====== Three Laws of Behavior Genetics and What They Mean ======

Eric Turkheimer\\
Three Laws of Behavior Genetics and What They Mean\\
Current Directions in Psychological Science October 2000 vol. 9 no. 5 160-164\\
DOI: [[http://dx.doi.org/10.1111/1467-8721.00084]]\\
{{:papers:turkheimer00_three_laws_behavior_genetics.pdf|(read this paper)}}


<blockquote Abstract>
Behavior genetics has demonstrated
that genetic variance
is an important component of
variation for all behavioral outcomes,
but variation among
families is not. These results
have led some critics of behavior
genetics to conclude that
heritability is so ubiquitous as
to have few consequences for
scientific understanding of development,
while some behavior
genetic partisans have
concluded that family environment
is not an important cause
of developmental outcomes.
Both views are incorrect. Genotype
is in fact a more systematic
source of variability than
environment, but for reasons
that are methodological rather
than substantive. Development
is fundamentally nonlinear,
interactive, and difficult to control
experimentally. Twin studies
offer a useful methodological
shortcut, but do not show
that genes are more fundamental
than environments.
</blockquote>


The author proposes three laws of behavioral genetics which summarize results across a wide range of behaviors:
  - All human behavioral traits are heritable.
  - The effect of being raised in the same family is smaller than the effect of genes.
  - A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families.

These results are widely accepted in the specialty of behavioral genetics, but the implications are unclear and perhaps troubling within the broader context of human self-understanding.  See [[analysis:nature:0main]].

It's my perception that this paper is part of Eric Turkheimer's effort to get behavior genetics unstuck from the politicized nature/nurture morass.  He proposes that these laws are well established, and that we should move on. Unfortunately, this has proved difficult. Outside behavior genetics, these laws are not only questioned, they are frequently dismissed as either:
  *  having been refuted long ago, or as 
  *  being so morally appalling in their implications that they must not be considered.

And when we //go beyond// the three laws, it only gets worse for the theory that differences in ability are primarily caused by potentially controllable factors such as poverty and education. In particular, there is the reliable failure of attempts to pin down the important causes underlying the unexplained part of individual difference.  This is the ''other_stuff'' term in the in the equation:
  behavior = genes + family + other_stuff
  
This cause of individual difference is usually called non-shared environment. In popular writeups, non-shared environment is most often presented as "good teacher/bad teacher", but the many quantitative studies of teacher performance tend to show only small effects.  See [[analysis/social/education/social_structure]].  There is reason to suspect that a lot of the residue may be non-deterministic (random) developmental variation, see [[http://www.wiringthebrain.com/2009/06/nature-nurture-and-noise.html | Nature, Nurture and Noise]]. Are random differences "innate", [[analysis/nature/innateness_difference | whatever that means]]?  At least the dreaded [[analysis/philosophy/determinism_vs_free_will | determinism]] is avoided, (both genetic determinism //and// social determinism).

{{tag>nurture genetic behavior}}