The journey of life

Our bodies are constantly changing. Can a written account keep up, asks Claire Ainsworth Life Unfolding: How the human  body creates itself by Jamie Davies, Oxford University Press, £20 “ANY one can make things,  if they will take time and trouble enough: but it  is not every one  who, like me,  can make things make themselves.” This scene, pictured right,  from Charles Kingsley’s fairy  tale The Water Babies has stuck  in my mind ever since I read it  as a child. In it, Mother Carey,  the old woman of the sea, turns old beasts into new by simply watching animals create their own bodies from next to nothing. Kingsley, a Victorian clergyman and supporter of Charles Darwin, penned his fairy tale partly to satirise Darwin’s opponents. But  in Mother Carey, he unwittingly touched on another concept,  then unformed, that now vies with evolution to be the most beautiful idea in biology. This concept, adaptive selforganisation, explains how complex things, such as animal bodies, build themselves from simple parts, such as individual cells and molecules. There is  no engineer controlling this construction process. Instead, molecules and cells interact according to simple rules,  creating a whole that is greater than the sum of its parts. Adaptive self-organisation is the theme of Jamie Davies’s Life Unfolding, which tells the story of how the human body

Here’s looking at you, kid: how do we grow up to be complex adults?

develops from the moment of conception. Davies is a professor of experimental anatomy at the University of Edinburgh in the UK. He has spent years studying how organs form in embryos. It’s an ideal perspective from which to describe our journey from fertilised egg to an adult formed of trillions of cells. Davies explains how simple interactions create complex structures: for example, the interface between two different
types of cell will trigger the formation of a third kind of cell at their boundary. An embryo  can construct complex tissues this way, with different cell types in all the right places. A short, final section shows how from these interactions we can deduce “rules” of embryo development. For example, cells communicate with each other and tweak their behaviour in response to changes in their environments. This is what puts the “adaptive” into adaptive self-organisation, ensuring that development can cope with noise or disruption. A nice example of this is the way tiny blood vessels called capillaries manage to cater to different kinds of tissue, even while these tissues are moving and growing. A feedback loop exists between oxygen and a cell protein called HIF-1-alpha. Oxygen normally causes HIF-1-alpha to be destroyed. If a tissue lacks oxygen, HIF-1-alpha levels rise, triggering a cellular signal encouraging capillaries to grow. This brings in oxygen, which shuts down  HIF-1-alpha and halts capillary development. Should the tissue “ Adaptive self-organisation vies with evolution to be the most beautiful idea in biology” then grow, oxygen levels will  fall again, and the loop is set in motion once more. Far from unweaving the rainbow of development, Davies’s lucid and eloquent story increases the reader’s sense of wonder.  The ideas and examples come thick and fast. Anyone without  an A level in biology will find themselves on a steep learning curve. But reading a book that stretches your brain is no bad thing, particularly as the concepts here extend beyond development and even beyond biology. The principles of adaptive selforganisation are already being applied to tissue engineering and technologies like swarm robotics. Mother Carey’s claim to fame may not be hers for much longer.  ■