A team at the University of Veterinary Medicine, Vienna, has discovered that nearly all today’s horses* trace tail-male back to Arabian and Turkoman stallions brought to Europe over the last seven centuries (yes, pre-thoroughbred). There is so little diversity in domestic horses’ Y chromosomes that it took an advance in research methods to be able to distinguish between the limited lines out there. Researchers will even be able to designate haplotypes for single stallions, which is how they discovered the Turkoman great great great great great great (times a few more) grandsires of today’s thoroughbreds. Here’s a link to their research.
The fact that in modern times we humans chose to use a small number of stallions to improve our horses makes an interesting contrast to a study published in April on the early years of horse domestication (from 3,500BC on). When I was working on The Age of the Horse, I believed the current research, which suggested that very few stallions were involved in the process of turning wild horses into stockier, faster, more colourful and higher milk-yielding domestic horses. The study team revealed that the opposite was true. In fact, we began our working relationship with horses with plenty of stallions and lots of Y chromosome and haplotype diversity. You can see the study here. Then the bottleneck narrowed as we discovered intensive breeding and those fancy Oriental stallions.
*I would be curious to know which modern breeds were used in this study. Would the results be different for Mongolian horses?