This is the 2007 version. Click here for the 2017 chapter 08 table of contents.

Evolutionary Psychology

Students of animal behavior have been applying concepts from ethology to human behavior for decades. Tinbergen and Lorenz saw ways in which their concepts applied to humans, and their ideas were popularized by authors like Desmond Morris, who wrote a bestseller in 1967 called The Naked Ape, full of speculations about how various species-typical behaviors of humans might have evolved.

Lorenz's student Iraneous Eibl-Eibesfeldt made human ethology his specialty. He applied the field observational techniques of ethology to humans, recording behavior of people in native cultures with the side-viewing technique described in Chapter 1. Eibl-Eibesfeldt wrote a textbook called Human Ethology (1989) that introduced ethological concepts and showed how they applied to humans.

The 1990s saw the publication of many books and articles using the phrase evolutionary psychology. Like sociobiology and human ethology, this discipline interprets human behavior as a manifestation of underlying neural circuitry modified by evolution. Evolutionary psychologists explain common tendencies of humans by analyzing their adaptive value. Topics studied by evoluitionary psychologists include the following:

1. Factors influencing mate selection

Researchers have found that people generally find statistically average faces more attractive than faces with extreme features. Humans (and animals) prefer symmetry of the body and face in a potential mate. Not surprisingly, people also like healthy skin and consider it more attractive than blemished or diseased skin.

2. Nonverbal and largely automatic forms of social communication

Humans, like other animals, have species-typical displays. Eibl-Eibesfeldt studied the eyebrow flash (briefly raised eyebrows) that serves as a recognition signal and invitation to interaction (but don't do it in Japan, where it is considered crude and sexual). Eibl-Eibesfelt verified an observation made by Margaret Mead, the anthropologist: that young girls of many cultures use a stereotyped flirtation display (a glance, followed by looking away, covering the face, giggling, and looking back). Eckhard Hess showed that pupil size telegraphed the emotional state of a human and altering the pupil size in photographs would change people's evaluation of pictures. Paul Ekman became famous for documenting basic, universally interpretable human facial expressions found in all cultures. By studying the anatomy of facial muscles, he went on to catalogue the full range of possible facial expressions, of which only a subset are frequently used by any culture. David R. Buss and his laboratory in Texas has a long record of studying unconscious social signalling among young dating-age adults, such as the "neck cant" (a sexy tilt of the head, common in females), fiddling with hair (common when a person wants to impress somebody of the opposite sex) and other signals of body language and posture. Many of Buss's observations were made unobtrusively by his research assistants at places like bars and beaches where young single people meet and assess each other.

3. Simulations and models of evolutionary processes

Some psychologists use mathematical or computer models to predict how individuals with particular traits could interact in large populations. The impact of traits on the population as a whole can be modeled on a computer, given certain starting assumptions. Game theory can be used to study social cooperation or competition, negotation or predation.

4. Adaptive function of things we take for granted

What is the adaptive function of a yawn? For primates, it is a dominance display. However, it also cools the brain. Competing explanations sometimes lead to competing predictions that can be tested with research, or it could be (as in this example) that a behavior turns out to have multiple functions.

5. Evolutionary explanations of strange or repugnant events

Honor killings and jealous rages by spurned males may have "worked" in the ancestral environment. Women who stay with an abuser may be acting out an ancient script that was once genetically advantageous. The Stockholm Syndrome (in which kidnapped people bond with their captors) may have been an adaptive response in ancient times. Somnomania (as speculated earlier in Chapter 3, p.132) may have protected males from sneak attacks at night.

Write to Dr. Dewey at

Don't see what you need? Psych Web has over 1,000 pages, so it may be elsewhere on the site. Do a site-specific Google search using the box below.

Custom Search

Copyright © 2007-2011 Russ Dewey