Why Charles Darwin was wrong about the tree of life.

A sketch from Darwin’s notebook in 1837, showing the tree of life (Photograph: getty images).

In 1837 Charles Darwin scribbled ‘I think’ followed by a thin messy tree (above) which turned out to become one of the most iconic and influential sketches in evolutionary biology. The tree of life is key to his theory of evolution and proposes that genes are simply passed down individual ‘branches’ without any overlap. When a new species is arises they are completely separate from any other.

Dr Chris Jiggins and co from the University of Cambridge examined two exotic and brightly coloured Amazonian butterfly species to explain that the difference between species is not as clear cut as Darwin’s work implies.

Bright black white and red Butterflies

After running around the Amazon frantically swinging nets, they caught two kinds of black butterfly with vibrant splashes of red and white (pictured right). Despite being different species and on separate branches of the tree of life, at any place they looked almost identical, implying that they share genes. It turns out that the two species copy each others bright colours and patterns in order to warn predators that they are poisonous. Any butterfly that didn’t have the same colours and patterns were more likely to be attacked by predators as they were not seen as toxic.

Further insight into the genetics reflects the similarity of these species. Remarkably, there are just four genes that control almost all colour and pattern in both kinds of butterfly, exposing that different species do in fact share genes and there is an overlap of the branches in the tree of life.

The findings revealed that two species of butterfly that are supposedly completely different, shared important genes in predator avoidance, meaning that Darwin’s drawing is far too simple. Instead, evolution is more like a thick web than a simple tree. However, it seems that Darwin himself might have realised this, describing evolution as more of a ‘tangled bank.’