what evolution is

The issue of who’s going to coordinate our 2nd-year evolutionary biology paper came up the other day. (I haven’t done it for the last couple of years as my ‘other’ job – in the Dean’s office – takes up a fair proportion of my time. But at some point I’d like to get back into it.

We’ve had that paper, Evolution and Diversity of Life, on the books for a long time. When I first came here it was more of a diversity course, looking at the different plant & animal taxa, & while the topic of evolution was there it was more implicit than explicit at times. When I took over as coordinator I left things as they were for the first year or so, while I looked at content, curriculum & all that. And then, with several colleagues, I brought in changes that meant that we are now much more explicit in our teaching of evolution. This is because we’d found that many students weren’t really clear on what the word evolution actually means.

So we changed things to help them find out – there’s a lot of research out there showing that simply telling students ‘stuff’ (be that concepts in electronics or ideas in evolution) has hardly any effect on their understanding of the material. Getting them interactively involved, on the other hand, can work wonders. Story-telling’s good, too – with a concept like evolution, simply telling students ‘this is what it is’ isn’t particularly helpful in enhancing their understanding. But using narrative to show the history of how the theory of evolution developed, now that can make a difference.

And for a major concept like evolution, which underpins all of modern biology, it’s really important that students have a good understanding of what it means.

Evolution can be used in three inter-related ways. First up, evolution is a fact. There is now a very large body of evidence supporting the understanding that all living things have evolved through a process that Darwin characterised as ‘descent with modification’ from some common ancestor. Biogeography, palaeontology, embryology, molecular biology; all provide evidence of the fact of evolution.

People can also talk about evolutionary history – the pathways by which organisms arrived in their current state. I’ve written before about the evolutionary pathway of vision (here & here, for example) and of the tiny middle-ear bones in mammals (which are derived from bones in the reptilian jaw articulation). These days a lot of those evolutionary relationships are elucidated using comparisons of DNA sequences (& those of you sitting L3 Biology this year will have seen some of the cladograms, or ‘family trees’, that this work generates), but the fossil record has provided & continues to provide a significant amount of information. For example, both fossil evidence & DNA data support the idea that the most recent common ancestor of humans and chimps lived around 5-7 million years ago.

And of course, there’s the theory of evolution. Theory in the strong scientific sense of a cohesive explanation for a large body of data, which is consistent with those data and which provides testable predictions. The theory of evolution offers a mechanism by which the fact of evolution has occurred and which underlies those evolutionary pathways. (That should read ‘mechanisms’ really: while Darwin’s original mechanism, natural selection, is a key player, genetic drift also has a role to play.)

So there you are: what evolution is. And why we should take care to teach it carefully and well.

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Anyone interested in a bit of extra reading might want to have a look at Evolution: the first four billion years. Haven’t read it myself yet (apart from the intro, which shaped my thinking for this post) but it’s been recommended to me.

M. Ruse & J. Travis (eds.) (2009) Evolution: The First Four Billion Years. Belknap Press