Human Evolution

views updated

Human Evolution

Human evolution is the process by which the modern species of humans was formed and developed. Although the major stages of human evolution are known, there are large gaps in our knowledge. It is now widely accepted that apes and humans evolved from the same ancestor. Many scientists believe that the earliest modern humans evolved first in Africa and then spread throughout the world.

Today's human beings, or Homo sapiens sapiens, belong to the hominid family tree. Hominid means "human types," and describes early creatures that split off from the apes and took to walking upright, or on their hind legs. In the overall history of life on Earth, the human species is a very recent product of evolution (the process by which living things change over generations). Since there are no human-like fossils older than 4,000,000 years, this makes us only one-thousandth the age of life on Earth. Today, most scientists agree that humans and apes evolved from the same ancestor. Where scientists cannot agree is how long ago this happened, where it happened, and how it happened. However, it has been demonstrated that the difference between the human genetic (heredity) code and that of a chimpanzee is only 0.7 percent.

It is not difficult to pinpoint what separates today's humans from the apes (gorillas, chimpanzees, orangutans, and gibbons). Some of these distinctions are more significant than mere physical difference. Humans have bigger brains and are intellectually superior. They have used this brain-power to develop tools, which have helped humans adapt to nearly any environment in which we choose to live. Humans are bipedal, meaning that they are able to walk on two feet, leaving their arms and hands free to make tools and do things. Finally, humans have developed language, a very sophisticated form of communication. But how did they separate from the apes and begin our own distinct evolutionary path toward what humans are today?

FOSSIL EVIDENCE

It is known humans evolved from the same ancestor as the apes. However, genetic evidence points to apes and humans going in different paths on the African continent between 10,000,000 and 6,000,000 years ago. Scientists have been able to assemble an impressive amount of fossil evidence that documents some of the branches on the hominid family tree.

Australopithecus afarensis. The oldest hominid scientists know about is called Australopithecus afarensis. It lived about 3,000,000 to 4,000,000 years ago and stood about 3.5 to 4 feet (1.07 to 1.22 meters) tall. It had a brain the size of a chimpanzee but it was clearly built for upright walking.

Homo habilis. Many scientists believe that the next known stage, Homo habilis who appeared about 2,000,000 years ago, came from Australopithecus. As the first hominid to be given the genus Homo, or "man," it was taller and used tools made of stone. Its name therefore means "capable man" or "handy man."

Homo erectus. By 1,500,000 years ago, it is known that a new, taller human species appeared and possessed a brain that was about half the size of humans today. Called Homo erectus, or "upright man," it was the first hominid to use fire and hand axes and to substantially move about. In fact, it is thought that this species left Africa and gradually migrated into Asia and parts of Europe.

Homo sapiens. Homo sapiens, or "wise man," are thought to have appeared about 400,000 years ago. With a still-larger brain and more human features like smaller teeth and a clearly defined chin, it used more sophisticated tools and buried its dead.

Neanderthals and Cro-Magnons. One form of Homo sapiens, known as Neanderthals, eventually died out. Some argue that Neanderthals evolved into the Cro-Magnons. Others say that the Cro-Magnons were a separate species and simply out-competed or killed the Neanderthals. In 1997, genetic studies of a Neanderthal bone revealed no evidence of a genetic connection to modern man, suggesting that they may have been a separate and distinct species that went extinct. Nonetheless, it was the Cro-Magnons who survived and continued to reproduce. They were humans who mostly looked like us, although with possibly broader faces, and they had moved into Europe. Their population increased rapidly and they began to develop a culture of some kind.

Homo sapiens sapiens. Finally, the emergence of fully modern humans, now called Homo sapiens sapiens, or doubly "wise" man, came about some 40,000 to 15,000 years ago. This creature was physically identical to today's humans and had real language. Humans moved from being strictly hunters and gatherers to domesticating animals and plants and creating fine artwork. Soon, their settlements had turned into real cities, and a civilization was created based on agriculture (farming). Recent studies of fossil fragments found in a cave in Israel suggest that modern humans (Homo sapiens sapiens) may have existed as far back as 92,000 years ago. Despite more information regularly coming to light, the human race still has not solved the complete mystery of human evolution at the beginning of the twenty-first century.