Dec 8, 2012

How long have humans been on Earth?

We’ve evolved through a very lengthy process of evolution -- during certain phases we may have looked like apes. Scientific evidence shows that the physical and behavioral traits shared by all people evolved over a period of at least 6 million years.

One of the earliest defining human traits, bipedalism—walking on two legs, as the primary form of locomotion—evolved more than 4 million years ago. Other important human characteristics—such as a large and complex brain, the ability to make and use tools, and the capacity for language—developed more recently. Many advanced traits—including complex symbolic expression, such as art, and elaborate cultural diversity—emerged mainly during the last 100,000 years. It is estimated that our ancestors lived between 8 million and 5 million years ago.

Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens, has a very close relationship to another group of primate species, the apes. The earliest humans evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 million and 2 million years ago come entirely from Africa.

Most scientists distinguish among 12 to 19 different species of early humans. Scientists do not all agree, however, about how the species are related or which ones simply died out. Many early human species—probably the majority of them—left no descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution or extinction of each species.

Early humans first migrated out of Africa into Asia probably between 2 million and 1.7 million years ago. They entered Europe somewhat later, generally within the last 1 million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the last 60,000 years, and to the Americas within the last 35,000 years. The beginnings of agriculture and the rise of the first civilizations occurred within the last 10,000 years.

Scientists have discovered the bones and artifacts of early humans in many parts of Africa and Eurasia. The earliest humans, known as australopithecines, lived only in Africa. The modern human genus, Homo, also evolved in Africa, but several middle and late Homo species migrated to Europe and Asia. Early forms of Homo sapiens, or modern humans, lived in Africa and Asia. Only fully modern humans populated the rest of the globe.  (Adapted from Encarta Encyclopedia)