On Thu, 1 Feb 2001 [EMAIL PROTECTED] wrote:
>
> I am wondering why a more middle-of-the-road view on this
> question is not being studied (or is it, and I am just
> clueless?)
>
> That is, it makes little sense to say, however convincingly,
> that parents have virtually NO influence on how their
> children turn out< snip>
The problem with this otherwise reasonable point of view is that
there is data on the question, and the data argue otherwise. For
example, Bouchard et al (1990) report the correlation on a
personality test (the MMPI) for identical twins reared apart as
0.50, and for identical twins reared together as 0.49. For a test
of religiosity, it's 0.49 for twins apart, and 0.51 for together;
for social attitudes, it's 0.34 for apart, 0.28 for together. In
other words, identical twins resemble each other in personality
and social attitudes to the same extent whether brought up in the
same family or different. Being brought up in the same family
does have virtually NO influence. This is confirmed by data
showing that the correlation on personality traits of two
unrelated children brought up in the same family is 0.07, i.e.
virtually none (Shaffer, 1999, p. 98, cites Loehlin, 1985 for
this).
Plomin (1994) also cites Loehlin (1992) for data showing that the
shared environment effect of extraversion, neuroticism,
agreeableness, conscientiousness, and openness to experience
range from 0.10 to 0.10, while non-shared plus error values range
from 0.43-0.49 on the same characteristics.
These ideas are nicely summarized by Turkenheimer's (2000) Third
Law:
"A substantial portion of the variation in complex human
behavioral traits is not accounted for by the effects of genes or
families". And that leaves only non-shared environment to account
for them, such as Harris's peer influences.
Two qualifiers: the finding that there is virtually no influence
of family environment on personality and social attitudes is
often extented to IQ, but I think this is incorrect. The data do
show that family environment contributes to IQ. For example
Bouchard's (1990) figures show that the correlation for MZ twins
together for IQ is 0.88, which drops to 0.69 for twins apart.
Plomin (1994) gives the shared environment contribution to IQ as
30%, which is more than his estimate for non-shared (10%).
Adoption studies also indicate a moderate correlation between
unrelated siblings reared together for IQ. So if you want to take
credit for making your kids what they are, claim you made them
smarter rather than more sociable.
The other qualifier is that I agree with Harry Avis that the
conclusions from twin studies are limited by the characteristics
of the sample. It's possible that more extreme variation in
upbringing than is represented in the twin studies might
demonstrate a stronger influence of family environment. But until
someone can show that, it remains unproven.
-Stephen
Bouchard, T., et al (1990). Sources of human psychological
differences: the Minnesota study of twins reared apart.
Science, 250, 223-
Shaffer, D. (1999). Developmental Psychology (5th ed.)
Plomin, R. (1994). The Emanuel Miller Memorial Lecture
1993. Genetic research and identification of environmental
influences. Journal of child psychology and psychiatry, 35,
817-834.
Turkenheimer, E. (2000). Three laws of behaviour genetics and
what they mean. Current Directions in Psychological Science, 9,
160--
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Stephen Black, Ph.D. tel: (819) 822-9600 ext 2470
Department of Psychology fax: (819) 822-9661
Bishop's University e-mail: [EMAIL PROTECTED]
Lennoxville, QC
J1M 1Z7
Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy
Check out TIPS listserv for teachers of psychology at:
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