In January 2009, Ian Sample, a science correspondent writing for the Guardian opened an article writing,
Charles Darwin’s “tree of life”, which shows how species are related through evolutionary history, is wrong and needs to be replaced, according to leading scientists.
The great naturalist first sketched how species might evolve along branches of an imaginary tree in 1837, an idea that quickly came to symbolise the theory of evolution by natural selection.
In response to claims like these New Zealand evolutionary biologist, Professor David Penny, has written an article in PLoS Biology tackling ’a strong urban myth that Charles Darwin introduced and/or advocated a ’Tree of Life’ for the classification of living organisms.’
Penny’s key points are clearly made:
- Darwin did not coin the phrase ‘the tree of life’, which has much older roots (e.g. within religious texts)
- ’instead of using the tree of life concept, Darwin referred to his theory as ’descent with modification’.’
- In the one instance that Darwin does refer to the ’Tree of Life’ in the Origin of Species it ’is not used as a description of relationships, but rather as an analogy for competition between species (and groups of species) during evolution.’
- Darwin’s words ’asserted the continuity of populations, subspecies, species, sibling species, genera, etc.’, suggesting the importance of this is may be overlooked today
While aimed primarily at biologists, it should be quite readable to non-biologists and I encourage readers to give it go. I would particularly encourage journalists or writers who have occasion to mention Darwin’s work.
In particular, Penny backs his third point citing the passage containing Darwin’s only reference to ‘the tree of life’ in the Origin of Species:
buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications
Penny presents how Darwin was interested in how species might arise–descent with modification–rather than proposing a pattern that might describe how different living forms are related–a tree, network, etc.
With these he points out that it is wrong to refer to it as ’Darwin’s tree of life’ as Ian Sample did.
His article touches on other aspects that I will leave my readers to find for themselves such as Mendelian genetics and the neutral theory of evolution.
He argues for a need for an accurate understanding of what historical works state, suggesting that this would lie in better communication between present-day since and the work of science historians.
In an aside Prof Penny notes that ’several research groups have long advocated an increase in the use of networks in phylogenetics’ – i.e. that viewing life using a network model, rather than a tree, is a not a new concept. Maybe being a New Zealander has biased me (!), but I’ve long felt that that ‘insisting’ analyses use a tree-based framework can be unhelpful, and that for a few applications even networks have limitations.
Other articles on Code for life: