3.3.4 Biological Theories

3.3.4 Biological Theories
With the advent of the science of brain physiology and the theory of evolution, strong biological theories were entertained beginning in the late 19th century, but lack of scientific knowledge of genetics, combined with race or class biases in the scientists led at first to egregious errors in interpretation. Beginning with Darwin's cousin, Francis Galton (1869), racist or classist eugenicists believed that intelligence is not only heritable, but also unchangeable, so they argued that poor and minority children cannot or should not be raised up (see Gould, 1996).

This history of biological theories of cognition should remind us to be very careful about how and what conclusions are drawn from the latest biological or genetic information. It is now believed, for example, that racial differences were added far too late in evolution to have caused biologically based racial differences in intellectual capacity, and well-designed research supports this conclusion (e.g. Dickens & Flynn, 2006). But human cognition has undoubtedly been shaped by evolution, and some cognitive differences among children are heritable, at least in part. The role of evolution in cognitive development is examined in the new subfield of evolutionary developmental psychology, and the study of the inheritance of cognitive abilities is the field of behavioral genetics.
Evolutionary developmental psychologists have proposed a counterintuitive argument: that children's inability to think like adults-for a limited time in development— may actually help, rather than harm, their chances of survival (Bjorklund, 1997; Bjorklund & Green, 1992). They start with the fact that human children are more immature at birth than any other primate. Children are therefore more defenseless, but also more flexibly open to learn than the offspring of even their nearest evolutionary neighbors. Human children must learn a lot, and fast. Preschoolers are egocentric: they tend to reason from only their own perspective. Although not seeing others' viewpoints has some obvious disadvantages, it has advantages, too. It acts as a kind of cognitive
tunnel vision, shutting out all but the most relevant information. Moreover, information relevant to one's own point of view is better remembered—even by adults—than personally irrelevant information, so egocentrism aids memory. Finally, egocentric preschoolers are likely to overestimate their cognitive abilities and are blissfully ignorant of others' performance, and are thus resistant to the negative effects of failure on their sense of ability to control the world.
Evolutionary developmental psychologists note that play, common to juveniles of most mammalian species, also has survival value (Pellegrini & Bjorklund, 2004). Children learn social roles, social interaction, physical coordination, cultural stories, and, through pretend play, symbol use and creativity. (A primate without built-in instincts needs creativity to survive in varied environments.)

Behavioral geneticists are concerned with biologically based individual differences among children in cognitive, emotional, or social behavior. It would be theoretically useful to know to what degree differences in, say, reading or math abilities are inherited. This work is technically complex and requires subtle interpretation. With the exception of a few specific single-gene disorders, scientists do not yet know the specific differences in a person's genotype (DNA sequences) that underlie differences in cognitive performance, and they strongly suspect that many genes are involved in any complex intellectual skill. Instead, they must infer their conclusions from giving intelligence, vocabulary, or standardized achievement tests to large groups of related individuals, and noting the correlated similarities in their scores. Identical twins share, at least at birth, 100% of their DNA, whereas fraternal twins (and other siblings) share about 50%. If identical twins have higher correlations in achievement test scores than fraternal twins or siblings, a degree of heritability is indicated for the tested cognitive skills. For example, a recent British longitudinal study of thousands of twins (Harlaar, Dale, & Plomin, 2007) has suggested that children's reading scores are stable across elementary school, and that a large proportion of that stability can be attributed to shared genes. And, children who are good in reading are statistically likely also to be good in math (Kovas & Plomin, 2007).
The correlations due to shared environment (shared homes, schools or teachers) are considerably lower, but still significant contributors to the scores (Harlaar, et al., 2007). But interestingly, the relative importance of a good environment is greater for poor families than affluent ones. If all of a sample of children is given every advantage offered by a culture, the differences among them in cognitive ability that remain to be measured are likely due to differences in their inheritance. Poor children still will benefit from enrichment in environmental circumstances to help them reach their full innate potential (Turkheimer, Haley, Waldron, D'Onofrio, & Gottesman, 2003). Finally, and most interestingly, behavioral geneticists have wondered about the role of nonshared environment: If all this is true, why are siblings so different (Plomin & Daniels, 1987; Turkheimer & Waldron, 2000)? Even twins from the same family have nonshared experiences, and they may even strive to be different from one another. This shows up in the data, but is hard to measure accurately, because different children will subjectively experience a teacher or parent differently, or demand different things from them for a host of different reasons. This could affect their cognitive development, but scientists are not sure exactly how. For teachers, a summary of this data might be: yes, cognitive abilities are inherited, but this does not mean that enriching an educational environment cannot also make a significant difference for every child. That something is inherited does not mean it is unchangeable.