Design flaws

Our bodies are far from perfect – and evolution is to blame

A diagram of the male internal reproductive organs

Diagram of the human male reproductive organs

  1. Original position of testes
  2. Kidneys
  3. Ureter
  4. Bladder
  5. Vas deferens
  6. Testes
  7. Penis

‘Big Picture: Evolution’ (2014)

Anyone who has endured the pain of childbirth will surely query the concept of a skilled designer. There are other examples suggesting that if the human body has been designed, it has been botched. We seem to have too many teeth for our jaws, for instance – probably because our jaw size has slimmed down during evolution, possibly because of the change from hunter–gatherer to agriculture-based lifestyles.

Another example is the tube linking the mammalian testis to the penis (the vas deferens), which loops up and over the ureter – a bizarre and seemingly pointless detour. The solution to the riddle lies in the early ancestors of mammals, which had testes inside the body. As they descended during evolution, they could have gone behind or in front of the ureter. By chance, they went behind, so the vas deferens has to loop up and over, gradually lengthening as the testes descended.

Speech has been crucial to our success as a species, but the anatomical modifications underpinning it have an evolutionary downside. Modification to the trachea to enable us to produce speech, plus our upright posture, has brought the trachea and oesophagus together and greatly increased the risk that food will enter the former rather than the latter, leading to choking. This arrangement has its roots in the evolutionary history of our pharynx.

Scientists have even pointed out bizarre, inefficient and potentially deadly quirks in the way the genome is organised that seem incompatible with the idea of a skilled designer.


Questions for discussion

  • What other features of human biology do you think have not been ‘designed’ well by evolution?

About this resource

This resource was first published in ‘Evolution’ in January 2007 and reviewed and updated in December 2014.

Genetics and genomics, Ecology and environment, History
Education levels:
16–19, Continuing professional development