Evolution Update

Evolution Update

Dispersal of Early Hominin from a Topological Approach

Irma Shaboian November 29, 2015

The landscape of terrestrial surfaces is likely to be the driving force that led to bipedal locomotion of early humans and their dispersal from Africa.

The prevailing out-of-Africa theory as the origin of our hominin species focuses on the dry savannah environment of Africa as the starting point for early humans beginning to walk on two legs (bipedalism) and its ensuing cognitive developments. The belief that our early ancestors amended to their settings in order to survive neglects factoring in climate change and how that affected our species’ early environment thereafter.

The advantages afforded by bipedalism, such as tool making and wandering the earth, to the early Homo genus have been been attributed to the variability of the climate. More clearly stated: the changing climate was key in causing early humans to adapt to its consequences, like food availability and rainfall. On one hand, it could be argued that the changing climate sheds light on how humans consequently adapted to changing environments, while on the other raising the question on what was the driving force behind human dispersal from East Africa. Unless, of course, early humans were wandering to where the climate and vegetation were more suitable to their needs.

In a preliminary analysis, Dr. Isabelle Winder from University of York in the UK accounts for how plate tectonics and subsequent landscape formations provided the corridor for bipedalism and early dispersal. Published in the Journal of Human Evolution, her team proposes the complex topography hypothesis. Herein, Dr.Winder argues that it is the dynamic nature of unstable landscapes that create land surfaces and have irregular morphology or ‘roughness’ due to shifting tectonic plates, earthquakes, or volcanic eruptions. That said, her research proposes that it was the topographic conditions that promoted early human expansion into new territories, which were not dependent on vegetation or climate.

According to her team’s hypothesis, an irregular terrain would provide a tactical advantage from predatory protection and acquiring food supplies. For instance, earthquakes on fault zones were able to trap water and thereby renew water supplies, or elevated landscapes provided opportunities for monitoring prey. In other words, the mixed roughness of the terrain allowed for variable environmental characteristics and our ancestors migrated along such paths.

To test the hypothesis, digital elevation models (DEMs) were used to map complex landscape features as they might have existed during the Pleistocene epoch using satellite data. Features that were considered ‘rough’ like mountain ranges, low ridges, and other surface irregularities were included in the data. Using known fossils that had been associated with early human activity, vegetation, and climate were used to create an idea of the landscape distribution. It is known that during the Pleistocene epoch, about 1.8 million years ago, the most recent Ice Age occurred wherein there were interglacial warming periods. More notably, the northern hemisphere was more affected by glaciation than the southern, where the climate was mostly tropical, subtropical, or humid.

Amongst the findings include a nearly continuous chain of landscape ‘roughness’ in Northern Africa, particularly towards the eastern margin that connects Africa to Arabia, Eurasia and the rest of the world. While these were predictive models, it is likely that climatic factors afforded during the Pleistocene epoch made dispersal likely to follow trajectories that included changes favourable for early hominin settlement. For instance, differing sea levels and land elevations.

The complex topography model, as demonstrated by the research findings, helps explain why migration trajectories were non-random and contained. With experience surviving in various topographies, the early Homo could better adapt to newly encountered ones. It becomes inferable that early humans migrated and expanded into regions with comparable landscapes that were advantageous for their survival instead of migrating to climatically preferred ones. This is because, of course, climatic and subsequent environmental factors were dependent on tectonic factors like mountains. It could then be understood that as the landscape changed, the climate and environment followed, with early hominin close behind.

Today a different picture could be painted. Anthropogenic impacts through fracking for oil has the potential to trigger human-made earthquakes the way that tectonic activity does naturally, while the burning of fossil fuels pollutes the air like volcanic smoke does. Given the way that human evolution was steered under the influence of topography and climatic effects concurrently, it will be interesting to observe the role that human activity plays as it influences topography and climate both simultaneously and separately.

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