Nature Versus Nurture - Philosophical Difficulties

Philosophical Difficulties

Philosophical questions regarding nature and nurture include the question of the nature of the trait itself, questions of determinism, and whether the question is well posed.

As well as asking if a trait such as IQ is heritable, one can ask what it is about "intelligence" that is being inherited. Similarly, if in a broad set of environments genes account for almost all observed variation in a trait then this raises the notion of genetic determinism and or biological determinism, and the level of analysis which is appropriate for the trait. Finally, as early as 1951, Calvin Hall suggested that discussion opposing nature and nurture was fruitless. Environments may be able to be varied in ways that affect development: This would alter the heritability of the character changes, too. Conversely, if the genetic composition of a population changes, then heritability may also change.

The example of phenylketonuria (PKU) is informative. Untreated, this is a completely penetrant genetic disorder causing brain damage and progressive mental retardation. PKU can be treated by the elimination of phenylalanine from the diet. Hence, a character (PKU) that used to have a virtually perfect heritability is not heritable any more if modern medicine is available (the actual allele causing PKU would still be inherited, but the phenotype PKU would not be expressed anymore). It is useful then to think of what is inherited as a mechanism for breaking down phenylalanine. Separately from this we can consider whether the organism has other mechanisms (for instance a drug that breakdown this amino acid) or does not need the mechanism (due to dietary exclusion).

Similarly, within, say, an inbred strain of mice, no genetic variation is present and every character will have a zero heritability. If the complications of gene–environment interactions and correlations (see above) are added, then it appears to many that heritability, the epitome of the nature–nurture opposition, is "a station passed."

A related concept is the view that the idea that either nature or nurture explains a creature's behavior is an example of the single cause fallacy.