Chapter 36

Individual Differences in Cognition

R. Kim Guenther

People differ with respect to their intellectual capabilities. Historically, the at-
tempt to measure differences in intellectual ability has been the most conspicu-
ous and influential branch of cognitive psychology.

Perspectives on Individual Differences in Intelligence: Hereditarian, Unitary Models
versus Multifaceted, Domain-Specific Models of Intelligence
The assumptions historically made by researchers in the intelligence testing
movement constitute a theory of intelligence that Steven Jay Gould calls the
hereditarian theory(Gould, 1981; also Mackintosh, 1986). The hereditarian theory
of intelligence makes two separate claims. First, it claims that intelligence is
unitary—it is a reflection of an all-purpose system or process that permeates all
intellectual activity. Another way of making this claim is to say that intelligence
isgeneric. An implication of the generic notion is that intelligence is measurable
using tests that are meaningfully converted into numbers that reflect the amount
of intelligence a person possesses. The second claim, from which the hereditarian
theory derives its name, is that the primary basis of intellectual differences
among people is to be found in the genes they inherit; that is, intelligence is
primarilygenetically determined. Although these claims are logically distinct
(intelligence could be unitary but differences among people could still be due
primarily to environmental differences), historically they have been associated.
The main theme of this chapter will be a comparison between the unitary or
generic view of individual cognitive differences, on the one hand, and adomain-
specificormultifacetedview of individual cognitive differences, on the other
(Gardner, 1983). The multifaceted view claims that people may display supe-
rior talent or skill in one intellectual domain without necessarily being superior
in other domains. As I did in chapter 8: Problem Solving, I will champion here
the domain-specific approach to individual intellectual differences. I will also
discuss the evidence for a genetic basis for intellectual differences and try to
make clear what are and are not reasonable implications of this evidence.
Included in the section on the genetic basis of intelligence is a discussion of sex
differences in cognitive skills.

36.1 Historical Background and the Rise of the Heredtarian Theory of Intelligence

A confluence of several developments taking place in the 1800s led to an inter-
est in the measurement of individual differences in cognition, culminating in

From chapter 9 inHuman Cognition(New York: Prentice-Hall, 1998), 313–346. Reprinted with per-
mission.