Teeth of hominids suggests early cavemen had ‘foreign brides’
1 June 2011
Scientists have unlocked more secrets about our evolutionary past by using new techniques to extract information from the fossilised teeth of our ancient human ancestors. By testing the tooth enamel of 19 hominids found in cave sites in South Africa, a new study involving researchers at the University of Oxford provides surprising evidence of how individuals dating back more than 2 million years once lived.
The study, published in the latest issue of the journal Nature, suggests that female hominids moved from the place where they were born and spent their childhood, while male hominids preferred to stay within close range of home. This pattern of female dispersal can still be observed in chimpanzees and bonobos, but is unlike other primates including gorillas, which have harems dominated by one male with young males needing to leave the family group.
The international research team tested the fossilised teeth dated from 2.4 to1.7million years ago from two australopith species – eight Australopithecus africanus individuals and 11 Paranthropus robustus individuals. The researchers found only about ten per cent of the male hominid teeth were from outside the range of their local area, compared with more than half the female teeth indicating that the males stayed close to home.
The teeth were from the Sterkfontein and Swartkans cave sites in South Africa, two archaeologically significant sites in hominid evolution. Testing was done using strontium isotope analysis of tooth enamel, a technique which provides evidence of where an individual lived when the tooth formed. Strontium, a naturally occurring element in rocks and soils, is absorbed by plants and animals, and can be found in trace amounts in mammalian teeth. Strontium isotopes reflect the particular geological conditions so even small traces can be revealing of that individual’s location. Minute quantities of strontium were analysed using a relatively new ‘laser ablation’ technique, which leaves the enamel surfaces of the teeth practically undamaged.
The researchers were able to distinguish the teeth of the male from the females by comparing the size of the individual molars as the male hominids were larger than the females. Why the males preferred to stay close to the cave sites is unclear. The study suggests that perhaps the males preferred the vegetation or a landscape dominated by dolomite rock where there would have been an abundance of caves.
Researcher Professor Julia Lee-Thorp, a specialist in isotopic analyses of fossil tooth enamel from the Research Laboratory for Archaeology and the History of Art at the University of Oxford, said: ‘Our earlier carbon isotope projects showed us that these hominids had highly variable diets. We wondered if that implied that they moved about on the landscape a good deal. As the numbers rolled off the mass spectrometer after each laser ablation we were at first disappointed. But we soon realised that we had found another prize – a difference between the males and females. It was totally unexpected.
Studies like these really bring home that finding and describing fossils is not the end of the story. Thoughtful application of these new analytical methods can tell us such a lot more about the details of lives in the distant past.’
The University of Oxford collaborated with a team of researchers from the United States, South Africa, Switzerland, and Germany. Lead author Sandi Copeland said: ‘One of our goals was to try to find out something about early hominid landscape use. Here we have the first direct glimpse of the geographic movements of early hominids. We assumed more of the hominids would be from non-local areas, since it is generally thought the evolution of bipedalism was due in part to allow individuals to range longer distances. Such small home ranges could imply that bipedalism evolved for other reasons.’
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