Does early or late puberty determine neuropsychological profiles ?

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  One of the outstanding biological sex differences is that girls reach puberty before boys do.   The age at which puberty is achieved could,  conceivably,  influence brain organization.  The brain is certainly still developing at puberty.  For example,  it is known that myelinization (envelopment of neurons by fatty insulating sheaths) of the axons of the corpus callosum reaches completion only in adolescence.    So,  supposing girls have greater verbal skills because they reach puberty early,  and supposing boys have greater visuospatial skills because they reach puberty late,  then should we not predict that the same cognitive effects ought to be observed in girls and boys with very precocious or very tardive puberty ?   Several authors have now investigated this theme.   First, when normally distributed cohorts are investigated, one notices that early puberty is mildly related to high cognitive ability as a whole (independently of gender),  and that the high cognitive ability actually antedates the puberty.   So what is being observed in early puberty is probably a trait simply associated with healthy rapid development.    The results are different when more extreme cases of precocious and delayed puberty are compared.   The idea of measuring verbal and visuospatial abilities in very precocious and very delayed puberty was first put to test by a researcher called Deborah Waber in 1976.  She found that delayed puberty was indeed associated with high visuospatial ability,  in both sexes,  just as predicted.   She also found that precocious puberty was associated with high verbal ability,  a finding also in the direction predicted by our simple gender model outlined above.   There have since been at least three attempts to replicate this finding.   Though all three obtained significant results,  they were contradictory from one investigation to the other.   So it is not possible at present to claim that precocious or delayed puberty has a systematic effect on brain organization in any way related to sex differences.  

Further research on this theme certainly does need to be carried out.  Such research is complicated by the fact that very precocious and very delayed puberty is often associated with major endocrinological disorders,  so severe that they can in fact affect cognitive abilities.  Furthermore,   sex differences in cognitive profiles antedate puberty in normal development,  so it would be implausible to believe that pubertal precocity should explain much of the variance in sex differences in cognitive abilities.  And of course,  there could be a causal relation between prenatal sex hormone metabolism and timing of puberty.  In fact, this has been found to be the case in the sheep:  research has shown that in this species prenatal androgens can masculinize patterns of gonadotropin secretion, and the timing of reproductive neuroendocrine maturation after birth is programmed by androgens in utero. There is little reason to think that other mammals should be any different.  Finally,   the puberty-onset model of cognitive profiles predicts that visuospatial abilities should be lower in girls or women who had an early puberty.    Girls reach puberty much younger today in industrialized countries than they did say 50 years ago.  Yet their visuospatial skills have actually improved over this time period.   Both effects are probably partly due to the same cause.  People eat more proteins,  and they also eat more meat that comes from hormonally manipulated animals having received growth hormones to speed up their development to reduce the time from birth to market to reduce production costs.   Both of these changes have accelerated the development of human beings.   In addition,  intelligence keeps going up with every generation ever since IQ tests have existed.   Despite all the chest beating that goes on about how the school system is degenerating in North America, I think it is producing ever greater intellectual development of the general population.   I suspect that in addition to that,  the evolution of schooling, of television and of the other media has also increasingly contributed to improved general intellectual development of children  -despite the common belief to the effect that the mass media are brain killers.   What all of this boils down to is that the puberty-onset model is interesting,  but cannot be plausibly be invoked as a very important factor in sex differences in cognitive ability.