In the neuropsychological literature, there is periodic discussion on why left-handed women, women generally, as a group that are less often left-handed than men, birth more left-handed children than left-handed men.

Long story short, the three-discipline, central thesis of this website states that a mother’s uterine testosterone levels determine her children’s testosterone levels and their maturation rates.  The sexes tend to emerge as complementary opposites.  A high-testosterone (T) woman birthing high T girls and low-testosterone (t) boys.  A low t mother births high T boys and low t girls.  A person’s testosterone levels inform that person’s maturation rate.

An individual’s testosterone levels also inform their social structure proclivity.  High T females mate with low t males in our hypothetical matrifocal society.  (We hypothesize estrogen is a vital matching variable, but because we are suggesting that estrogen plays little part in the establishment of maturation rates and proclivity toward left-handedness, I’m leaving estrogen out of this part of this discussion.) When a mother’s uterine testosterone levels radically change, or a high T mother experiences environmental prods further elevating T levels, her progeny can reflect that elevation both in their testosterone levels and in their maturation rates.

What then happens is a shift in time.

I hypothesize that we evolved over hundreds of thousands of years from mostly matrifocal societies into patrifocal societies over the last 50,000 years but particularly in the last 6,500.  As children acquire maturation rate changes through their mother’s testosterone levels that propel them to a matrifocal past, they shift back physiologically, neurologically and hormonally to a former ancestral prototype.

We perform an ontogenetic slide in the opposite direction than we’d been going.  Males with lower t ontogenetically delay instead of accelerating.  Males accelerate in a patrifocal society over time.  Females with higher T ontogenetically accelerate instead of delaying.  Females delay (acquire neotenic features) in a patrifocal society.

A mother’s changing testosterone levels can reverse a son’s or daughter’s ontogenetic and evolutionary direction.

Over the course of our matrifocal evolution, accelerating females acquired language first, practicing left-cerebral dominance first, reflected in a more common use of the right hand.  Acceleration involves the condensation or drawing of features that appeared later in the ontogeny of ancestors (i.e., during adulthood) into earlier ontogeny, transposing features of adulthood into youth.  Right-hemisphere synapse pruning, perhaps an echo of pubertal synapse pruning appearing earlier in ontogeny, resulted in the nonrandom-handed brain with two different sized hemispheres and a smaller corpus callosum at the root of language use and right-handedness.

Women got language and right-handedness first.  These, the high T, maturational accelerated, matrifocal females preceded the low t, maturational delayed, neotenous, patrifocal females popular today.

So, why do left-handed mothers give birth to more left-handed children than left-handed fathers?  Because left-handed mothers are grounded further back in time.  For a woman to be left-handed, she is not only revealing a feature more ancient than all right-handed men but older than all right-handed women that came before all right-handed men.  The emergence of male right-handedness followed female right-handedness, revealing itself only after the shift toward patriarchy.

Of the four prototypes–left-handed women, left-handed men, right-handed women and right-handed men–the left-handed woman is the oldest, most ancient human genotype on the planet.  Her children are more often left-handed because the other three don’t draw so deeply from the past.

Conducting Google searches for interesting word combinations (“balanced polymorphism” annett baron-cohen) I just came across a study, “Sex Differences in Left-Handedness: A Meta-Analysis of 144 Studies” by Marietta Papadatou-Pastou, Maryanne Martin, Marcus R. Munafo and Gregory V. Jones.  There were a number of interesting citations.  One passage jumped out.  In the Scandinavian countries (Sweden, Norway and Finland), there appears the following anomaly, “Overall, the present study provides a powerful test of the hypothesis of a sex difference in handedness.  We have shown using objective statistical procedures that the sex difference is robust for all the commonly used conceptions of left-handedness, with men having significantly greater odds of being left-handed than women (except, it appears, in Scandinavia).”

The study concludes that there are more male than female left-handers in the societies studied.  Not so much in Scandinavia.  This would support our emerging thesis that the Scandinavian countries are revealing a different balanced polymorphism drifting in the direction of a higher percentage of matrifocal social structure predilection individuals (high T females, low t males).  We would also predict higher incidence of left-handedness.


This entry was posted on Sunday, January 25th, 2009 at 9:06 am and is filed under lefthanded, Ontogeny. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
2 Comments so far

  1. asyanis on May 9, 2009 4:56 am

    great findings! very useful to me coz im lefthanded woman hahaa thanxx

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