Far from home: new research on human evolution
Dr. Vaughan Grimes with the laser ablation multicollector inductively coupled plasma mass spectrometry (or LA-MC-ICP-MS) used to get the strontium isotope data. Photo by M. Pellegrini
By Meaghan Whelan
Research with a Memorial connection has shed new light on the lives of our early ancestors. The study, published in Nature, found that female hominins were more likely to have moved from their home area and settled with a new group than their male counterparts.
Dr. Vaughan Grimes, Department of Archaeology, was part of an international research team that studied landscape usage of early hominins from the Sterkfontein and Swartkrans cave sites in South Africa. This investigation was made possible by employing scientific techniques that are relatively new to archeological study.
"Archeological research falls on the border between arts and science. Scientific tools, such as strontium isotope analysis and laser ablation multicollector inductively coupled plasma mass spectrometry (or LA-MC-ICP-MS), can help us answer questions about human evolution and behaviour," Dr. Grimes explained.
Strontium is an element that is found in rocks, but gets incorporated into plants and eventually the skeletal tissues (bones and teeth) of humans and animals via their diet.
"The strontium isotope ratios present in tooth enamel reflect the geographic location in which an individual lived during childhood. We compared the hominin tooth enamel data to the strontium isotope values found in fossil animals and modern plants from various landscapes around the cave sites and were able to determine the range of movement of the hominins."
In order to sample and analyze the enamel strontium isotopes, the researchers used laser ablation. The primary benefit of laser ablation is its almost non-destructive nature on the enamel surface – a critically important factor when dealing with such valuable samples.
"It was a privilege and honour to have access to these materials. They are very rare and it is important to preserve them for future research. Without utilizing the laser ablation method, we would never have been able to use these priceless fossils for our research."
When they analyzed the strontium isotopes in the hominin teeth, they were able to determine that smaller hominins (females) had values different than the landscape they were found in.
The research showed that there was a wider range of females leaving their home area and settling with a different group. This pattern of behaviour is typical of chimpanzees and many modern human groups, but not of gorillas or most other primates. This could be related to the selection of mates or the targeting of food resources, or could indicate that males preferred their home habitats due to the presence of caves or of preferred vegetation.
"This research gives us a more direct approach to understand how hominins used their landscape. Until now we've only had indirect methods to answer the questions of how far they travelled or how they interacted with other groups. For example, we could look at the types of stone tools or animals found with their remains and hypothesize about where they came from based on the origins of these materials, but there was no direct, concrete linkage that could be made," Dr. Grimes explained.
The isotope analysis techniques in this study can be used to address a variety of research questions in archaeology, including the migration and transhumance patterns of animals or how pioneers in colonial North America moved and settled.
"Memorial is a great place to be for this type of research," said Dr. Grimes. "In collaboration with colleagues from earth sciences, chemistry, physics and biology, the Department of Archaeology is now set up to carry out a wide range of research using isotope analysis. We have world-class infrastructure and analytical facilities at Memorial, and I'm looking forward to continuing to develop the methods featured in our paper."
Strontium isotope evidence for landscape use by early hominins was published in Nature on June 2, 2011.