate relatives, such as speech, may still have an evolved basis because every species possesses some unique traits. A sex difference that occurs in hundreds of cultures except one doubtless has an evolved basis, because culture can always override an evolved behavioral propensity.

Because of these complications, evidence from various strategies is sought in analyzing a given behavior or sex difference. The evidence from various strategies for a given behavior is usually consistent, thereby validating them. For example, cross-cultural, hormonal, and comparative evidence converges to indicate that sex differences in human aggression have an evolved basis (Hoyenga & Hoyenga, 1993).

Also, demonstrating an evolved basis for a behavior does not mean that socialization factors are not also involved. Most behaviors are probably shaped by both types of factor, by information obtained by our ancestors and embodied in our genes, and by information acquired by ourselves through learning and observation.

Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

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