That gut feeling

If aliens were to swoop in from outer space and squeeze a human down to see what we’re made of, they would come to the conclusion that cell for cell, we’re mostly bacteria. In fact, single-celled organisms—mostly bacteria—outnumber our own cells 10 to one, and most of them make their home in the gut. The gut, in turn, has evolved a stunningly complex neural network capable of leveraging this bacterial ecosystem for the sake of both physical and psychological well-being. ((http://www.apa.org/monitor/2012/09/gut-feeling.aspx))