Uprooting the Tree of Life

Yesterday I wrote a post about a cool new transition fossil. When writing it I was more than once tempted to make some kind of reference to the Tree of Life, but I resisted. Why? Put simply: because it would be wrong. There was a time when everyone, even people who were totally on board with evolution by natural selection, was under the impression that the species we see wriggling around today could be traced neatly back, branch by branch, to the ancestor that is common to all life and that those species that looked physically similar did so because they shared a branch on the tree. In the metaphor today's animals are represented by the fresh new shoots and buds on the mighty oak of life; each bud forms a neat ladder ever back to the base of the trunk that started everything, but this picture can lead to many misconceptions about evolution. A more modern understanding of the theory and the evidence we now have paints a different picture. The Tree of Life is dead, say hello to the Shrubbery of Life!

The traditional, misleading view of the Tree of Life

Actually, people generally say the Bush of Life but I saw a chance to use the word shrubbery and I ran with it. Instead of thinking of a perfect, archetypal tree that a 6 year old might draw, think of a tangled mess of thorns full of jagged twigs, thick and choking, jutting this way and that such that you can barely tell where one branch begins and another ends. This is the far better analogy. It allows for the possibility of animals arriving at the same physical niche via a variety of evolutionary paths. It also rules out the idea that as life evolves it moves ever upwards in an increasingly complicated and intricate manner, this isn't the case. Some species 'devolve', or lose features that they had previously evolved; some, like coelacanths or nautili, remain unchanged for millions of years.

Worry not, if you have a poster on your child's bedroom wall like the one on the right I'm not about to tear it down and set fire to it. But the next time you have a chat about it, as you undoubtedly do, use it as an opportunity to highlight that the reality is actually a lot more nuanced and complicated than we often like to think, just like every other single topic worth having a chat about.