Gifted Issues Discussion homepage Forums General Discussion Birth order and student performance

One of the scientific theories I read regarding why this birth order effect occurs is as follows.

Initially, the female parent has a strong mechanism to reduce the effect of testoterone levels on male neurological development.  Each male pregnancy reduces the strength of this mechanism for future males.

As each males prenatal testosterone level is determined by the individual male's genes, the effect will be seen to occur over a large sample size, but not necessarily within an individual family.

So if the first male has high testosterone levels and the fourth male has low testosterone levels, then you might see the opposite end result than what the study would suggest happens on average.

Realize the studies did not determine if all females have this suspected mechanism.