 1. The Evolution of Human Personality 17
this prediction, such as the higher rates of 
child abandonment by men compared with 
women, this hypothesis remains to be tested 
rigorously in studies of parental feeling and 
behavior. The incidence of physical abuse of 
children, to take another example, is rough -
ly 40 times higher in stepfamilies compared 
with genetically intact families, support -
ing the prediction that genetic relatedness 
affects feelings of parental love (Daly & 
Wilson, 1988). Moreover, the evolutionary 
theory of parent–  offspring conflict suggests 
that children will generally desire a higher 
level of parental investment than parents are 
willing to give, since parents are motivated 
to distribute their investments across off -
spring (Trivers, 1974).
Parental motivation, as a core feature of 
human nature, appears to be absent from 
most or all personality theories, although 
Freud clearly signaled the importance of 
relationships with parents in the develop -
ment of personality. Evolutionary psychol -
ogy provides a heuristic for the inclusion of 
this neglected component of human nature 
(see Atherton & Schofield, Chapter 16, this 
volume).
Other Motivational Candidates for  Human  Nature
Status striving, mating motivation, jealousy, 
emotions, and parental motivation are mere -
ly a few of the most obvious candidates for 
a comprehensive theory of human nature. 
Others include the desire to form friend -
ships or dyadic reciprocal alliances (Bleske 
& Buss, 2001), the desire to help and invest 
in kin (Burnstein, Crandall, & Kitayama, 
1994), and the motivation to form and 
join larger coalitions (Tooby & Cosmides, 
1988). An evolutionary perspective leads us 
to anticipate the evolution of many complex 
psychological mechanisms underlying each 
of these forms of social relationships. One 
clear implication is that evolutionary psy -
chology provides a nonarbitrary theoreti -
cal foundation for postulating fundamental 
human motivations, such as “sex and ag -
gression” or “love and power” or “getting 
along and getting ahead.” At the same time, 
it suggests that the postulation of only one 
or a few such motivational tendencies will 
grossly underestimate the complexity of 
human nature.The Evolution of Individual Differences
According to this analysis, individual differ -
ences cannot be divorced from, or consid -
ered apart from, the foundations of human 
nature. Personality theories of individual 
differences, according to this reasoning, 
must have as a foundation a specification of 
human nature. We describe in this section an 
evolutionary framework of individual differ -
ences (see Buss & Greiling, 1999; Keller & 
Miller, 2006; MacDonald, 1995, 1998; Net -
tle, 2006; Penke, Denissen, & Miller, 2007).
This framework includes individual dif -
ferences that emerge from both heritable and 
nonheritable sources. Evidence from behav -
ioral genetic studies of personality strongly 
suggests that both are important. Personal -
ity characteristics commonly show evidence 
of moderate heritability, typically rang -
ing from 30 to 50% (Bouchard & McGue, 
1990; Loehlin, Horn, & Willerman, 1990; 
Plomin, DeFries, & McClearn, 1990). All 
heritable individual differences, of course, 
ultimately originate from mutations—  a 
point we take up later. Simultaneously, these 
studies provide the strongest evidence of 
environmental sources of variance, ranging 
from 50 to 70%. A conceptual taxonomy of 
sources of individual differences based on 
environmental and heritable sources is pre -
sented in Table 1.1.
Differential Input into  Universal  Mechanisms
An understanding of species-  typical psycho -
logical mechanisms can be used as a power -
TABLE 1.1.  Sources of Individual Differences 
in Personality
Environmental sources of individual differences
1. Early experiential calibration
2. Enduring situational evocation
3. Strategic specialization
4. Adaptive self-assessment of strengths and 
weaknesses
Heritable sources of individual differences
1. Balancing selection 1: Temporal or spatial 
variation in selection pressures
2. Balancing selection 2: Negative frequency-
dependent selection
3. Mutation–selection balance 