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Question: Why are people on this earth?
This is a very complex and timely question, considering that the 200th birthday of biology\\\'s "reluctant revolutionary," Charles Darwin was just a few weeks ago, Thursday, February 12. While Darwin was known to be a quiet man "Darwin Day," the name given to last weeks celebrations, was anything but. The official celebration website (darwinday.org) listed over 280 events in 31 nations.
So back to our question, one in which there is considerable disagreement about. Some scientists work with fossils, that is, mostly teeth and bones of animals and humans who lived in the past. If they work with human fossils and those of our closest relatives, the primates (including monkeys and apes), they call themselves paleoanthropologists. It is important to point out that humans are primates, as well, since we belong to this group of unusual animals. By looking at bones and teeth we can determine what kind of creatures lived in the past by reconstructing them from their bones and teeth. Therefore, we have a pretty good idea of what our distant ancestors looked like and we can trace their evolutionary pathways from millions of years ago up to the present. This doesn't mean that all of the paleoanthropologists agree on which pathways and which ancestors led to modern humans.
There is considerable disagreement since the pathways from the distant past are very complex, indeed, and some of them have led to extinctions (dead ends where species die off). Other pathways have led to more advanced creatures and then finally to modern humans. The reason why some evolutionary pathways lead to successful groups of animals that persist through time and others do not is not generally known. Some scientists suggest that there are people on the earth because we are smart and very capable of feeding ourselves and having offspring. Others say that it is just luck and that we might not be here if we had taken slightly different evolutionary pathways.
At present, we can trace our human-like ancestors back to about 6 million years ago in Africa, but these would not be recognized as humans as we know them. They might look more like apes (the Bonobo Chimpanzee is a good example) who walked upright on their hind legs, rather than walking on all fours as do most apes. Their brains were much smaller than ours, but they were pretty smart, as are most of our closest living relatives, the gorilla and the chimp. Over the next several million years these human ancestors evolved into a more advanced form called Australopithecus. Australopithecus walked on two legs, and had a slightly larger brain and a flatter face than the earlier ancestors of 6 million years ago. By about 2 million years ago a new form of ancestor evolved who finally looked somewhat human. These ancestors had distinctly larger brains than earlier ones and they made stone tools, both traits that set them apart from all other animals.
All of these evolutionary changes occurred in Africa up to this point. After this time, our ancestors moved into Europe and Asia and continued to evolve. About 200,000 years ago humans who had remained in Africa had evolved to look pretty much like you or I, and then moved out of Africa again to populate much of the world. They first moved into Asia and Europe, then much later moved from Asia to Australia, then North and South America, and then to the Pacific islands. People have moved all over the planet since that time, so we are continually becoming more and more mixed as members of the same species. Throughout our evolutionary history, there have been populations that became extinct (died out) and others that were our ancestors. The famous Neanderthal population from thousands of years ago in Europe is now believed to be one of those groups to become extinct. Our best evidence for this is through studies of ancient Neanderthal DNA that show very little relationship to modern humans.
This is really just a sketch of our evolution, and represents how rather than why we are on the earth. But this evidence is pretty well established and based on the studies of paleoanthropologists and archaeologists who have worked very hard over the past 150 years.
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