The camel family (Camelidae) originated in the New World, but by the Middle Pliocene (about three million years ago) camels had migrated into the Old World across the Bering Land Bridge. The two-humped wild species, Camelus ferus, is generally considered to be the ancestor of the living, domestic, two-humped (Bactrian) camel, but whether the one-humped (Arabian) camel or dromedary is descended from the same or a different ancestor is a moot point. The Bactrian camel differs from its Arabian cousin not only in having two humps, but also in its shorter legs and stockier build. Moreover, differences in bone morphology underlie the different shapes of humps in Bactrian and Arabian camels, lending support to the idea that these camels are different species. Nonetheless, fertile offspring can result from crossing these two varieties. The offspring have a single, somewhat indented, long hump and are even said to exhibit hybrid vigour; but continued crossbreeding rapidly results in loss of fertility. Together, these findings suggest that the Bactrian and Arabian camels are different species with a separate ancestry.
As Peters and von den Dreisch point out2, identifying the earliest evidence of any domestic animal in the archaeological record is fraught with problems. It can be difficult to determine if artistic representations or bone remains (which are often fragmentary) represent domestic or wild camels, particularly as the earliest domesticates were anatomically very similar to their wild ancestors. Moreover, the archaeological context of the finds must be scrupulously examined. Animal remains from sites overlain with the remnants of later occupations can be unreliable as records of early camel domestication because of possible contamination by younger material. Direct radiocarbon dating of animal remains is essential.
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