Three part series on genotypes at the Mermaid's Tale.
Another chapter in the critique of twin studies by Jay Joseph. The problem of
reflection for behavior and identity development as regards genetic
inheritance claims is something I have tried to wrap my mind around.
Joseph summarizes this: “The similar physical appearance and level
of attractiveness of MZAs will elicit more similar
behavior-influencing treatment by their social environments.” The
idea being that if we hold a social environment steady, then some
shared trait, like height, may encourage further shared behaviors and
identity structures within those individuals. Across a given culture
then a simpler shared trait will blossom into a more common shared
trait, one that would hold across all niches of that society. And
hence it will be questionable what a twin study would mean as regards
that complex trait. Without understanding the social influence on
that complex trait, it will then seem to make perfect sense that the
complex trait is genetically shared. In some sense, of course, it is
genetically shared, similar to how slavery often had a shared genetic
component.
We
can also see other complex factors. Take two twin babies, given (for
arguments sake) a shared disposition for crying. The behavioral
interaction of others towards those babies may go on to influence
emotions and behaviors within those babies. However, us humans are
complex behavioral machines. Given an emotional distaste of crying
babies by adults, this will not mean that the response to crying
babies has to be uniform. An adult behavioral response is capable of
being tailored in many ways, such as by scientific thought of the day
or by situational structures, such as care-givers that are more or
less readily available. If across a given society we see rather
shared behavioral responses to crying babies as well as care-givers
rather readily on hand, some further emotional or behavioral
characteristic may develop in these babies in response to those adult
interactions. If more complex behavior and emotional structures arise
out of those dynamics, what will then seem like rather correlated
genetically structured responses will actually have a social dynamic
that is embedded into that more complex trait but arising uniformly
from a simple trait within a shared social response. This also throws
the wrench into dizygotic versus monozygotic analysis.
As
I have previously claimed, this is the problem with trying to
pronounce shared genetic structures when we have no clue as to the
mechanisms involved or even of good definitions and categorizations
of the behaviors (e.g. see some of the wrangling over schizophrenia).
My
first major recognition of this came in a popular book by
Sam Wang and Sandra Aamodt called Welcome to Your Child's Brain.
The book was enjoyable and informative on many levels, though I do
have some critiques.