How People Make Their Own Environments

How People Make Their Own Environments: A Theory of Genotype --> Environment Effects
Sandra Scarr and Kathleen McCartney (1983)
Yale University

Abstract

We propose a theory of development in which experience is directed by genotypes. Genotypic differences are proposed to affect phenotypic differences, both directly and through experience, via 3 kinds of genotype --> environment effects: a passive kind, through environments provided by biologically related parents; an evocative kind, through responses elicited by individuals from others; and an active kind, through the selection of different environments by different people. The theory adapts the 3 kinds of genotype-environment correlations proposed by Plomin, DeFries, and Loehlin in a developmental model that is used to explain results from studies of deprivation, intervention, twins, and families.

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Short personal summary:

Genotypes not only influence traits directly but also determine which environments people encounter, how they respond to them, and which experiences they actively seek.

The theory distinguishes between three types of genotype–environment correlation:

• Passive: parents provide both genes and gene-correlated environments.

• Evocative: individuals evoke responses from others based on genetically influenced traits.

• Active: individuals select or build niches that match their dispositions (the strongest influence over time).

As children grow, passive effects decline, while active effects increase, making personal choice a stronger channel of genetic influence. This explains why identical twins—even reared apart—are so similar, while adopted siblings grow less alike.

In short: genes drive experience by guiding exposure to, selection of, and responses from environments.

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"In this paper we propose a theory of environmental effects on human development that emphasizes the role of the genotype in determining not only which environments are experienced by individuals but also which environments individuals seek for themselves."

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"Genetic variation must be associated with phenotypic variation, or there could be no evolution."

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"We argue that genetic differences prompt differences in which environments are experienced and what effects they may have. In this view, the genotype, in both its species specificity and its individual variability, largely determines environmental effects on development, because the genotype determines the organism's responsiveness to environmental opportunities."

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"Because there is no evidence that new adaptations can arise out of the environment without maturational changes in the organism, genotypes must be the source of new structures."

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"As Gottlieb (1976) said, there is evidence for a role of environment in (1) maintaining existing structures and in (2) elaborating existing structures; however, there is no evidence that the environment has a role in (3) inducing new structures. In development, new adaptations or structures cannot arise out of experience per se."

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"The dichotomy of nature and nurture has always been a bad one, not only for the oft-cited reasons that both are required for development, but because a false parallel arises between the two. We propose that development is indeed the result of nature and nurture but that genes drive experience."

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"A good theory of the environment can only be one in which experience is guided by genotypes that both push and restrain experiences."

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"Like Chomsky and Fodor (1980), we propose that the genotype is the driving force behind development, because, we argue, it is the discriminator of what environments are actually experienced. The genotype determines the responsiveness of the person to those environmental opportunities."

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"we stress the role of the genotype in determining which environments are actually experienced and what effects they have on the developing person."

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"We distinguish here between environments to which a person is exposed and environments that are actively experienced or "grasped" by the person. As we all know, the relevance of environments changes with development. The toddler who has "caught on" to the idea that things have names and who demands the names for everything is experiencing a fundamentally different verbal environment from what she experienced before, even though her parents talked to her extensively in infancy. The young adolescent who played baseball with the boy next door and now finds herself hopelessly in love with him is experiencing her friend's companionship in a new way."

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"Because the child's genotype influences both the phenotype and the rearing environment, their correlation is a function of the genotype."

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"developmental changes in the genetic program ... prompt new experiences"

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"the child becomes attentive to the language environment receptively months before real words are produced."

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"some genotypes are more likely to receive and select certain environments than others."

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"a passive kind, whereby the genetically related parents provide a rearing environment that is correlated with the genotype of the child"

"an evocative kind, whereby the child receives responses from others that are influenced by his genotype;"

"an active kind that represents the child's selective attention to and learning from aspects of his environment that are influenced by his genotype and indirectly correlated with those of his biological relatives."

"The relative importance of the three kinds of genotype --> environment effects changes with development. The influence of the passive kind declines from infancy to adolescence, and the importance of the active kind increases over the same period. "

"The degree to which experience is influenced by individual genotypes increases with development and with the shift from passive to active genotype -- environment effects, as individuals select their own experiences." 

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"Because parents provide both genes and environments for their biological offspring, the child's environment is necessarily correlated with her genes, because her genes are correlated with her parents' genes, and the parents' genes are correlated with the rearing environment they provide."

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"genotype -> environment effect is called evocative because it represents the different responses that different genotypes evoke from the social and physical environments"

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"The third kind of genotype --> environment effect is the active, niche-picking or niche-building sort. People seek out environments they find compatible and stimulating. We all select from the surrounding environment some aspects to which to respond, learn about, or ignore. Our selections are correlated with motivational, personality, and intellectual aspects of our genotypes. The active genotype - environment effect, we argue, is the most powerful connection between people and their environments and the most direct expression of the genotype in experience."

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"Examples of active genotype -> environment effects can be found in the selective efforts of individuals in sports, scholarship, relationships-in life. Once experiences occur, they naturally lead to further experiences. We agree that phenotypes are elaborated and maintained by environments, but the impetus for the experience comes, we argue, from the genotype."

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"Although infants are active in structuring their experiences by selectively attending to what is offered, they cannot do as much seeking out and nichebuilding as older children;"

"the effects of passive genotype -> environment effects wane when the child has many extrafamilial opportunities."

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"Genotype -> environment effects of the evocative sort persist throughout life, as we elicit responses from others based on many personal, genotype related characteristics from appearance to personality and intellect."

"Similarities in personal characteristics evoke similar responses from others, as shown in the case of identical twins reared apart"

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"We argue like McCall that nature has not left essential human development at the mercy of experiences that may or may not be encountered;"

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"Phenotypic variation among individuals relies on experiential differences that are determined by genetic differences rather than on differences among environmental effects that occur randomly. "

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"most often genotypes and environments are correlated in the real world"

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"monozygotic (MZ) twins come to be more similar than dizygotic (DZ) twins, and biological siblings more similar than adopted siblings on all measurable characteristics, at least by the end of adolescence"

"the declining similarities between DZ twins and adopted siblings from infancy to adolescence."

"unexpected similarities between identical twins reared in different homes"

"A theory of genotype-environment correlation can account for these findings by pointing to the degree of genetic resemblance and the degree of similarity in the environments that would be experienced by the co-twins and sibs."

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"One would certainly predict what is often observed: that the hobbies, food preferences, choices of friends, academic achievements, and so forth of the MZ twins are very similar (Scarr & Carter-Saltzman, 1980)."

"We propose that the home environments provided by the parents, the responses that the co-twins evoke from others, and the active choices they make in their environments lead to striking similarities through genotypically determined correlations in their learning histories. "

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"the selective placement estimates from studies by Scarr and Weinberg (1977) can account for most of the resemblance between adoptive parents and their children."

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"The theory put forward here predicts that the relative importance of passive versus active genotype-environment correlations changes with age."

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"The social psychology literature on attractiveness (Bersheid & Walster, 1974; Mursteid, 1972), for example, would seem to support our view that some personal characteristics evoke differential responses from others. Similarly, teachers' responses to children with high versus low intelligence, hyperactivity versus acceptable levels of energy, and so forth provide some evidence for our theory."

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"Our theory predicts that children select and build niches that are correlated with their talents, interests, and personality characteristics"

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"With a rich array of opportunities, however, most differences among people arise from genetically determined differences in the experiences to which they are attracted and which they evoke from their environments. "