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Humanity out of Africa

Genetic tracking has taken scientists back to a woman whom they describe as our common ancestor. They have given her the name Mitochondrial Eve. In male genetics there is the Y Chromosome, passed from father to son – and scientists have tracked a male ancestor to someone they call Mitochondrial Adam. The researchers have gone as far back without a break in matrilineal and patrilineal lineage as they could and admit their inability to track back to a couple.

Science is sometimes approximation. They assume that their genetic Eve and genetic Adam had parents – as opposed to having appeared on earth with some kind of magic, like converted from a toad. The geneticists recognize that mutations (changes in gene structure) were involved. There were mutations that moved creatures to what we now call human, and there were mutations that continued among humans that would change eye and skin color and other minor characteristics.

Mitochondrial Eve is estimated to have come into being perhaps as long ago as 200,000 years. And according to the journal Nature, science's Adam "did not live too far apart in time" from Eve. And these two early humans have been placed by paleo-anthropologists as living in East Africa.

Much older than our Mitochondrial Eve and Adam is the primate discovered in Ethiopia called Lucy (Australopithecus), known to us by her bone remains — palentology. Potassium-argon radiometric dating puts her as having lived 3.2 million years ago. Scientists calculate that chimpanzees and primates like Lucy started to diverge around 7 million years ago in Africa.

Paleo-anthropologists theorize that humans first appeared at one point in time and place – a theory called monogenism. A rival theory, polygenism, claims that there were multiple first appearances among humans, that humans of different races are descended from different first ancestors. Monogenism dominates within the scientific community.

Appearance of the human species has been described as coming with climate change, periods of cooling and drying, with dense forests thinning out producing woodlands and grasslands. Across a span of thousands of years, the primates that became human climbed down from trees and explored beyond the edge of dense forest.

Lucy was an adult and only 3'7" tall. She differed from chimpanzees in various ways. Her hips functioned much as human hips do, providing balance to the body as its strides standing on only one leg at a time. The humans who followed Lucy had shoulders that differed from the shoulders of chimpanzees, improving their ability to throw things, including spears. Humans were able to carry spears and other weapons or tools around as they walked on two legs rather than using all-four (or knuckle walking). Humans could still climb trees, but the structure of their ankles made this more difficult.

Humans ran after game, and running produced body heat. The development of sweat glands provided cooling. Our species lost what it no longer needed to survive. It lost its fur. It invented other means of keeping warm when that was desired. And there was "sexual selection." Females developed bulging mammaries. Individual tastes may have helped humans evolve from furry creatures. Humans had as many hairs as chimpanzees, but much of their hair was diminished to an almost invisible fuzz. And hair on the head of a woman may have had the same kind attraction that tail feathers had on a male peacock.

Genetic change within our species would endure and impact its existence. Each birth was not a creation of life but the passing on of life, but often with slight deviation. Some births would be malformations that could not participate in procreation. Other changes included the personalities of sons and daughters deviating from their parents, for better or worse, and the really bad ones would be driven out from the group. There were changes that allowed some to live a little longer than their parents, and gene mutations that produced a longer life might become more prevalant in a society.

Humans became able hunters, and they followed the animals they hunted in addition to gathering edible plants where they could. It is assumed that they moved about in small extended family groupings – as seen in hunter-gatherer societies still around in modern times. Their group was small enough that they knew each other well. Like other primates, healthy births produced people who socially capable, and they survived through team work and sharing.

In small groups, humans moved out of East Africa. They moved into nearby Arabia, where tools have been found that dated back 125,000 years. People moved into what today is China, where human teeth had been discovered that date back 80,000 years. Migrants to be known as aborigines are believed to have reached Australia at least by 65,000 years ago. (According to ABC News on July 2017, it was 18,000 years earlier than archaeologists had previously thought). A migration into Europe has been described as occurring 45,000 years ago. Meanwhile genetic changes within our species contributed to an appearance of different racial characteristics.

When the last Ice Age was reaching its peak around 25,000 years ago, a movement of people was underway from Asia to the North American continent. People were surviving on land between Siberia and what today is Alaska as a result of the low sea levels that accompanied the Ice Age. In the thousands of years that followed, people moved deeper into the North American continent. Stone spearheads and human DNA found in Oregon caves indicate "that at least two cultures with distinct technologies shared the continent more than 13,000 years ago." (New York Times, July 12, 2012.)


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Copyright © 2016 by Frank E. Smitha. All rights reserved.