Saturday, 23 October 2021

Evolution News - Savana Chimpanzees are Showing us How Humans Evolved

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Chimpanzees walking in the savanna of Fongoli (Senegal).
Photo: U. Villalobos-Flores.
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Savanna chimpanzees in a cave in Sabe (Guinea).
Photo: Jane Goodall Institute Spain and Senegal.
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Chimpanzees at Fongoli in Senegal drink polluted water in mining pits.
Photo: J. Pruetz.
savanna chimpanzees, a model for the understanding of human evolution - Universitat de Barcelona

An international group of primatologists, co-directed by Adriana Hernández, of the University of Barcelona, Catalunya, Spain and Stacy Lindshield of Purdue University, West Lafayette, Indiana, USA, has studied the behaviour of savanna chimpanzees as a model for how the chimpanzee ancestors of hominids would have behaved at a key stage in their diversification from their common ancestor.

Although savanna chimpanzees (Pan troglodytes) are genetically identical to their forest-dwelling counterparts, they have several cultural differences that have enabled them to survive in a savanna environment which it hotter, drier and more seasonal than a forest environment. These are exactly the environmental challenges that early pre-hominid apes would have had to cope with in south and east Africa as climate change firstly isolated them in diminishing forests then stranded them in a relatively treeless landscape in which only those able to adapt would survive.

Like their modern counterparts, at least a substantial part of that adaptation was to evolve cultures which enabled them to adopt survival strategies. This in turn would then have facilitated the genetic changes which now distinguish us from our close cousins.
From the Barcelona University news release:
The study of chimpanzees in the savanna and what we call the effect of the savanna environment has important implications in reconstructing the behavior of the first humans who lived in similar habitats and therefore helps us to better understand our own evolution.

We know that early hominins adapted to savanna environments similar to those found by chimpanzees, and it is thought that savanna conditions caused adaptations in our ancestors, such as brain expansion or tolerance to high temperatures, therefore, understanding how our genetically closest relatives adapt to a dry, hot, seasonal and open environment, very similar to those where early hominins lived, helps us to analyze how our ancestors might have adapted and how the characteristics that define us as humans could have emerged.

Understanding how they cope with the heat can help us understand how the strategies that humans have to cope with the heat came about. Some are probably the same for chimpanzees and hominins, such as using caves or diving into water to cool off.

The early hominins also had to face water shortages for part of the year.

R. Adriana Hernández, Co-senior author
Department of Social Psychology and Quantitative Psychology
Faculty of Psychology
University of Barcelona, Barcelona, Spain
According to the researchers, the environmental conditions of these places would provoke a specific type of behaviors and physiological responses in these chimpanzees - such as resting in caves or digging to extract water - that do not occur in those of their congeners that live in wooded areas, where they do not they face such extreme environmental conditions.


The closest living genetically evolutionary relative to humans

Chimpanzees ( Pan troglodytes ) are the closest living evolutionary relatives of our species, sharing 98.7% of their DNA with humans and sharing an ancestor with them that lived approximately 4.5 to 6 million years ago. years. Despite this closeness, they lack some of the biological and cultural traits that humans possess to adapt to extreme heat, such as the numerous eccrine sweat glands, the relative lack of hair, or the ability to create artifacts such as containers of water. and sun hats that mitigate dehydration and heat stroke.

Chimpanzees that live in the savanna are taxonomically indistinguishable from other chimpanzees. For this reason, comparisons of behavior, morphology and ecology with those living in more forested landscapes provide key information for generating hypotheses or testing theories about how early humans were able to adapt millions of years ago as forests Africans were retreating and giving way to the savannas.


Strategies to adapt to high temperatures

Among the characteristics collected by the study, the strategies of savanna chimpanzees to tolerate high temperatures stand out… Another example that the researcher highlights are the ways in which these chimpanzees try to hydrate during the late dry season, such as digging for water when it is reduced to only a few points on the ground.
Geographic distribution of chimpanzees (Pan troglodytes)54 in savanna and forest landscapes across Africa relative to the minimum threshold of annual rainfall (Worldclim)11, 54, 264, and indicating potential new sites for future research on savanna chimpanzees.

Modified from Reference 11 under a Creative Commons Attribution 4.0 International License
As well as adapting their behaviour to cope with high temperatures and seasonal water supplies, there is another adaptive cultural change. Instead of living in small bands occupying a relatively small, densely-populated territory where essential resources are in good supply, the savanna chimpanzees have had to expand their territory from the usual 3-30 km2 to about 100 km2 with a much lower population density. Larger territories are naturally harder to defend.

The group's findings are published, open access, in the journal Evolutionary Anthropology.

Chimpanzees (Pan troglodytes) are the only great apes that inhabit hot, dry, and open savannas. We review the environmental pressures of savannas on chimpanzees, such as food and water scarcity, and the evidence for chimpanzees' behavioral responses to these landscapes. In our analysis, savannas were generally associated with low chimpanzee population densities and large home ranges. In addition, thermoregulatory behaviors that likely reduce hyperthermia risk, such as cave use, were frequently observed in the hottest and driest savanna landscapes. We hypothesize that such responses are evidence of a “savanna landscape effect” in chimpanzees and offer pathways for future research to understand its evolutionary processes and mechanisms. We conclude by discussing the significance of research on savanna chimpanzees to modeling the evolution of early hominin traits and informing conservation programs for these endangered apes.

Once again, we see biomedical scientists in no doubt that the difference between modern and ancient hominins, and how we diversified from our common ancestor with the modern chimpanzees, has an evolutionary explanation, with no hint whatsoever of a loss of confidence in the TOE to explain the processes involved in this transition that Creationists fantasise over. Consequently, we can observe bands of chimpanzees, subject to the same environmental forces that shaped our remote ancestors several million years ago and put hominins on the path that eventually led to Homo sapiens, and draw conclusions based on those observations. Also, what we can observer here is the beginnings of gene-meme co-evolution which has been a major factor in the evolution of modern humans.

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