by Matthew Cobb
This blog normally (and rightly) gives pride of place to cats, but this post will be about dogs. I trust Jerry will forgive me when he returns.
Hidden away in the same issue of Science that deals with Ardi, there’s an article by a host of researchers from the US and France (you’ll need a subscription to get past the abstract), looking at the genetics of dog coat variation. Amazingly, it turns out that most of the massive range in coat phenotypes we can see between “pure breeds” and mongrels can be accounted for by mutations in just three genes. (If I were one of the authors, I’d be pretty peeved – all the media attention will be focused on Ardi; in a “normal” week, they could be sure of making the TV, press and radio…)
The authors studied three characteristics of the canine coat: (i) the presence or absence of “furnishings” (growth pattern marked by a moustache and eyebrows seenin wire-haired dogs); (ii) hair length; and (iii) the presence or absence of curl. To find the genetic bases of these characters, they created three genome-wide single-nucleotide polymorphism (SNP) data sets, based on a) 96 dachshunds showing three coat varieties (wire-haired with furnishings, smooth, and long-haired without furnishings); b) 76 Portuguese water dogs showing the curl phenotype and c) 903 dogs from 80 breeds representing a wide variety of phenotypes.
They found that variability in three genes, coding for R-spondin–2, fibroblast growth factor–5, and keratin-71, accounts for most of the different kind of coats that can be observed (“these three mutations in various combinations explain the observed pelage phenotype of 95% of dogs sampled”) . They summarise their findings in the following figure:
Interestingly, they conclude “None of the mutations we observed were found in three gray wolves or the short-haired dogs, indicating that short-haired dogs carry the ancestral alleles (table S1). Our finding of identical haplotypes surrounding the variants in all dogs displaying the same coat type suggests that a single mutation occurred for each trait and was transferred multiple times to different breeds through hybridization.”
However, although they open their article by pointing out that dogs and humans have lived together for around 15,000 years, they point out in their conclusion that dog “breeds” are an incredibly recent invention – less than 200 years. Inother words, in a couple of hundred year, artificial selection on just three genes has produced an incredibly variety of phenotypes. Furthermore, that selection may have focused on different characters, such as aggressivity or size, the genes for which may be linked to the coat genes. They conclude, “Consequently, in domesticated species, the appearance of phenotypic complexity can be created through combinations of genes of major effect, providing a pathway for rapid evolution that is unparalleled in natural systems.”
This, of course, was also Darwin’s insight (although he did not put it in these terms). Artificial selection by 19th century breeders provided him with the key to understanding natural selection as the force that could generate apparently directed evolutionary change. And that is a much more powerful explanation than anything the creationists can come up with.