 3
Personality psychology aspires to be the 
broadest, most integrative, branch of the 
psychological sciences. Its content is not re -
stricted to particular subsets of psychological 
phenomena, such as information processing, 
social interaction, or deviations from nor -
mality. Personality psychologists historically 
have attempted to synthesize and integrate 
these diverse phenomena into a larger uni -
fying theory that includes the whole person 
in the myriad modes of functioning (McAd -
ams, 1997; Pervin, 1990). Moreover, per -
sonality theorists have attempted to concep -
tualize the place of whole persons within the 
broader matrix of groups and society. Our 
central argument in this chapter is that these 
theoretical goals cannot be attained without 
an explicit consideration of the causal pro -
cesses that gave rise to the mechanisms of 
mind that define human nature.
Although there has been much debate 
about the definition of personality, two 
major themes have pervaded nearly all efforts 
at grand personality theorizing: human na -
ture and individual differences (Buss, 1984). 
Human nature deals with the common char -
acteristics of humans, the shared motives, 
goals, and psychological mechanisms that 
are either universal or nearly universal. Pro -
posed species-  typical motives range from 
the sexual and aggressive instincts postu -
lated by Freud (1905/1953) to the motives to get along and get ahead postulated by 
Hogan (1983). A proper conceptualization 
of human nature, however, is much larger 
than the forces that impel people out of bed 
in the morning and motivate them in their 
daily quests. Human nature also includes 
the species-  typical ways in which humans 
make decisions (e.g., selection of mates and 
habitats), the ways humans respond to envi -
ronmental stimuli (e.g., fears of snakes and 
heights are more typical than fears of cars or 
electrical outlets), and even the ways people 
influence and manipulate the world around 
them. No other branch of psychology except 
personality psychology aspires to this broad 
conceptualization of human nature. Person -
ality psychology is also the central branch of 
psychology for which individual differences 
play a prominent role. Indeed, one key func -
tion of personality theory is to identify the 
most important ways in which individuals 
differ from among the infinite dimensions of 
possible difference (e.g., see Goldberg, 1981; 
Norman, 1963; Wiggins, 1979).
These two themes—  human nature and 
individual differences—  ideally should not 
occupy separate and isolated branches of the 
field of personality psychology (Buss, 1984). 
Initial “grand theories” of personality, such 
as those advanced by Freud (1905/1953) 
and others, incorporated propositions about 
ways in which human nature and individual CHAPTER 1
The Evolution of  Human Personality
David M. G. Lewis  
David M. Buss