438 Part V Biological/Evolutionary Theories
The process of evolution by natural selection has produced solutions to these
two basic problems of life and they are called mechanisms. More specifically,
mechanisms
∙ operate according to principles in different adaptive domains
∙ number in the dozens or hundreds (maybe even thousands)
∙ are complex solutions to specific adaptive problems (survival, reproduction)
Each mechanism works specifically on the problem it solves and not other ones.
For example, sweat glands solve the problem of regulating body temperature but
do nothing for disease or wounds. Psychological mechanisms operate by converting
input into particular actions or decision rules that help solve these adaptive prob-
lems (D. Buss, 1991).
There are two specific main classes of mechanism, namely physical and
psychological. Physical mechanisms are physiological organs and systems that
evolved to solve problems of survival, whereas psychological mechanisms are
internal and specific cognitive, motivational, and personality systems that solve
specific survival and reproduction problems.
Anatomical and physiological mechanisms are often shared by many species,
whereas psychological mechanisms are often more specific to species. Evolution-
ary biology focuses on the origin of physical mechanisms, whereas evolutionary
psychology focuses on the origin of psychological mechanisms. Indeed, a major
contribution of evolutionary psychology to evolutionary theory is the introduction
and development of psychological mechanisms.
Examples of survival and reproduction problems and their various physical
and psychological solutions are presented in Table 15.1 (Buss, 1991). For exam-
ple, animals of different species have evolved similar sensory systems. In most
vertebrates, and mammals in particular, these take the form of eyes, ears, nose,
skin, and tongue. Senses are adaptive in that they function to take in different
kinds of information from the outside world and allow the organism to respond
appropriately. Sensory mechanisms differ between species of animals. Dogs for
instance, hear sounds with pitches between 10 and 35,000 cycles per second
(Hertz), whereas humans only hear sounds in the 20 to 20,000 cycles per second
(Hertz) range. Humans, however, evolved photoreceptor cells (cones) in the
retina that are sensitive to three different wavelengths of light, namely red, green,
and blue (Jacobs & Nathans, 2009). Dogs, like most other mammals, evolved
cones sensitive to only two wavelengths, namely blue and green (Neitz, Geist,
& Jacobs, 1989). Humans, in other words, have better color vision than dogs,
but dogs hear (and smell) much better than humans. Another physical mechanism
is the immune system, which evolved in response to the problem of parasites
and disease, just as blood clotting developed to solve the problem of dying from
wounds or injury.
An example of a reproductive problem is same-sex competition, which stems
from the fact individuals must compete with members of the same sex for access
to reproduce with the opposite sex. The problem, therefore, is same-sex competition,
or in Buss’s words: “besting members of one’s own sex to gain access to desirable
members of the opposite sex” (1991, p. 465). One solution, but by no means the
only solution, to reproduction is dominance. Individuals who successfully compete