Climate change is one of the most pressing issues of our time. It’s also one of the most complex, and scientists are still learning new things about it all the time. One thing that is becoming increasingly clear, however, is that climate change impacts humans and the way we live. This is true today, as it was in the past. Climate change has influenced human evolution and has played a role in shaping the way we are today.
However, a key question remains. How did climate change impact early humans?
I started the North of Kuruman Palaeoarchaeology Project to address precisely this. I look to Africa because the first members of our species, Homo sapiens, emerged there, and I focus on the southern Kalahari Basin because much less is known about early humans in arid interior environments than in other kinds of environments. The team is inter-disciplinary and global, because a diversity of perspectives and expertise is the best way to tackle tough questions like this. And, to positively impact the next generation of researchers, the project supports student-led research projects in both Australia and South Africa.
In a paper published by PLOS ONE, we report new results that reveal the impact of water availability on early humans. The authors include researchers from Australia and South Africa at Griffith University, the University of Queensland (Project co-Director Benjamin J. Schoville), the University of Melbourne, and the University of Cape Town. We used a combination of archaeological and geochemical techniques to investigate how early Homo sapiens responded to changes in the local environment.
Archaeological sites preserve evidence for past human behaviors. Estimates of past temperature and rainfall can sometimes be extracted from caves, lakes, dunes, and other geological features. The best scenario is when the archaeological record and the palaeoenvironmental records come from the same locale and can be precisely dated.
This scenario is rare across much of the African continent, and particularly in the more arid interior regions.
In a paper published by PLOS ONE, we report results from one such locale.
Ga-Mohana Hill in the southern Kalahari, South Africa provides detailed records of both human behavior and paleoenvironment. Ga-Mohana Hill has revealed some of the world’s earliest evidence for innovative technological behaviors – the collection of non-functional objects and container technology; a result that we reported previously in Nature. Ga-Mohana Hill also has a datable record of past environment preserved in the form of abundant tufa deposits.
Thus, Ga-Mohana Hill provides a valuable opportunity to investigate the impact of climate change on human evolution.
Tufa deposits can be thought of as springs, waterfalls, and ponds that have turned into rock. As water evaporates, it can leave behind a calcium carbonate precipitate, forming a porous rock we call tufa.
We can find out how long-ago tufa formed using a method called uranium-thorium dating. Tufas in general have been considered too porous and ‘dirty’ for this method to be applied effectively. However, this study is adding to the growing body of research that proves otherwise.
PhD candidate Jessica von der Meden at the University of Cape Town, and first-author of the study published in PLOS ONE, carried out the extensive survey program across the landscape at Ga-Mohana Hill, documenting and sampling the variety of tufa deposits.
Ga-Mohana Hill has spiritual significance for the local communities. Out of respect for this, Jessica adopted a low-impact sampling approach, with targeted samples carefully chosen in inconspicuous locations.
Jessica discovered she could reliably date the tufas at Ga-Mohana Hill by specifically targeting ‘cleaner’ layers within the tufa formation. The method used for this is called laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), which in a nutshell uses laser technology to measure the relative amounts of uranium and thorium along a small transect. Layers in the tufa that have high uranium levels and low thorium levels are better for dating, and so once those layers are identified they are then sampled for dating analysis.
The Isotope Geochemistry Group at the University of Melbourne and Dr Robyn Pickering (University of Cape Town) helped develop the laser ablation and uranium-thorium approach, and trained Jessica on these procedures. The approach used here is a significant methodological advance for the science of dating geological formations, and to the best of our knowledge, this is the first application of its kind to tufa samples.
Our results show five tufa formation episodes dated to between 114 thousand-years-ago and 3 thousand-years-ago. Three of these tufa episodes are coincident with the archaeological units at Ga-Mohana Hill that date to ~105, ~31 ka, and ~15 thousand years ago.
Together these data when combined with that from other nearby local records, show that in the southern Kalahari, from ~240 ka to ~71 thousand-years-ago wet phases and human occupation are coupled. That is, humans chose to live in this region during periods with the climate tended to be more humid and appear to have been absent when the climate tended to be drier.
However, this isn’t the case in more recent times. By the Last Glacial Maximum (around 20 thousand-years-ago) humans occupied this region of the southern Kalahari despite evidence for drier conditions. And this timeline may even extend back to 31 thousand-years-ago, though we are limited by the resolution of the dating methods available to us to confidently assert this at this time. Future research can help pinpoint the earliest evidence for humans occupying an arid Kalahari.
The study we conducted also showed that this region of the southern Kalahari was relatively humid for much of the period between ~71 and 31 thousand-years-ago. This is interesting as this time period (called Marine Isotope Stage 4) is known at the continental scale to be relatively dry. Furthermore, despite the wet conditions, no evidence for human occupation is yet known at or near Ga-Mohana Hill.
In Africa, climate change has been a major driver of human evolution, but the precise nature of this relationship has not been established.
Our research adds important information to what is developing as a complex, multi-factorial picture of early human-environment interaction. It shows that simple stories about humans only occupying arid regions when they were humid are inaccurate.
Our evolutionary history was rich and complicated, and we can only truly understand it by looking for and investigating linked records of both human behavior and paleoenvironment, like what we discovered at Ga-Mohana Hill.
By studying the details of this relationship at early Homo sapiens’ sites in Africa, we can learn how our species adapted to changing environmental conditions in the past. Ultimately, this can help us understand what climate change means for our future.
VIDEO
Published in Nature in 2021, Dr Jayne Wilkins from Griffith University’s Australian Research Centre for Human Evolution led an international collaboration which found evidence far from coastal sites of the complex symbolic and technological behaviours that define modern humans, stretching back 105,000 years.
Dr. Jayne Wilkins is an ARC DECRA Research Fellow with the Australian Research Centre for Human Evolution (ARCHE) at Griffith University. Her research investigates the origins and evolution of Homo sapiens. Through archaeological excavation and lithic analysis, Wilkins is identifying important drivers behind our species’ enhanced capacities for social learning, sociality, and adaptability. She currently leads North of Kuruman Palaeoarchaeology Project, which is a multidisciplinary study of Pleistocene hunter-gatherer adaptation in the Kalahari Basin, southern Africa. Much of world’s earliest evidence for the emergence of Homo sapiens has been discovered in South Africa. Wilkins’ team has made significant contributions to this field, recently reporting new evidence in Nature for innovative behaviours 105,000 years ago in a wetter Kalahari.
Her interdisciplinary, international team includes researchers from eight institutions across Australia, South Africa, Canada, Austria and the UK. Local South African collaborators with the University of Cape Town’s Human Evolution Research Institute play an especially crucial role, and the project actively engages with local Kalahari communities.
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