There are about 1.3 billion cows in the world today. That makes just a bit of a change from 10,500 years ago, when the first population of domesticated cattle was likely just eighty head. That’s the new finding from a team of British, French, and German researchers, who extracted DNA from cow bones found at an Iranian archaeological site that dates to not long after the domestication of cows.
They discovered that the differences between these ancient DNA sequences and those of modern cattle were so minute that the only way to explain them would be if the original cattle population was extremely small, with about 80 cattle the most likely number. As the researchers explain in Molecular Biology and Evolution, since the domestication process was spread out over a thousand or so years, that’s the equivalent of only adding two new cattle each generation.
Eighty initial cattle would have given their human breeders pretty much no margin for error in terms of maintaining genetic diversity, and yet the billion cows alive today reveal just how remarkably well they succeeded in growing the population. The fact that all cattle seemingly descend from a single domestication event is also unusual—for most other domesticated animals like horses or dogs, there’s good evidence to support multiple domestication events, even if some lineages ultimately died out. But we know from the analysis of the ancient Iranian cattle bones that all cows throughout history likely only came from this one population.
The reason for all this is likely that the wild ancestors of cows, known as aurochs, were nearly too wild to domesticate at all. Though the archaeological record makes it clear that aurochs roamed throughout Europe and Asia, it seems that either most domestication attempts failed or most people just thought the better of trying to tame these creatures.
Source: Alasdair Wilkins, DNA Reveals That Cows Were Almost Impossible to Domesticate, IO9 (Mar. 28, 2012).