Tag Archives: human evolution

Is the average size of the human head increasing?

I don’t know of any such study. But, I can think of two reasons for the increase in C-sections that aren’t related to increasing head size.

  1. Women with small pelvises died as a consequence of the first birth so never gave birth again. With the advent of safe C-sections they now can go on to have more children.
  2. Since C-sections have become safer doctors are more willing to do a C-section when a labor goes long.

Speaking of evolution though, Neanderthals had larger heads than moderns do. It is also probable that their pregnancies lasted up to 10 months so the infant was better able to survive the cold. So head size is probably not an indicator of much.

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Patrilocal/patriarchical societies

Patrilocal/patriarchical societies are consequence of agriculture not a true reflection human past says Psychology Today in a guest post by Eric Michael Johnson.

The article reports that based on the DNA:

    …the male vs. female “effective population size,” or the percentage of males compared to females who were effectively reproducing. If polygyny were indeed the norm it would mean that most men throughout human evolution never reproduced and, in strictly genetic terms, had mysteriously vanished without a trace.

The article uses evidence of bonobos (pygmy chimps – closest to us genetically) that females mate with many males during estrous.

They postulate that like bonobos early humans – and indeed humans up until the invention of agriculture lived in a multimale-multifemale mating system – both males and females having multiple partners. The discussion is on why this would be so.

My comment:

    There is great sense in multiple mating for females, especially in a highly mobile group, since there is always the possibility that any male might be the father of any offspring then 1) the offspring becomes the concern of all members of the troop 2) females can call on all males with whom she has mated for assistance 3) to keep frustration in a troop at

    a minimum and build group cohesion and 4) if it is a group with decided male dominance in the group, (generally not true of modern hunter/gatherers) then when male dominance changes the chances are that a female already has a relationship with the newly dominant male

    We know that amongst baboons (not as genetically close to us as bonobos) newly dominant males will kill the offspring of the previously dominant male to 1) get rid of possible contenders early 2) to stop the female from nursing and thus bring her in to estrous.

    The issue of paternity doesn't become as important until the invention of scarcity that proceeded the invention of agriculture. Hunter/gatherers tend to see the world as plentiful rather than scarce so everyone shares with everyone else. Once there is scarcity then those who are bigger can take things away from those who are smaller – males can take things, including sex and children away from women. Then it becomes important for a male to know that he is the father of his children.

    Naturally this probably evolved over the couple of thousand years between the beginning of sedentary villages and the full adoption of agriculture.