Teach the controversy

Evolutionary biology is a vibrant field of science, and full of active dispute and uncertainty and new discovery. Science education ideally gives students the basic background so that can find their way around popular descriptions of what is going on at the bleeding edge of research.

Here are some of the controversies that could easily be part of a lesson even in high schools.

1. The Cambrian Explosion. About 530 million years ago, and over a period of some 10 million years or so, there was a dramatic diversification of animal life, the like of which has never been seen before or since. There are a host of unanswered questions and hypotheses about what is involved. When it occurred, how long it lasted, what are the antecedents, what changes took place, what mechanisms were involved. It is seen as an artefact of sampling, giving limited insight to a much more spread out period of change, or as a comparatively abrupt phase shift in the biosphere. It's seen as driven by evolution of exoskeletons, or of vision, or of predation, or of HOX genes. It is seen as driven by oxygenation, or warmer temperature, or changes in the sea floor. On going investigations continue to shed light on this fascinating period, but it's still wide open for new research and ideas.

2. Horizontal transfer verses variation through descent. For the most part, we carry within our bodies the genetic heritage of our ancestors; but there are also possibilities for genetic information to become incorporated into the genome from other organisms or a virus. This is particularly common in bacteria, but it can also occur for more complex organisms. The extent and importance of this is an open research question.

3. Particulars of lineage and relationships. There are many cases in which scientists are uncertain as to the relationships of different organisms. A classic example is the whole dinosaurs to birds issues, though this one is now all but resolved. There are plenty more that remain wide open. One example would be relationships between insectivores (insect eaters -- shrews, hedgehogs, moles, tenrecs, etc). There are many other examples.

4. Drift verses positive selection. It's a common misconception to think of evolution as a kind of continuous progress in improved fitness. Recent decades have given strong support for a notion of neutral drift, and the development of characteristics that are not adaptive, but simply a consequence of accumulated neutral change. What features of an organism actually are adaptive, or a result of positive selection? There are ways to measure this when we have access to a DNA sequence. With fossils and paleospecies it gets more difficult.

5. Target of selection. People often think they understand selection; but what is selected? Is it genes? Individuals? Populations? Species? All of these have been proposed as targets for selection, and the debate continues as to their relative importance.

6. Evolution and behaviour. We are more than our physical forms; we also have tendencies and predilections for different kinds of behaviour. To what extent is behaviour subject to evolution? This is a very difficult and contentious dispute!

7. Physical details of microevolution. There's still a lot we don't know about how development works, and how variation accumulates from generation to generation. What kinds of change can arise in the genome? Genes are far more than a coded protein sequence. They come with promoter regions and splicing points, and ways of encoding multiple proteins depending on how exons are combined. Evolution can duplicate whole genes, or combine them, or alter the regulatory promoters. Some parts of the genome are much more subject to variation than others. What kinds of variation are possible? What is their relativity frequency and importance? What proportion of variation is deleterious? How important is the piggyback effect where selection for one variation carries along other consequences? I'm only touching on the huge range of active research questions here.

I'm not a biologist. If you can educate me further in any of these or add some more, please leave me a comment!

(Disclaimer: this post is a repeat with minor revisions of something I wrote sometime ago in a discussion forum.)

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Update: I omitted to say why I wrote this. It was originally given in the context of creationist notions about teaching the controversy. I intended to contrast what genuine scientific controversy looks like, as opposed to the screwy notions of creationists.