How People Make Their Own Environment: A Theory Of Genotype-Environmental Effects

I. Describe the three kinds of genotype-environmental effects Scarr and McCartney assume and give an example of each.

In a Passive genotype-environmental effect, the genetically related parents provide a rearing environment that is correlated with the genotype (genetic makeup of an organism) of the child. A child's environment is correlated with their genes, which correlate with their parents' genes because he or she is making decisions likely from their own preferences. Passive genotype-environmental effects cannot interpret the direction of effects in parents-child interaction, but also cannot interpret the cause of those effects in biologically related families. An example of a passive genotype-environment can be found negatively in sports. Parents who are skilled track runners faced with a child who is not learning to do sports let alone run track, may provide a more enriched environment for the less able child than for another who acquires track skills quickly. Infant children cannot do as much niche building and seeking out as older children, therefore passive genotype-environment effects are less important to older children who can extend their experiences beyond the family's influences. Older children can create their own environments to a much greater extent. The effects of passive genotype-environment effects wane, or diminish gradually, when the child has many extra familial opportunities.

An Evocative genotype-environmental effect represents different responses that different genotypes evoke from social and physical environments. It is quite likely that smiley, active babies receive more social stimulation than sober, passive infants. For example, cooperative, attentive preschoolers receive more pleasant and instructional interactions from the teachers or adults around them than uncooperative, distractible children.

Active genotype-environment effect, "niche-building sort", is arguably the most powerful connection between people and their environments and the most direct expression of the genotype in experience. Children through active genotype-environment have selection effects that correlate with motivational, personality, and intellectual aspects of their genotypes. Examples of active genotype-environment effects can be found in the selective efforts of individuals in relationships-in life. Once experiences occur, they naturally lead to further experiences. An active genotype-environmental increases over development from infancy to adolescence.

II. What will be the effect of extreme environmental deprivation on these three effects?

Passive genotype-environmental effects from extreme environmental deprivation can hinder a child's intellectual and social development. Extreme environmental deprivation may alter a child's developmental levels from those that would be predicted by the family's phenotype and genotype. The parent-child interaction and the selection of children into school curricula would be affected. It is impossible to ignore the attention and learning characteristics the child brings to the situation so the effects of environmental manipulations are never entirely free of individual differences in genotypes. High intelligence and adoptive skills in children from very disadvantaged backgrounds, for example, evoke approval and support from school personnel who might otherwise despair of the child's chances in life.

In an active genotype-environmental effect, a child's motivation, interest, intelligence or physical stimuli in playing a game of chess (for example) were uprooted, through deprivation his or her self-worth would typically lower that particular activity. Extreme deprivation would diminish a child's impetus experience, or incentive in chess but gain active genotype-environmental effects, in another game that evokes approval.

III. Explain why the correlation between dizygotic twins is greater in infancy and less in school age and older twins whereas it remains the same for monozygotic twins.

In the case of dizygotic, or fraternal twins, a prenatal environment was shared and early childhood years were spent treated similarly by the same biological parents. The correlation is less for school age and older twins because dizygotic twins are no more genetically related than sibs. As the intense similarities of their early environment gives way to different evocative effects and their own choices, they select environments that are less similar