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Cattle call
Natural History, May, 2003 by James J. Moore
Daniel G. Bradley concludes that British aurochs did not interbreed with early domestic cattle ["Genetic Hoofprints" 2/03]. But that assertion overlooks that fact that (especially early on) domestication is a social as well as a biological process. Calves born to tame mothers living with humans would either prove tractable and so be kept to breed, or intractable and so escape or be eaten, outcomes that are genetically equivalent. Tractable calves born to wild mothers would only be captured and tamed with some effort; because the early inhabitants of Britain already had domestic cattle, few farmers would have bothered.
In short, a one-way "filter" would be applied to nuclear genes, which Mr. Bradley's work on mitochondrial DNA could not detect. Wild aurochs bulls breeding with domestic cows would contribute nuclear genes, but no mitochondrial genes, to early cattle; as long as such domestic cows gave birth and raised their calves near humans, their calves would likely join the domestic herd.
James J. Moore University of California, San Diego La Jolla, California
DANIEL BRADLEY REPLIES: James Moore highlights an important limitation that applies to all genetic evidence based on one marker system: different genes can represent different strands within the history of a population and thus tell different histories. In fact, cattle studies present one of the best examples of uncoupling of maternal and other ancestral strands. The massive influx of Bos indicus genes into African cattle seems to have left no maternal legacy: the mitochondrial genes in African cattle seem to have remained B. taurus.
Thus I agree that the study of mitochondrial variation alone cannot eliminate the possibility that ephemeral encounters introduced nuclear DNA from British aurochs into the domestic gene pool. Studies of other marker systems, particularly the Y chromosome, will clarify that question. In fact, however, our preliminary data from modern British cattle with Y markers have not revealed any traces of divergent chromosomes that might indicate substantial wild male input.
COPYRIGHT 2003 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning
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