On Tue, 27 Apr 1999, Jim Clark wrote:
>
> A colleague in biology is interested in what is known about the
> causes of lower intelligence levels, on average, for twins and
> for other siblings born close together. Any suggestions for
> reading would be appreciated.
I'd suggest checking out Robert Zajonc's confluence theory, which
proposes that a child's intellect depends on the average intellectual
level of all family members. So the more in the family, the lower the
level, and later borns have lower IQs than earlier borns. Spacing is
important in this theory, which would predict lower intelligence
levels for twins.
(Before any later borns or twins (hello Beth) get in a snit over this
I note that while there is some support for the theory, the size of
the predicted effects is very small)
See:
Zajonc, R., & Markus, G. (1975) Birth order and intellectual
development. Psychological Review, 82, 74-88
Zajonc, R. & Mullally, P. (1997). Birth order: reconciling
conflicting effects. American Psychologist, 52, 685-699,
-Stephen
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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
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