Dr. Alan Packer, Senior Editor of Nature Genetics, contacted me recently and asked to publicly comment on my recent post on Evolution News and Views entitled Spit-Brain Research. My post was critical of a press release about an article published in Nature Genetics . I am grateful for his observations. My reply follows in my next post.
Michael Egnor has been kind enough to allow me to contribute a comment on his recent post ‘Spit-Brain Research’. The post discussed work by George Perry, Nathaniel Dominy and colleagues, published in a paper entitled “Diet and the evolution of human amylase gene copy number”. As one of the editors at Nature Genetics, where the paper was published, I was pleased to see the paper receive so much attention. I was concerned, however, by what in my view was the highly misleading nature of Dr. Egnor’s post. I would like to make three general points, so that readers of this site will have a fuller picture of what was in the paper, and what was not:
(1) “Spit-Brain Research’ opens with the assertion that evolutionary theory is outlandishly speculative, and in support of this notes that “a paper in Nature Genetics offers a new theory to account for the human brain: spit”. If you click on the word “paper”, however, you will go not to the manuscript by Perry et al. (or the freely accessible abstract), but to a press release put out by the University of California, Santa Cruz, where some of the work was carried out. A more forthright account would have explicitly stated that the entire post is based on a press release, not on the contents of the actual paper, as readers who failed to follow the link could be forgiven if they assumed Egnor was quoting directly from the published work. In fact, the paper by Perry et al. makes no claim whatsoever for a link between “spit” and human brain evolution (the word “brain” never appears in the paper). At the end of his post, Egnor says “Nature [sic] lauds a research paper that asserts that groundbreaking insight into the origin of the human brain can be gained by extrapolating from the comparative biology of spit”. Again, this is incorrect, as the research paper asserted no such thing.
(2) Egnor, in my view, also fails to represent accurately the content of the press release, putting words in Dr. Dominy’s mouth so as to make his comments seem outlandish. Egnor has Dominy “Solving the ‘big mystery’ of paleoanthropology” (human brain evolution). A fair-minded reader will see that Dominy nowhere makes such a broad claim. Rather, Dominy specifically focuses on the possible role of salivary amylase levels as one factor in the evolution of human diet and population growth.
(3) Finally, Egnor says that this research “would have languished on dusty shelves” if the authors hadn’t made claims related to human brain evolution. But the paper has received so much attention not for these nonexistent “claims”, but for the fascinating genetic data that Egnor dismisses. The authors follow up on published evidence that individuals have a different number of copies of the gene encoding salivary amylase by showing that this correlates with the amount of salivary amylase actually produced. The study of inter-individual gene copy number variation is one of the most exciting areas of human genetics, and is likely to explain a significant amount of human variation. Moreover, Perry, Dominy and colleagues report a correlation of salivary amylase gene copy number with the level of starch in the diet of various human populations. This strongly suggests that the human genome has evolved in response to changes in diet (the genetics of lactose intolerance is another recent example of this). This conclusion is supported by robust statistical methods for inferring positive selection in the genome.
Dr. Egnor may not accept any of this, or may think it’s uninteresting, but his misrepresentation of the scientific record suggests he doesn’t trust his readers to make up their own minds.
Alan Packer, Ph.D.