Why detecting hybrids in the Homo fossil record is so difficult – a lesson from howler hybrids
Apologies, I have been away from the blog for a while as I have been finishing up my Master’s degree! I should be back to publishing regularly form this point forth.
Now, to the topic at hand.
An interesting piece appeared in the American Journal of Physical Anthropology this month relating to hybridisation between two holwer monkey species, and the difficulty of identifying these hybrids on visual characteristics alone (morphology). In short, the morphology of these hyrbidised individuals does not correspond directly with the level of admixture present in genetic terms. For example, an individual with, say, one parent that was a first generation hybrid and one that was a non-hybrid, will not exhibit a 25/75 split in its morphology; it is more likely to simply appear to be a typical member of the species that has contributed the most genetic material.
This finding is interesting when we consider the argument surrounding the possibility of interbreeding between species of Homo in the Middle and Late Pleistocene. In essence, from a genomic perspective interbreeding seems to have been very likely, with both Homo neanderthalensis and the still mysterious Denisova hominin having made measurable contributions to the modern human genome. On the other hand, fossil evidence of anything that could decidedly be called a hybrid is virtually non-existant (virtually as there are some odd crania about from the Late Pleistocene that have raised hybrid questions, for example ‘the child of Lagar Velho’). Considering what was found in the piece mentioned above (full citation below) this lack of fossil evidence actually seems rather logical (not that we were expecting to find an abundance to begin with), as any hybrid individuals of anything other than a first generation cross would be likely to resemble one parental species so greatly as to render any talk of hybridisation moot.
Are palaeoanthropologists chasing phantoms in looking for some kind of ideal hybrid? I say likely yes.
Kelaita, M. A. and Cortés-Ortiz, L. (2012), Morphological variation of genetically confirmed Alouatta Pigra × A. palliata hybrids from a natural hybrid zone in Tabasco, Mexico. Am. J. Phys. Anthropol.. doi: 10.1002/ajpa.22196