House-husbands. Not so progressive after all…
A terrific paper in Nature this month used an ingenious combination of strontium isotope analysis of molars from individuals of the species Australopithecus africanus and Paranthropus robustus and comparisons of molar size as indicators of sex (much greater sexual dimorphism in these early hominins) to come to two very interesting conclusions.
1) It would appear that in our early bipedal ancestors, and indeed cousins in the case of P. robustus, it was more common for females to disperse from their place of birth and ally themselves with other ‘troops’ (for want of a better word) than it was for males. Males it would seem, enjoyed something of a ‘stay at home father’ lifestyle and had only relatively small ranges. This is in agreeance with what is seen in many modern human societies and those of our close extant relatives like the chimpanzees and bonobos (but not gorillas or other primates).
2) With the above point in mind, this challenges the notion that bipedalism evolved as a consequence of an increased need to move long distances, the so-called ‘endurance’ theories. Given my personal leanings toward the wading model put forward by Niemitz in Naturwissenschaften in 2007 and general unease with the unconvincing evidence for the endurance models I found these findings in Nature both exciting and in the best possible sense unsurprising.
There are of course other interpretations that are possible, such as the small home range being an example of a preferred habitat (cave-dwelling). If this were the case the species in question may roam further under more general circumstances but I find that unlikely. I anticipate that future evidence will support the ‘small range’ idea above as a general behavioural truth about our ancestors.
“Strontium isotope evidence for landscape use by early hominins”
Copeland, S., Sponheimer, M., Ruiter, D., Lee-Thorp, J., Codron, D., Roux, P., Grimes, V. & Richards, M.
NatureVolume: 474, Pages:76–78 Date published:(02 June 2011)