Domestication of horses

Przewalski's horse - no longer seen to be a direct
ancestor of domestic breeds. Photo by Chinneeb (CC)
 

A large consortium has just reported on the genome of horses (Equus caballus) from the Siberian permafrost (here). The two specimens were estimated to be 16 and 42 thousand years old. Thus they were from before the start of domestication as known from the archeological evidence.

Horse phylogenetic relationships from Schubert et al. (here)
(c) The Authors

The phylogenetic analysis showed as expected that the ancient specimens (purple) are basal to all living members of the E. caballus species. However, while most genes present in domesticated breeds were found in the ancient genomes, many were missing from the Przewalski horse genome. It is perhaps a distant cousin rather than a direct ancestor of the domesticated horse (see commentary here).

Section through umbilical cord of Przewalski's horse
From the Benirschke web site (here)

So there have been two paths of selection: one through selective breeding (resulting in both desirable and deleterious traits) and the other through natural selection resulting in Przewalski's horse.

 

Placenta and implantation site of Przewalski's horse.
From the Benirschke web site (here)

These conclusions are in line with those made after sequencing the genome of a really old horse from the Middle Pleistocene (see previous post).