The NOVA series “Becoming Human” http://www.pbs.org/wgbh/nova/beta/evolution/bec

Question

The NOVA series “Becoming Human” http://www.pbs.org/wgbh/nova/beta/evolution/becoming-human-part-1.html (this web site will allow you to watch the episodes online i) describes the discoveries of several different fossilized remains found in Africa of human ancestors. These discoveries are changing the way scientists think about the evolution of our species from ape like ancestors. It is becoming clear that the earth and specifically the African rift valley, a few million years ago, was going through severe climate changes. In part I of the “Becoming Human” series, new discoveries are described that shed light on when the ability to walk upright (bipedalism) occurred as well as when the development of larger brains occurred. These events are correlated with new research in the African environment that suggest changes occurred that provided the selective pressures for these new traits. In part II there is new evidence about when humans became essentially hairless and the selective advantage for this change. In part III there is new evidence describing the evolutionary relationship between humans and neanderthals as well as DNA evidence suggesting that neanderthals likely had the ability of oral communication.

For your post, choose one of the discoveries above, (bipedalism, or brain size, or hairlessness, or relationships with neanderthals) or another trait of your choice and describe the selective pressures found in the environment that might have attributed to its development. Do some additional research on the web to determine if the views presented in this NOVA series regarding the trait of your choice are supported by other scientists or do others scientists disagree. Moreover, can you see any parallels or lessons that relate to the climate changes we see right now and the future of human evolution? Finally, comment on whether the research presented in this NOVA series change your view of the theory of evolution. Does it provide further support for the theory or does it call into question the validity of the theory as a whole?

Explanation / Answer

I will take up selective pressures found in the environment that might have attributed to development of hairlessness.

There was a positive selection pressure that attributed to hairlessness. 8 million years ago hairy Homo species existed. These were land mammals and the hair provided insulation to their body from severe cold and heat. After this aquatic mammals evolved. Now, the hairy feature was not an advantage inside water, because hair will not provide insulation in water. So, slowly and steadily hair follicle cells came into dormant phase and led to evolution of hairless mammals.

Those mammals, i.e. hominids that stayed on land and were upright spend most of their time in sun unlike their ancestors who dwelt in shady forests and walked on four toes. So, in sun, excess heat is there and the presence of hair overheated their body. So, they evolved to have hairless bodies.

One more point of consideration is that parasitic attack will be higher on a hairy body in comparison to hairless body. So, body's defense system also favoured positive selection towards hairless body.

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