Hidden Disadvantage to Caesarean Section

Some modern health care may end up changing the genetics of the human race. For example, the CLAHRC WM Director established a genetic basis for male infertility,[1] and sure enough, children born following injection of sperm into the mother’s egg have an increased risk of infertility.[2] What about Caesarean section? Childbirth is a struggle because, compared to all other animals (primates included), the baby’s head is big relative to the size of the mother’s pelvis. Evolution allows this to continue under an equilibrium where the distribution of pelvic sizes is maintained at a level where the beneficial effects of big brain/head balances the risk of catastrophic birth from a pelvis below the threshold where risk rises rapidly. Caesarean section skews natural selection and pelvic sizes according to this elegant mathematical model.[3] But are pelvic sizes indeed becoming smaller?

— Richard Lilford, CLAHRC WM Director

References:

  1. Lilford R, Jones AM, Bishop DT, Thornton J, Mueller R. Case-control study of whether subfertility in men is familial. BMJ. 1994; 309: 570.
  2. Belva F, Bonduelle M, Roelants M, et al. Semen quality of young adult ICSI offspring: the first results. Hum Reprod. 2016; 31(12): 2811-20.
  3. Mitteroecker P, Huttegger SM, Fischer B, Pavlicev M. Cliff-edge model of obstetric selection in humans. P Natl Acad Sci USA. 2016.
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One thought on “Hidden Disadvantage to Caesarean Section”

  1. Caesarean Section and Evolution

    We are always evolving – so that Caesarean section will be included in our evolutionary processes. If bigger heads are better(?) heads then there will be a selection advantage to the bigger-headed who will have bigger headed babies. As long as Caesarean section continues, that evolutionary pressure to have bigger headed babies will also continue.

    If Caesarean section became too dangerous – in a post apocalyptic world say – that particular evolutionary pressure would cease.

    We are constantly subjected to evolutionary selection pressure – we just are not conscious of the (very slow) pace or it – nor of the scale!
    Aileen

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