Some years ago I published a series of articles about evolution in my local newspaper. It generated some interest and a spate of letters to the editor, and my publisher liked it. There was even a creationist who challenged me to a debate over it. I decided to reproduce it here. This is part three, which I called Walk This Way. See also Part One and Part Two.
The first primates show up in the fossil record about 50-55 million years ago. They are part of the resulting explosion of new species that evolved to fill environmental niches vacated by the non-avian dinosaurs, after they went extinct sixty-five million years ago. Many of the new species are mammals, and we see a mammal-dominated landscape right now. Of the mammals, it is the primates which interest us the most, as they are our ancestors. Primates spread out and evolved into many different species, including lemurs, monkeys and apes. They can be found in most parts of the world, but it was in Africa where the line led to humans.
Between seven and eight million years ago a primate living in Africa split into two species. Such splits normally result when two populations of one species get separated somehow. Something like that happened to the common ancestor of chimpanzees and humans. A fossil from that period shows definite signs of an upright, two-legged gait, but the oldest hominin fossil with extensive bipedal adaptations is Ardipithecus ramidus. That was the beginning of the hominin, or human-like primate. Since then it evolved and radiated out into many different hominin species, most of which have gone extinct.
The first evidence of stone tools shows up at least 2.6 million years ago, with some evidence that pre-homo hominins were using them as early as 3.3 million years ago. Undoubtedly they were using tools made of other materials like wood and grass, but only stone can survive long enough for us to find.
Homo erectus is thought to have tamed fire by about 1.8 million years ago. Others put the use of hearths beginning later, at about 800,000 and even only 300,000 years ago. Much of the discussion revolves around whether we were simply burning grasslands to improve hunting, or actually sitting around a hearth cooking food on a regular basis. Those favoring the earlier date cite the shrinking jaw and growing brain of H. erectus as evidence that they were cooking their food. The pinnacle of upright hominids seemed to have been reached, but their brains were only about half the size of ours. Larger than the brains of similar-sized animals, but still too small by our standards.
Increasing brain size was the next big step. By the time we reach the age of Neanderthals, about four hundred thousand years ago, and modern humans at about half that, our brains were as big as they are now.
Since then it’s been a matter of social and technological evolution. The first jewelry shows up about 75-100 thousand years ago. The first garments appear to have been manufactured about 100 thousand years earlier, based on the evolution of body lice. The tool set became extremely sophisticated.
Neanderthals died out about thirty thousand years ago, leaving only a single hominid species on Earth for the first time in millions of years. Our cultural evolution continued to accelerate, as evidenced by sophisticated cave paintings, bringing us to the present state of high civilization.
Let’s hope we’re not due for another mass extinction.