In the tropical forests of Central and South America a struggle for survival has been taking place – not between two mighty giants of the jungle, but between some brightly colored butterflies and a family of climbing plants.

One of the most striking features of ungulates is that many of them – and the ruminants in particular have horns or antlers. Often these are very long or complex structure, and in the case of deer they are shed and regrown each year, a process that uses up a good deal of energy. They are obviously important. If such heavy, apparently cumbersome and energy absorbing structures were of little use, the processes of natural selection would have got rid of them long ago. So what are they for?

What instinct brings them together, and what is it that will guide those summer generations back to a remote mountain enclave as far as 2,000 miles away? So far, those mysteries remain impenetrable.