Stage 3 Stage 4 Stage 5 Stage 6

GENERAL AND SPECIFIC DOMAINS OF MIND IN DEVELOPMENT

Stage 3 Stage 3 Stage 4 Stage 5 Stage 6

3 8 12 18

5-6 6-1 1.5 1 1.5-36 ?

3-4.5 4.5-10 39 39

2.5-6 6-1 1.5 11.5-36 24-48

1-4 2.5-5 none none

9-1 2 12 none none

Note. From Origins of lntelligencet The Evolution of Cognitive Development in Monkeys, Apes, and Hu-

mans (pp. 73-76), by S. T. Parker and M. L. McKinney, 1999, Baltimore: Johns Hopkins University Press.

Copyright 1999 by Johns Hopkins University Press. Adapted with permission.

and apes is not integrated; different abilities develop at different rates.

The pattern shown

by

human children, in contrast, reflects synchronous development and is consistent with Piaget’s explanation that a single sym- bolic function underlies cognitive development.

Necessary cautions must be taken when interpreting these findings, of course. There are limited data for many sensorimotor contents for many species, and sometimes only human-reared apes attain many of Substage

6

accomplishments, which presumably require mental representation (see Call

& Tomasello, 1996). Some researchers have attributed apes’ performance

on these tasks to lower level (nonrepresentational) processes (Heyes,

1998;

Povinelli, Bering, & Giambrone,

2000).

Nonetheless, Parker and McKin-

ney’s compilation and interpretation of the primate findings provide a valu- able database for making inferences about human cognitive evolution.

Parker and McKinney’s interpretation of these findings revolves around the concept of heterochrony, discussed in chapter

4.

Heterochrony refers to differential timing of ontogeny that affects the eventual phenotype of an organism. As discussed briefly in chapter

4,

Parker and McKinney’s claim is that the cognitive developmental data on primates indicate a recapitulation of cognitive evolution, such that hominid phylogenetic changes are best interpreted as reflecting additions to the adult stages of ancestors (terminal extensions; see Langer,

1998, 2000;

McKinney, 1998,

2000; S. T.

Parker, 1996;

S. T.

Parker

6r

McKinney, 1999). The basic argument is that primates traverse the same sequence of sensorimotor stages, with apes attaining higher stages (evolutionarily new stages) than monkeys, and humans attaining yet higher (and newer) stages than gorillas, orangutans, and chimpanzees (those reflected

by

preoperations and beyond). These extensions are afforded by an extended juvenile period (in apes relative to monkeys, and in humans relative to apes), which permits time for brain development to continue beyond the levels attained

by

the ancestors.

We believe that these arguments make sense, and we basically concur with the interpretations of Parker, McKinney, and their colleagues on the evolution of Piagetian-like intelligence. However, we believe that intelli- gence is multifaceted and that a Piagetian-like, domain-general intelligence exists alongside other more domain-specific abilities, which have their own phylogenetic history. Although monkeys, apes, and humans share a common ancestor and primitive cognitive abilities, each group also surely has evolved species-specific cognitive adaptations, suited to their particular ecological niche.

Cognitive primatologists have generally asked how apes and monkeys are like us, using humans as the “standard,” a reasonable approach when the goal is to understand human cognitive evolution. However, apes may have evolved different cognitive abilities that are not very human-like since we last shared a common ancestor with them, as Homo supiens surely have evolved their own set of cognitive specializations. Our point is that human cognition and cognitive development include both domain-general and domain-specific abilities, each of which evolved and is compatible with an evolutionary developmental psychological perspective.

The Co-Evolution of Domain-General and Domain-Specific Abilities Parker and McKinney ( 1999) proposed that ape cognition involves the use of various combinations of skills in different contexts, which requires cognitive flexibility, in contrast to the modular position advocated by

CLASSIFYING COGNITION I43

contemporary evolutionary psychologists. Over the course of evolution, the genetic line that led to Homo supiens simply expanded this flexible intelligence, adding concrete operational abilities in Homo erectus and formal operational abilities in Homo supiens. Mithen (1996) has made a similar claim, proposing that hominids evolved powerful, domain-specific modules to deal with their natural and social worlds,

but

it was not until the emergence of modem humans about

100,000

years ago that Homo supiens were able to integrate the information-processing abilities of these modules to produce a general-purpose intelligence.

In

both cases, it appears that a domain- general mechanism is proposed as the necessary addition for the emergence of the modem human mind.

Under what conditions should domain-general versus domain-specific abilities evolve? Domain-specific mechanisms will be favored when environ- ments remain relatively stable, with individuals facing recurrent problems generation after generation. For Homo supiens, characteristics of social orga- nization, such as male-male competition, female care for and provisioning of young, kin recognition, reciprocal social interactions, and aspects of mate selection, likely remained relatively stable over evolutionary time.

As

a result, we should expect domain-specific mechanisms to have evolved to deal with these classes of problems, and evolutionary psychologists have devoted much time to demonstrating exactly this (Buss,

1995;

Tooby &

Cosmides, 1992). In contrast, domain-general mechanisms will be favored when environments are unstable and the nature of the problems individuals face varies over generations. Under these circumstances, flexible, decontex- tualized problem-solving routines would be most adaptive (MacDonald &

Geary,

2000).

For example, we noted in chapter

2

that the environment in which humans evolved was characterized

by

frequent and noncyclic changes in climate (Potts,

2000). This

would have resulted in unpredictable changes in habitat, requiring individuals to be able to respond to situations unlike any their recent ancestors faced. It is exactly in such situations that flexible, domain-general mechanisms would be favored.

Given the evidence from human cognition and cognitive development indicating the existence of domain-general and domain-specific abilities, data from comparative cognitive development, and evidence of the condi- tions under which our species evolved, both domain-general and domain- specific abilities should be considered as plausible components of the evolved human mind. We believe that such a stance, although perhaps at odds with the canonical interpretations of evolutionary psychology and the develop- mental systems approach, best reflects the extant evidence and can be interpreted within a framework that considers that cognitive abilities evolved in the dynamic interaction between developing organisms and their environments.