Sunday, 8 July 2018

The genetic scars of our insect-eating, egg-laying past - the powerful genomic evidence of common descent

The earliest mammals are believed to have been insect-eaters, which means that they would have had the genes for chitinase, an enzyme that digests chitin, the polysaccharide which is the main component of insect exoskeletons. Given this, common descent would predict that non-insectivorous mammals, which no longer need to digest chitin, would no longer have functioning chitinase genes, but instead have chitinase pseudogenes as inherited remnants of their insect-eating past.

Recently, Christopher Emerling, Frédéric Delsuc, and Michael Nachman published a paper in Science Advances in which they showed that in all the carnivorous and herbivorous animals whose genomes they examined, they found not only chitinase pseudogenes, but in animals previously known to share common ancestry, they found exactly the same mutations in some of the chitinase pseudogenes.

Regular readers of the website will be well-aware of the power of this argument; shared identical genomic 'errors', be they pseudogenes, endogenous retroviral elements, or retrotransposons are some of the strongest lines of evidence confirming common descent. Just as shared identical sections in exam papers confirm copying and cheating in students (identical independent errors are of course so unlikely an explanation as to be readily dismissed out of hand), so do shared identical genetic errors confirm the inheritance of a 'broken' genomic elements from a common ancestor of the species examined.

Similar evidence can be found from examples such as broken egg yolk protein genes in placental mammals, broken olfactory receptors in aquatic mammals such as whales, broken tooth-enamel genes in toothless animals, and the broken vitamin C synthesising gene GULO in humans and primates. These previously-mentioned examples made the case for common long ago, but papers such as this are invaluable if only to show the power of evolutionary theory in its ability to make predictions, and explain facts.

Sunday, 1 July 2018

Removal of Francisco Ayala book from "Recommended Reading" List

Geneticist Francisco J. Ayala's book "Darwin's Gift to Science and Religion" was in my list of recommended reading, but after an investigation found he had sexually harassed both faculty and graduate students, I have removed it from the list. Citing articles written or co-written by Ayala - who prior to this was a highly-respected geneticist - is one thing, but I don't feel comfortable recommending a book he has written in the light of this revelation.