Hominin

How does hominin evolution impact our daily lives – what the hell is a hominin? We are hominins. Hominoids are the branch of primates that includes all the past and present species of lesser and great apes. Hominins are all the species in the Homo sapiens’ lineage after the split with a common chimpanzee and bonobo ancestor between 6 and 7 million years ago (mya). For a summary of hominin evolution, see Overview of Hominin Evolution by The Nature Education Knowledge Project. So, how does hominin evolution impact our daily lives – what the hell makes Homo sapiens so different from other primates? The number of people who don’t know what separates Homo sapiens (modern humans) from chimpanzees and bonobos (our closest relatives) always shocks me. Here are some hints: teeth, brain, and walking upright.

There are a lot of physiological differences between chimpanzees and humans, but the big differences are skull shape and size for protecting the brain and chewing, and the musculoskeletal features associated with bipedal locomotion (walking upright on two legs). Over time, parts of the skull became smaller to support smaller teeth due to changes in diet; parts of the skull became bigger to support a bigger brain; and the musculoskeletal system changed to support bipedal locomotion instead of quadrupedal (walking on all fours). These are the major anatomical changes that paleoanthropologists look for when classifying species in the hominin lineage. It’s difficult work because the remains of some species are extremely sparse like the partial femur of Orrorin tugenensis. However, this femur fragment provided enough information to suggest that this hominin relative from approximately 6 mya was walking upright.

Back in 2002, a research team led by Martin Pickford took a very close look at the Orrorin tugenensis’ femur. Pickford’s team discovered that the femur had the shape, density, and wear patterns associated with walking upright. Before this discovery, upright walking was thought to have occurred around 4 mya. Pickford’s discovery pushed that date back to 6 mya; there is speculation that upright walking might even be older. We’ve been walking for a very long time. So, without interruption, how does hominin evolution impact our daily lives? It impacts our daily lives by setting us up for success or failure, in the Darwinian sense.

A recent hypothesis by David Raichlen and Gene Alexander from the University of Arizona suggest that the long human lifespan, when compared to other primates, is a result of aerobic physical activity in response to the apolipoprotein E (APOE) ε4 allele. The researchers gathered evidence from neuroscience, anthropology, and brain-imaging research to develop their hypothesis.

The APOE ε4 allele, found in 15 percent of the population, has been linked to increased cholesterol levels, and an increased risk of Alzheimer’s disease, cardiovascular disease, and mortality. The APOE protein is found in plasma and the central nervous system and aids in regulating cholesterol, lipid metabolism, and repairing cells. According to Raichlen and Alexander, recent research suggests that physical activity mediates the ε4 allele’s potentially harmful effects.

Raichlen and Alexander proposed that an increase in physical activity around 1.8 mya also increased our ancestors’ chances of survival. This time period coincides with the emergence of Homo erectus. The authors suggest that H. erectus invested heavily in hunting and gathering for survival, which requires a high level of aerobic endurance. Raichlen and Alexander point to paleoanthropological reconstructions of earlier hominin species to show that their behaviour was more ape-like and sedentary before H. erectus. Therefore, a high level of aerobic endurance was a major contributing factor to hunting and gathering success, which, in turn, became a desirable trait for genetic success and also reduced the potentially harmful effects of the APOE ε4 allele. Furthermore, by reducing the potentially harmful effects of the APOE ε4 allele, Raichlen and Alexander suggest that the increase in aerobic endurance also contributed to an increase in lifespan. The authors looked at research that found that H. erectus had an estimated lifespan of 60 years. This is 20 to 30 years longer than earlier species. However, Raichlen and Alexander recommend caution when estimating age from the fossil record due to the processes acting on hominin remains of this antiquity.

Around 200 kya APOE ε2 and ε3 alleles appear in the human genome. Carriers of these alleles have lower cholesterol levels and a reduced risk of Alzheimer’s disease, cardiovascular disease, and mortality. In modern humans, these alleles are found in six percent (ε2 allele) and 78 percent (ε3 allele) of the population. Raichlen and Alexander argue that this recent change in the human genome would have contributed to further lifespan increases seen in Upper Paleolithic and modern human populations. The authors conclude that, “Without a continued lifestyle of high physical activity, regions of the world where the ε4 allele remains highly prevalent (e.g., equatorial Africa with ε4 frequencies approaching 50%) may experience a substantial increase in CAD [coronary artery disease], AD [Alzheimer’s disease], and dementia with the increasing globalization of sedentary lifestyles.”

Hominin evolution impacts our daily lives by setting us up for success or failure. Our bodies are a direct result of natural selection and adaptation: bipeds who favour aerobic endurance. We have adapted to live healthy long lives as long as we are active on a daily basis. When we go against millions of years of successful adaptations by adopting sedentary lifestyles, we increase our susceptibility to a wide range of diseases. So, show some respect for your hominin ancestors and move your body.

Rodney Steadman 11 June 2014

Works Cited

Pickford M, Senut B, Gommery D, & Treil J (2002). Bipedalism in Orrorin tugenensis revealed by its femora Comptes Rendus Palevol, 1 (4), 191-203 DOI: 10.1016/S1631-0683(02)00028-3

Raichlen D, & Alexander G (2014). Exercise, APOE genotype, and the evolution of the human lifespan Trends in Neurosciences, 37 (5), 247-255 DOI: 10.1016/j.tins.2014.03.001

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