Andrew: I don't think it's that simple. It is true that DZ twins are
dichorionic - two placentas and chorionic sacs. About 1/3 of MZ are
dichorionic, and the rest of the MZs are monochorionic (shared placenta,
chorionic sac, and, therefore, blood). You would think that monochorionic
twins would be treated more similarly in utero, and thus be made more
similiar, but this isn't always the case. MZ twins who share the same
chorion run a greater risk of "crowding each other out", being more
dissimiliar in birth weight that MZ raised in separate chorionic sacs.
A brief article:
Phelps, J.A., Davis, J.O., & Schartz, K.M. (1997) Nature, Nurture and Twin
Strategies. Current Directions in Psychological Science, 6, 117-121.
Another article (I haven't read it):
Sokol, D.K. Moore, C.A., Rose, R.J., Williams, C.J., Reed, T. & Christian,
J.C. (1995) Intra-pair differences in personality and cognitive abilityv
among young monozygotic twinbs distinguished by chorion type. Behavior
Genetics, 25, 457-466.
If your interest is in separating gene and environment effects, there are
some studies (I can find them with modest effort) that correlate children's
abilitys with fathers' in addition to mothers' abilities. Fathers contribute
DNA but not the uterine environment.
Andrew Swihart wrote:
> It is my understanding that MZ twins share a significantly more similar
> prenatal environment than DZ twins. Could someone briefly explain to me
> the mechanisms which render MZ prenatal environments more similar than
> those for DZ, and direct me to a reference source(s) with the details?
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John W. Kulig [EMAIL PROTECTED]
Department of Psychology http://oz.plymouth.edu
Plymouth State College tel: (603) 535-2468
Plymouth NH USA 03264 fax: (603) 535-2412
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"The only rational way of educating is to be an example - if
one can't help it, a warning example." A. Einstein, 1934.
