Is the ASPM gene truly related to brain size?

I had just finished reading the chapter on Phylogeny for the Evolution class, and took a break to clear my head, what with all the terms I’d just gone over – homoplasy, synopomorphy, symplesiomorphy and worse. My break didn’t really turn out to be a break; I ended up reading about a study on the evolution of brain sizes where scientists had traced a particular gene across taxa, and I found I could apply those freshly ingested terms to understand what this study was all about.

Now, again, I first read an article about the study in question, and then briefly went over the original publication. The scientists hypothesised that the ASPM gene, one of many that affect brain size, had evolved rapidly in species as distantly-related as humans, dolphins and whales, to give the large brains that are characteristic of these species. Without going into the details, they indeed concluded that convergent evolution might have acted on the gene in both cetaceans and primates to result in the similarly large brain size.

This fascinating result was falsified recently for what seem to be legitimate reasons. The original work was, it turned out, not statistically significant, but more importantly, it was not very thorough. Unfortunately, they did not study the evolution of the gene in species with smaller brain sizes, and latest research suggests that the ASPM gene need not be specific to large brains, but could be a general target of selection and could have evolved adaptively in all mammals. There are a couple of more details that the original study failed to look at, and the first article linked above summarises them nicely.

The recent publication is more of a short note clarifying certain aspects of the original study without harshly picking on it (too bad; it would have been a nice online fight to follow). Instead, they aim to be constructive and discuss methodological difficulties in this particular field of comparative adaptive genetics (that I am very unfamiliar with). They caution readers about how sensitive it can be to perform explicit hypothesis testing that should be followed by appropriate statistical tests, which seem slightly more complex in this field (details in their paper). They even provide some possible alternatives to overcome some of these problems.

This was a reminder for me, about how making mistakes and talking about them are as important as other results in the growth and development of science. These situations occur in almost all fields, and sometimes the only way to improve ideas, methods, etc., is to be informed of the error(s), even if it means being cited for the wrong reasons!

P.S. It would be great if students/faculty who are familiar with some of this literature could add to this.


About Divya

Predator-prey behaviour fascinates me enough to cross oceans. I wish I could read like Vicki the 'Small Wonder'. When I take a break from all the paper-reading, I read other things, mostly but not necessarily to do with science. I also wish I could write as much as I read, but clearly there needs to be an equilibrium whose stability I cannot guarantee. Also, I usually need the help of music to get me through all the reading and writing. See a pattern?
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