Diversity and Origins of Cattle

Introduction:

It is thought that modern cattle were domesticated from a single wide-ranging Pleistocene species, the wild aurochs Bos Primigenius, which was distributed throughout Europe, Asia and North Africa. However, the details have been hard to discern as it is difficult to distinguish the domestic breeds (B. taurus in Africa and Europe, B. indicus in Asia) from the wild progenitor archaeologically.

Phylogenetic analysis of mitochondrial DNA has indicated not only a deep split between an Asian and an African-European cluster, but also a shallow split between African and European cattle, suggesting three separate domestic events. It is still not clear, however, whether or not all European cattle are derived from stock domesticated in Western Asia, as is the case with ovicaprids and some cereals.

The origins of Bos lineages:

The European B. primigenius sequences cluster slightly more closely with extant European cattle, and certainly with taurine cattle rather than B. indicus. Extant B. taurus and B. indicus may be cross-bred to produce viable offspring. As B. primigenius and B. taurus are phylogenetically more closely related it seems likely they could have inter-bred and as such should be considered a single species (Bailey et al., 1996: 1471).

The novel sequences obtained from Pleistocene samples suggests that there was a diverse population of aurochs in the Pleistocene (Bailey et al., 1996: 1471).

Neolithic expansion of Bos:

Bailey et al (1996) estimate a minimum expansion time of 3500-4700 Ma BP, but these values are associated with a large margin of error. An expansion may have been caused by the introduction of modern farming methods, the establishment of cattle breeds, the introduction of farming in the Neolithic or as a result of post-glacial environmental change.

The lack of clustering by breed and lack of distinction between beef and dairy cattle suggests haplotypes pre-date modern farming methods and breed establishment. The presence of closely related haplotypes in the medieval period suggests the expansion took place before this, and a similar haplotype from Bronze Age Egypt may suggest it takes place even before this date. The existence of this haplotype is consistent with an origin for the European expansion in the vicinity of the Middle East and indicates that Egyptian cattle at this stage shared elements of the European gene pool. Overall, this points to a Neolithic origin for the European expansion. An alternative explanation, however, is that the expansion was not human-facilitated, but by post-glacial environmental change.

The occurrence of long-branch lineages predominantly in the European island populations suggests there may have been inclusion of local aurochsen amongst domesticates in Northern Europe. The diversity of insular cattle is twice as great as that of Continental breeds, implying a greater time-depth on the continent.

The levels and patterns of mitochondrial diversity do not point towards a single Near Eastern origin for African and European cattle within the 10,000 year time frame of domestic history. Instead it is most suggestive of two domestic origins that were either temporally or spatially separate and that involved divergent strains of taurine progenitors. This is consistent with a Near Eastern origin for European cattle and an African origin for the breeds of that continent. The dating of the putative African population expansion, although a rough estimate, seems older than that deduced in European patterns of variation. This provides tentative support for an earlier and possible Saharan domestication process that may have been independent of the later Near Eastern influences, which are detectable through the presence of ovicaprid herding (Bradley et al., 1996).

References:

Bailey, J.F, Richards, M.B, Macauley, V.A, Colson, I.B, James, I.T, Bradley, D.G, Hedges, R.E, and Sykes, B.C. 1996. Ancient DNA suggests a recent expansion of European cattle from a diverse wild progenitor species. Proceedings of the Royal Society of London B 263: 1467-1473.

Bradley, D.G, MacHugh, D.E, Cunningham, P and Loftus, R.T. 1996. Mitochondrial diversity and the origins of African and European cattle. Proceedings of the National Academy of Science, USA 93: 5131-5135.

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