If you are a woman and have ever felt that nature has perhaps not been impartial in giving you a fair share of faculties, look no further.
As the work of Dr Valerie J Grant, an evolutionary psychologist at The University of Auckland in New Zealand, has determined, there is strong evidence to suggest that the sex of a newborn is determined in large part by the personality traits and hormonal profile of the mother. In a paper that has given her worldwide renown, Sex determination and the maternal dominance hypothesis, Dr Grant explains how.
The maternal dominance hypothesis
On the basis of the results coming from a series of studies carried out over a 30-year period, various social scientists have identified ‘consistent, statistically significant evidence’ to support the view that there is a “maternal involvement in the predetermination of the sex of her infant.”
What is this maternal involvement?
As incredible as it sounds, the maternal involvement at hand is that women with dominant personality types have consistently been found to be as much as 80% more likely to give birth to sons.
How come?
• Dominance is a personality trait in humans that is characterised by sub-traits such as being “influential, ascendant, prevailing, authoritative or high-in-control.” In their entirety, a dominant person is an individual who can be found “acting overtly so as to change the views or actions of another.”
• As such, dominance in humans is underpinned by the hormone testosterone, with a high correlation between scoring high on dominance personality tests or other markers and serum (blood) testosterone levels.
• The sex of an infant is determined by whether, at the time of conception, the woman’s eggs are fertilised by a sperm bearing an ‘X’ (female) or ‘Y’ (male) chromosome. According to Dr Grant, high testosterone levels at this time in the woman will prime her to be receptive to the latter (Y chromosome) and lead to the development of a male infant.
• In her paper Dr Grant identifies: A meta-analysis of all studies showed that women who later bore sons were significantly more likely to have scored higher on the tests of dominance than those who later bore daughters.
But that’s just the half of it. Dr Grant refreshes the maternal dominance hypothesis with studies showing that personality traits and an individual’s hormonal profile are rooted in a ‘complex two-way interaction between biological as well as environmental influences.’ In other words, any changes in an individual’s status-quo that is tied to dominant behaviour is likely to be accompanied with changes in testosterone levels. Think of a divorced, single-mother previously working to raise several children, now getting married to a wealthy and protective man. According to Grant’s work, with the ceasing of dominant-status their would likely be a decline in its hormonal basis (testosterone.)
As such, small to moderate variations may occur across the lifetime of a woman. For a small percentage of women who are at either end of ‘high dominance’ or ‘low dominance’ these fluctuations may be inconsequential. For the vast majority, however, even very small variations in the amount of testosterone will suffice to “take them either side of a critical threshold.. (leading) to the conception of a male or female infant.”
And that’s good news too, since, as evolutionary biologists are quick to point out, it seems like nature has endowed women with the power to strongly influence the sex of the infant in favour of the one their personalities are most suited to raise. Not bad!
Published in The Express Tribune, January 28th, 2013.
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