Darren Naish, in his great post on the origins of the domestic dog, writes:
As a rough rule of thumb, the domesticated forms of wild mammal species (1) revert back to wild-type after being feral for a few generations, and (2) readily interbreed with their wild ancestors. If domestic dogs are wolves, then the many populations of feral dogs that live world-wide should theoretically have reverted back to being wolf-like in appearance and behaviour. But they havenâ€™t. Instead, domestic dogs always end up looking like pariah dogs â€“ the relatively small (11-16 kg), socially flexible semi-domesticated and feral dogs of the Old World tropics.
Archaeological data shows that pariah dogs have a stable history, with dog skulls from 4000 year old deposits in Thailand being essentially identical to the modern dingo-like pariah dogs of the area.
A recent post on O&P regarding Heck cattle got me thinking about this point. For those who don’t want to click through, Heck cattle are an attempt to breed back to the extinct ur-cow – the aurochs. The general consensus on Heck cattle seems to be that the attempt was a failure; “once a genetic lineage is gone, it cannot be ‘bred back’”*. My thought on all this is that it seems to show that once genetic material is lost in a population (as a result of domestication) it’s gone – all the king’s horses, etc. Perhaps, then, it’s not shocking that dogs revert to pariah dogs in some number of generations – the genes that would allow reversion to a more wolfy form are just gone from the domesticated dog’s gene pool. To extend the title of the post a bit – border collies are to pariah dogs as Holsteins are to criollos/Texas longhorns? Don’t get me wrong – there are a number of other persuasive points in Darren’s post – I’m just not sure about the ‘won’t revert to wolves’ argument at this point.