THE DEVELOPMENTAL SYSTEMS APPROACH

If

evolved psychological mechanisms underlie contemporary behaviors and thought patterns, what role can culture, or experience in general, play?

A common misperception about evolutionary explication is that if an ability is said to have “evolved” or to have an innate component, the result is one of biological, or genetic, determinism. In other words, if it is in the genes (which it seemingly must be if it evolved), it cannot be changed. This is not the case, and evolutionary psychologists are explicit in the role that the environment plays (and played in our evolutionary past) in the expression of evolved psychological mechanisms. However, despite the insistence that explanations based on evolutionary theory are not ones of genetic determin- ism, few evolutionary psychologists have proposed a detailed model of’ how evolved mechanisms interact with the environment to produce behavior.

Providing such a model is one significant contribution of evolutionary devel- opmental psychology.

As

noted above, evolutionary psychologists assume that organisms adapt and evolve, through natural selection, through their transactions with the environment. Organisms affect their environment

(by

choosing and then

“furnishing their niches”), and environments, in turn, affect the organism

(by

changing behaviors to meet the particular demands of a setting). Because of this transactive relation between organism and environment, we must study organisms interacting with their environments if we want to under- stand adaptation and development. This position rejects any simplistic bio- logical determinism such as the theory that genetic endowment has a main effect on cognitive functioning (see Pellegrini & Horvat, 1995, for a discus- sion) or on social development (Pellegrini & Smith, 1998). More specifically, we believe that the developmental systems approach provides a proper appreciation of how biology and environment, at a variety of levels, interact to produce behavior and development, and that such a model can be used to explain how evolved psychological mechanisms are translated into behavior (Gottlieb, 1991a; Kuo, 1967; Lickliter & Berry, 1990; Oyama, 2000a).

The core concept of the developmental systems approach is that of epigenesis, which developmental psychologist Gilbert Gottlieb (

199

1 a) de- fined as “the emergence of new structures and functions during the course of development” (p.

7).

Gottlieb (1991a,

1996, 1998, 2000;

Gottlieb, Wahl- sten, & Lickliter, 1998) stated that epigenesis reflects a bidirectional relation- ship among all levels of biological and experiential factors, such that genetic activity both influences and is influenced by structural maturation, which is bidirectionally related to function and activity. This relationship can be expressed as

genetic activity

(DNA

H

RNA

H proteins)

H structural maturation H function, activity.

According to Gottlieb (1991b),

Individual development is characterized by an increase of complexity of organization (i.e., the emergence of new structural and functional properties and competencies) at all levels of analysis (molecular, subcel- lular, cellular, organismic) as a consequence of horizontal and vertical coactions among the organism’s parts, including organism-environment coactions. (p. 7)

From this perspective, functioning at one level influences functioning at adjacent levels. For example, genes code for the production of protein molecules, which in turn determine the formation of structures such as muscle or nerve cells. But activity of these and surrounding cells can turn on or off a particular gene, causing the commencement or cessation of genetic activity. Also, self-produced activity or stimulation from external sources can

A NEW SCIENCE OF THE DEVELOPING MIND 33

alter the development of sets of cells. From this viewpoint, there are no simple genetic or experiential causes of behavior; all development is the product of epigenesis, with complex interactions occurring among multiple levels. This bidirectional approach to development is expressed in Figure

2.2.

This point was made clear by developmental neuropsychologist Mark Johnson (

1998)

in his review of the neural basis of cognitive development:

Since it has become evident that genes interact with their environment at all levels, including the molecular, there is no aspect of development that can be said to be strictly “genetic,” that is, exclusively a product of information contained in the genes. (p.

4)

Evolved psychological mechanisms can be thought of as genetically coded “messages” that, following epigenetic rules, interact with the environ- ment to produce behavior. Areas of the newborn brain are biased to process certain types of information more effectively than others (e.g., language).

Such information-processing biases derive from genetically specified features of neurons as well as endogenous factors associated with neurons’ own functioning and growth (Changeux,

1985;

Edelman, 1987). With species- typical experience, these sets of neurons become increasingly specialized, enhancing the efficiency of these brain areas for processing specific informa- tion, while decreasing their ability to process other information

(M. H.

Johnson,

2000).

The experiences of each individual are unique, beginning before birth, and if the relations expressed in Figure

2.2

closely mirror reality, there should be substantial plasticity in development. This probabilistic and unpredictable nature of development is captured

by

Oyama’s (2000a) statement that “Fate is constructed, amended, and reconstructed, partly by the emerging organism itself.

It

is known to no one, not even the genes” (p.

137).

This perspective

Bidirectional Influences Environment

(Physical, Social, Cultural) Behavior Neural Activity

Genetic Activity

-

Individual Development

-

Figure 2.2. A simplified schematic of the developmental systems approach, showing a hierarchy of four mutually interacting components.

Note. From Individual development and evolution: The genesis of novel behavior by G. Gottlieb, Oxford University Press, p. 186. Copyright 1992.

seems to be at odds with evolutionary psychology’s contention for universal,

“innate” features (as in the claims of neonativists such as Pinker,

1997).

In fact, despite the fact that genes will be expressed differently in different environments, almost all members of a species (human or otherwise) develop in a species-typical pattern. How can this be so, and the developmental systems perspective, as presented in Figure

2.2,

still be valid?

The answer lies in the fact that humans (or chimpanzees or ducks) inherit not only a species-typical genome but also a species-typical environ- ment. According to Robert Lickliter

(1996),

The organism-environment relationship is one that is structured on both sides. That is, it is a relation between a structured organism and a structured environment. The organism inherits not only its genetic complement, but also the structured organization of the environment into which it is born. (pp. 90-91)

To

the extent that an organism grows up under conditions similar to that in which its species evolved, development will follow a species-typical pattern.

Tooby and Cosmides (

1992)

have argued that complex, psychological mech- anisms evolve only when the environments are relatively stable over many generations. Thus, over long periods of time, members of a species could

“expect” certain types of environments and evolved species-typical solutions to deal with such stable environments.

If

one takes seriously this perspective of development, it requires a modi- fication in the canonical definition of “evolution” presented earlier in this chapter. According to conventional wisdom, evolution is defined as changes in gene frequencies over generations.

It

is genes that evolve, and anyone who disputes this position must have had his or her head in the sand over the past half century. However, organisms also inherit environments, both internal and external, and it is within these environments that genes are expressed and phenotypes derived. From this perspective, what evolve are developmental systems, which include genes but also the varied and interacting environments in which genes exist. According to Oyama (2000b),

What is transmitted between generations is not traits, or blueprints, or symbolic representations of traits, but developmental means (or re-

sources, or interactants). These means include genes, the cellular machin-

ery necessary for their functioning, and the larger developmental con- text, which may include a maternal reproductive system, parental care, or other interaction with conspecifics, as well as relations with other aspects of the animate and inanimate worlds. This context, which is actually a system of partially nested contexts, changes with time, partly as a result of the developmental processes themselves. (p. 29)

Evidence for the influence of species-typical environments on species- typical and presumably “innate” behavior comes from research with precocial

A NEW SCIENCE OF THE DEVELOPING MIND 35

birds. For example, in the wild, a mother duck will lay several eggs in a nest and stay close

by

until they hatch. While in the egg, the ducklings begin to vocalize, and so hear themselves, the vocalizations of their brood mates, and those of their mother. How might these “experiences” influence later species-typical behavior?

The answer is “substantially.” In a procedure developed

by

Gottlieb (1976,

1991b,

1996), ducklings, while still in the egg, were isolated from other eggs and their mother so that they could not hear the vocalizations of other animals. Their vocal chords were also treated so that they could not produce any sound (a condition that wears off several days after hatching).

Following hatching, these animals were placed in a large container and heard the maternal call of two species-their own and another-played through speakers on opposite sides of the container. Most untreated birds in this situation

will

approach the call of their own species, seeming to know “instinctively” which call is that of their species and which is not.

However, ducklings who were prevented from hearing any duck vocaliza- tions-their mothers, those of other ducklings still in their eggs, or their own-failed to make this discrimination and were just as likely to approach the call of an alien species as that of their own. Thus, prehatching experience, particularly the duckling hearing its own vocalizations, plays a critical role in posthatching species-typical behavior. The reason that nearly all ducks approach the species-typical call after hatching is that nearly all ducks inherit not only the genetic disposition to make such a selection but also the species-typical environment that provides the necessary experiences for such a pattern to develop.

Results such as these demonstrate that behaviors (here related to infant-mother attachment) that are found in almost all normal members of a species are influenced

by

often-subtle characteristics of the environment.

Evolved psychological mechanisms at the human level can be viewed simi- larly. Strong specieswide biases may exist for certain behaviors, but how any particular evolved mechanism is expressed will vary with environmental conditions experienced at certain times in development.

How early experience can reorganize the way the brain responds to certain stimuli is illustrated

by

a study of the effects of painful stimulation in neonatal rats (Ruda, Ling, Hohmann, Bo Peng, & Tachibana,

2000).

Neurons in the spinal cord of rats develop during embryonic and early postna- tal times, typically in the absence of noxious stimuli. When newborn rats were caused to experience pain, however, the nerve circuits that respond to pain were permanently rewired, altering their response to sensory stimulation and making the animals more sensitive to pain as adults. Only within the past 20 years have physicians bothered to give young human infants anesthesia for some medical procedures, believing that their perception of painful stimuli

was minimal. These findings suggest that such unexpected stimulation, even if it is not immediately perceived as keenly as by an older individual, can adversely alter the species-typical course of development. Central to the per- spective of evolutionary developmental psychology is the realization that the environment and the organism interact in different ways at different periods of ontogeny. A n implication of this position is that different features may be selected at different points ofdevelopment

(W. D.

Hamilton,

1966).

We now examine aspects of evolutionary psychology that are particularly pertinent to development.

EVOLUTIONARY PSYCHOLOGY AND DEVELOPMENT