Evolution, 4th Edition

596 CHAPTER 22

Human behavior: Evolution and culture

Darwin devoted a book, The Expression of the Emotions in Man and Animals [31], to

the thesis that rudimentary homologues of human mental abilities and emotions

can be seen in other species. Most animals are capable of learning, and we have

seen that some nonhuman primates make tools and have a rudimentary ability

to use language (see Chapter 21). Social interactions, including reciprocal aid and

alliances, are quite elaborate in some primates, leading researchers to describe

“baboon metaphysics” [28] and “chimpanzee politics” [36].

It would be contrary to everything we know about evolution to suppose that

the hominid lineage has diverged so far from other apes that there should remain

no trace of homology in the inherited components of our brain organization and

behavior, or that the human brain should be a completely blank slate, without

genetically determined predispositions. Evolutionary psychologists have com-

piled a long list of supposedly universal, and thus perhaps genetically determined,

human behavioral tendencies and capacities, such as fear of snakes, body adorn-

ment, cooperation, death rituals, division of labor, sex differences in aggression

and dominance, marriage, and the capacity for language [17, 92]. But everyone rec-

ognizes that the expression of most such behaviors is culturally highly variable. All

humans speak a grammatical language, for example, but grammar and vocabulary

vary greatly. In almost all species, many traits express phenotypic plasticity (see

Chapter 6), the capacity of a genotype to express different phenotypes depending

on environmental conditions. Thus, it could be the case that our ancestors evolved

a propensity to respond to certain conditions in specific ways—aggressively or

cooperatively, for example—but that the expressed behavior depends on cultural

and other aspects of the environment.

Several schools of evolutionary research on human behavior have developed in

the last few decades [66]. Human sociobiology, announced by E. O. Wilson in 1975,

proposed to interpret a wide range of behaviors (such as conflicts between off-

spring and parents) as adaptations that had evolved by natural selection, especially

kin selection and reciprocity [119]. This approach has been succeeded by several

other movements. One is human behavioral ecology, which uses adaptive models to

predict and explain a variety of behaviors, including cultural norms. For instance,

we may ask why, in polygynous societies, a woman would choose to marry a man

who already has one or more wives. Adopting a model that was first developed to

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_22.07.ai Date 02-02-2017

Average number of children

Mothers Maternal

aunts

Paternal

aunts

Sons and

daughters

of maternal

grandparents

Sons and

daughters

of paternal

grandparents

Likelihood of sharingX chromosome: 1.0 0.75 0 0.25–1.0 0

1.50

1.75

2.0

2.25

2.50

2.75

1.25

Homosexual men

Heterosexual men

Relatives of:

FIGURE 22.7 Does male homosexuality reflect a

polymorphism maintained by intralocus sexual conflict?

In northern Italy, women who are likely to share an X

chromosome with a male relative have a significantly

higher number of children if the male relative is homo-

sexual than if he is heterosexual. (Data from [24].)

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