Methylomes

DNA methylation is the term for a modification to certain DNA bases that involves the addition of a methyl group. This slows down gene expression, which may or may not be advantageous in context – though if you remove it entirely in mice you kill them outright. To cut to the chase, in late August a paper – Divergent Whole-Genome Methylation Maps of Human and Chimpanzee Brains Reveal Epigenetic Basis of Human Regulatory Evolution (pdf, supplemental data) – came out comparing levels of methylation, concentrating on the brain, between humans and chimpanzees. They found differences, particularly in regions apparently associated with diseases that we suffer from more than chimps do. Here’s a figure stolen from their supplemental information:

"The mean fractional methylation levels (± S.E.) of different genomic regions." (From page two)

“NS” stands for “not significant,” but the ones with stars are. Something to note with that graph is that there is a hidden 20% below the axis, so the differences are not quite as large as they would appear. Continue reading

Give it Up, Scientists!

The actual title of Thomas’ article for August 6 is Useless Search for Evolution of the Human Brain, but the sentiment is clear. Now, I’m sure we can all agree that if you’re going to publish an article slighting an entire area of scientific study as “useless,” putting it out 30 minutes before a 1-tonne car rockets down onto the surface of another planet ranks high on the list of worst possible moments. But then again ignoring the rover completely may well be their best option there.

Thomas begins his poorly-timed article with:

Evolutionary scientists do not know how the human brain’s ability to process language supposedly evolved from a non-speaking ancestor. Recent technological advances have enabled scientists to explore this subject in new ways, and one researcher’s review reveals two flaws that underpin the whole research effort.

Todd M. Pruess’ article (which is both open access and quite informative) actually suggests a new experimental paradigm. Continue reading