580 vI. SELF‑ AND S OCIAL P ROCESSES
In particular, research and theory on the self 
supports the following conclusions: (1) All 
humans have a sense of self, an “I” and a 
“Me,” but there is considerable individual 
variability in both self-  awareness (the “I”) 
and self-  representations (the “me”); (2) hu -
mans have self-  representations that exist at 
multiple levels (personal, relational, social, 
and collective), and these self-  representations 
are evaluative in nature, contributing to our 
overall feelings of self-worth, or self-  esteem; 
(3) humans start developing a sense of self 
around the age of 18 months, but the self 
does not reach full complexity until much 
later, following a timetable dictated, at least 
in part, by maturation of the underlying cog -
nitive capacities that support the develop -
ment of self-  awareness and self-  conceptions; 
(4) other animals also have a sense of self, 
but one that lacks the complexity of the 
human self; (5) neuroimaging studies and 
studies of patients with neurological dam -
age have identified specific brain regions 
and neural circuitry associated with differ -
ent self-  related processes; and (g) the two 
core features of the self—self-  awareness and 
self- representations—  seem to be evolved as -
pects of human nature that facilitated sur -
vival and reproduction in a complex social 
environment. Just as Darwin (1859) com -
mented on the beauty and variation found 
in the natural world, one might similarly re -
flect on the richness and complexity of the 
human self, which is arguably the feature of 
humanity that makes us most distinct from 
other animals.
I hope that this review of the literature 
has demonstrated that our understanding 
of many personality processes would be im -
poverished without the concept of self. Per -
sonality psychology is an unusually broad 
field, because it covers a wide spectrum 
of phenomena and levels of analysis, from 
genetic markers of traits to neural mecha -
nisms underlying emotions, to lexical stud -
ies of trait adjectives, to motives in personal 
life stories, to sociocultural perspectives on 
identity development. What provides coher -
ence in these diverse themes is an emphasis 
on understanding consistencies in people’s 
thoughts, feelings, and behaviors, and the 
mechanisms that underlie these consisten -
cies. From my perspective, it is the self that 
ties together these various personality pro -cesses and, as Allport (1960) aptly put it, 
“makes the system cohere in any one per -
son” (p. 308).
The psychology of the self has an impor -
tant role to play in the integration of evo -
lutionary biology and neuroscience into 
personality psychology. The self sits in a 
privileged position, encompassing and in -
tegrating all levels of the person from the 
biological to the social. This privileged posi -
tion is fundamentally inclusionary: There is 
ample room, and indeed serious need, for a 
variety of approaches to understanding the 
structure and function of the self and its re -
lation to other basic psychological processes.
An evolutionary perspective on the self 
was central to many early theories of per -
sonality and social behavior, and it must be 
considered a central issue for contemporary 
personality theories. The naturalist agenda 
outlined by James (1890) remains a worth -
while path for research on the science of the 
self. By naturalizing the self, we can move 
the field of personality toward a truly bio -
psychosocial perspective.
NOTES
1. Although James argued for a naturalist view 
early in his career, he later adopted a more spiritual 
stance toward the self, proposing in his 1909 book, 
Pluralistic Universe,  that consciousness may not be 
amenable to scientific explanation.
2. The keyword “self” is clearly overinclusive 
and will detect articles examining psychological 
phenomena beyond the scope of research on the self. 
However, any other keyword (e.g., “self-  esteem,” 
“self-  concept,” “self-  awareness”) is necessarily un -
derinclusive and would fail to detect important as -
pects of the self literature.
3. A related perspective, promoted by cognitive 
scientists and philosophers working in the field of 
“extended cognition,” rejects the notion of a sealed 
off unitary self and instead views conscious aware -
ness as an extension of, and interdependent with, the 
external world (e.g., Clark, 2008; Menary, 2010).
4. How the brain generates self-  representations 
is considered a much simpler problem, since this is 
assumed to be the same process through which the 
brain generates any kind of semantic knowledge, 
such as knowledge about other people and things.
5. Narcissistic behavior also seems to be pres -
ent and in some cases adaptive in nonhuman ani -
mals. Sapolsky (1997) described an orangutan 
named Hobbes the “cocky son of a high-  ranking 