Evolution has left the human body as a botch job – the evidence is in our feet, backs, and childbirth

Evolution has left the human body as a botch job – the evidence is in our feet, backs, and childbirth

Who hasn’t experienced the exquisite sensation of twisting their ankle playing sport, or hurting their back lifting something awkward, or their baby’s head crowning during childbirth?  OK, I haven’t had the pleasure of the last one, but apparently it’s the price we pay as the most successful primate ever.

At the annual meeting of the American Association for the Advancement of Science (AAAS) in Boston this week, a panel of anthropologists used examples from the fossil record to show how our 7 billion-strong species’ domination of the planet has come at a painful cost to our bodies.  Our ability to walk upright on 2 legs and think abstract thoughts are the result of imperfect tweaks to the body plan of an ancient ape that was adapted to live in trees.

Anthropologist Jeremy DeSilva said: “This anatomy isn’t what you’d design from scratch.”  Using the example of the human foot, he explained: “You wouldn’t design it out of 26 moving parts.”  Our foot has 26 bones in it because our ape-like ancestors needed flexible feet to grab hold of branches.  As we began to move from climbing trees to the walking the ground from around 5 million years ago, our feet had to become a more stable platform for our upright bodies.  Our big toes aligned with our other toes and stopped being opposable; we also developed arches as shock absorbers.  However, all those delicate bones still allow our feet to pivot and twist, and to sprain and break.  And this is not a new problem – even 3 million year old fossils show broken ankles that have healed.  DeSilva said that the epitome of foot design for upright walking and running is that of the ostrich, which has ankle and lower leg bones fused into a single structure, and just two toes to stabilise the foot in running mode.  “Why can’t I have a foot like that?” he asked.  Because ostriches had a 225 million year evolutionary head start on us in walking upright.

Paleoanthropologist Bruce Latimer said: “If you want one place cobbled together with duct tape and paper clips, it’s the back.”  The spine evolved to be stiff and horizontal for moving along the boughs of trees.  When humans stood upright, the spine was vertical and had to support and balance our heavy torso and head – Latimer compared it to stacking 26 cups and saucers on top of each other, then balancing a melon on top.  The result is that the spine has to curve inwards and is shaped like an ‘S’.  This creates pressure and the back problems that are the 6th leading human health complaint in the world.  Latimer cheerfully said: “If you take care of it, your spine will get you through to about 40 or 50.  After that, you’re on your own.”

Paleoanthropologist Karen Rosenberg explained how the growth of our big, complex brains clashed with the limitations of the narrow human birth canal.  Human babies are, on average, 6.1% of their mother’s body size compared with chimpanzee babies (3.3%) and gorilla babies (2.7%).  This is why (I’m reliably told) labour is so incredibly painful.  In fact, it is potentially lethal – childbirth used to be leading cause of death for women in their  reproductive years.  To survive extinction, our female ancestors relied on social support in childbirth.  The term ‘midwife’ is from the Old English ‘midwyf’, literally ‘with-woman’, and midwives are mentioned in the earliest written records.  In the modern developed world, that social support now mostly comes from medically trained midwives and doctors.  Medical intervention has also resulted in the development of painkilling drugs to relieve the pain of childbirth and in procedures like caesarean sections, which now account for around 25% of all UK births and 30% of all births in the US.

Anthropologist Matt Cartmill summed up by saying Evolution doesn’t ‘design’ anything, it deals with changing habitats by doing the best it can with the little it has.  He said:  “Evolution doesn’t act to yield perfection, it acts to yield function.”

Human vs Ostrich - Ostrich foot is 225 million years more refined by evolution for walking and running upright on two legs
Human vs Ostrich – Ostrich foot is 225 million years more refined by evolution for walking and running upright on two legs

Source: ScienceNOW

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Posted by Abroad in the Yard on Friday, 14 August 2015