444 Part V Biological/Evolutionary Theories
sexual activity, than will thin men or men with less dominant looks (Mazur,
Halpern, & Udry, 1994). These are heritable because the shape of one’s face or
body is mostly controlled by genetics.Nonadaptive Sources
Some sources of individuals do not benefit survival or reproductive success and
hence are categorized as “nonadaptive.” The most common nonadaptive source of
individual differences is neutral genetic variations, which most often take the form
of genetic mutations. Some mutations are neutral in that they are neither harmful
nor beneficial to the individual. They may stay in the gene pool indefinitely until
pressures of natural or sexual selection eliminate them.Maladaptive Sources
Maladaptive traits are those that actively harm one’s chance for survival or
decrease one’s sexual attractiveness. These can stem from either genetic or
environmental sources. One genetic source is genetic defect, but in this case the
mutation is harmful to the person. An environmental source is seen in environmental
trauma, such as brain or spinal cord injury, which can also lead to maladaptive
individual differences.Neo-Bussian Evolutionary Theories of Personality
David Buss was the first to formally propose a complete evolutionary theory of
personality, but others have followed and made advances to the theory. MacDonald
(1995), for example, furthered Buss’s theory with two main contributions. First,
he tied personality more closely to evolved motivational and emotional systems,
and second he argued that the range of personality variation we see on the main
dimensions of personality are viable alternative strategies for maximizing fitness.
MacDonald, similar to Buss, also tied personality dimensions to evolved
strategies for solving adaptive problems. These behavioral strategies are
connected either with motivation to approach or avoid situations or with the
emotional system of negative or positive affect. MacDonald, however, only
had four personality dimensions (dominance, conscientiousness, nurturance,
and neuroticism) and left out openness.
MacDonald further argued that it is adaptive for a species to produce
individuals that vary along a continuum in their responses to important problems
because changing environments require different responses. That is what
MacDonald means by “viable alternative strategies for maximizing fitness.” For
instance, in relatively safe environments, anxiety and vigilance are not as adap-
tive as they are in relatively dangerous environments. Animals can afford to be
bold in safer environments. Some environments may favor risk takers and other
environments may favor risk avoiders. Indeed, in nonhuman animals we see just
such adaptive changes to changing environments (Nettle, 2006). For example,
in Guppie fish populations with relatively few predators, boldness is a common
trait, but if predators are introduced, this trait becomes less common in just a