Human Origins
Today, only one human species , Homo sapiens, exists, but over the Course of human prehistory as many as 15 varieties of early human walked the Earth. Though the number of species and their relationships to one another are not settled, it seems clear that the earliest hominids-aterm that describes all humans who ever lived-took their first steps in Africa.
they were( and we still are) primates, descended from a group of apes that also gave rise to gorrillas and chimpanzees. around 4 million years ago, something in the environment led the first hominds to leave the trees and walk upright, marking the official transition to human status. these early hominids are often grouped under the name Australopiths (from the term ''southernape") and include the genera Ardipithecus, Australopithecus, and paranthropus. about 3.5 to 5 feet tall, they had apelike face, with sloping foreheads and prominent Jaws, but their canine teeth were small compared with an ape's and their hands featured long, flexible thumbs. the most famous fossil member of these early humans is the Australopithecus afarensis known fondly as ''lucy,'' whose partial skeleton was discovered in 1974. Her species. which lived in eastern Africa between 3 and 4million years ago, is one leading candidate for being a direct ancestor of Homo sapiens.
Australopiths died out about 1.2 million years ago. By that time, their descendants, a new kind of homind, were already roaming Africa; the genus Homo, which came into exstence roughly 2.3 to 2.5 million years ago, was marked by a distinct increase in brain size. By 1.9 million years ago, these humans had tall skeletons like those of today's Homo sapiens, aithough their skulls still featured sloping foreheads, prominent brows, and heavy jaws.
These late species of Homo also demonstrated another similarity to modern humans; the desire to explore new lands. starting around 1.8 million years ago, the first great wave of human migration occurred when adventurous members of Homo erectus trekked out of Africa and into europe and Asia. However. these hominids eventually died out and were not the direct ancestors of today's humans. that honor falls to the first members of our own genus, Homo sapiens, who apeared in east Africa about 200,000 years ago.
- Mitochondrial Eve and Y Chromosome Adam
The study of human DNA has increased our knowledge of human origins and migration. Although virtually all of our DNA is recombined with every generation, two parts of the genome remain mostly unshuffled. The Y chromosome is passed down virtually unchanged from father to son. DNA in the cell's mitochondria, on the other hand, is passed down only from mothers to children.very rarely, but at a steady rate over time, a harmless mutation will occur in the DNA.this genetic marker will be carried through subsequent generations. geneticists have traced the markers to the original pair of Homo sapiens ancestors, ''mitochondrial Eve'' and ''Y chromosome Adam,'' two Africans who lived about 600,000 and 150,000 years ago, respectively.
- Mary Leakey / Anthropologist
The remarkable leakey family has dominated the field of anthropology since the mid 20th century .louis leakey (1903-1972). born in Africa of english missionaries, was an early proponent of an African orgin for modern humans. He and his wife, mary (1913-1996). made the 1948 discovery of the skull of an apelike creature, proconsul africanus,which gave evidence of a common ancestor of apes and humans. In 1959 Mary (left, in 1976) made an even more important discovery- paranthropus boisei in Africa's olduvai Gorge. In 1976 she found trail of human footprints, 3.6 million years old, in tanzania. son Richard (b. 1944). an anthropologist and kenyan politician, found the complete skeleton of a Homo erectus youth in 1985. and his wife, zoologist meave leakey (b. 1942). discovered some of the earliest Australopith skeletons ever found.
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