The human evolution and its developments has always fascinated me. Its interesting to know and learn about the path of evolution which human species under went over the 5 million years from where the evolution believed to be taken place and slowly in to present day humans.The record of human evolution extends back from more than 6 million years from Africa, to the point when our lineage split from that of chimpanzees, our closest living relatives, to about 5 million years. Although Homo sapiens is the only surviving human species, we are part of a large human family tree. The fossil record has so far revealed evidence for more than 20 species of ancient human relatives hominines,The modern humans as we call it as Homo sapiens began their journey from African continent only 60,000 years ago.The rapid expansion of humankind to North America and Oceania took place at the peak of the Ice Age when temperate regions of present day were extremely inhospitable. They have almost reached all continents by 50,000 years. At the same time the other species of humans and our hominid cousins ie Neanderthals and Denisovans also existed with Homo sapiens or modern man. All three different humans species lived simultaneously in different parts of earth until 25000 years ago.
Modern humans spread rapidly from Africa into the frost-free zones of Europe and Asia they were not alone. The Neanderthals and Denisovans had already made the same journey and left Africa about 300,000 years ago and Neanderthals settled in Europe and parts of western Asia. The Denisovans are a much more recent addition to the human family tree. In 2008, paleo anthropologists digging in a cave in southern Siberia unearthed a 40,000-year-old adult tooth and an exquisitely preserved fossilized pinkie bone that had belonged to a young girl who was between five and seven years old when she died.
Recently, scientists successfully
extracted nuclear DNA from the pinkie bone and conducted comparison studies
with the genomes of modern humans and Neanderthals. Studies show the girl was
closely related to Neanderthals, yet distinct enough to merit classification as
a new species of archaic humans, which scientists named “Denisovan” after the
cave where the pinkie bone was found. The Denisovan genome also suggests the
young girl had brown hair, eyes, and skin.
Surprisingly, the scientists found genetic overlap between the Denisovan
genome and that of some present-day east Asians, and, in particular, a group of
Pacific Islanders living in Papua New Guinea, known as the Melanesians. It
appears the Denisovans contributed between 3 to 5 percent of their genetic
material to the genomes of Melanesians. Scientists think that the most likely
explanation is that Denisovans living in eastern Eurasia interbred with the
modern human ancestors of Melanesians. When those humans crossed the ocean to
reach Papua New Guinea around 45,000 years ago, they brought their Denisovan
DNA over with them.
If this genetic mixing did occur, the fact that Denisovans were
discovered in Siberia but contributed to the genomes of modern humans living in
Southeast Asia suggests the species ranged widely across Asia, although their
low genetic diversity also indicates their numbers were never very high.
According to one theory, Neanderthals,
Denisovans, and modern humans are all descended from the ancient human Homo
heidelbergensis. Between 300,000 to 400,000 years ago, an ancestral group
of H. heidelbergensis left Africa and then split shortly
after. One branch ventured northwestward into West Asia and Europe and became
the Neanderthals. The other branch moved east, becoming Denisovans. By 130,000
years ago, H. heidelbergensis in Africa had become Homo
sapiens—our ancestors—who did not begin their own exodus from Africa until
about 60,000 years ago.
By
comparing the genomes of apes, Denisovans, Neanderthals, and modern humans,
scientists hope to identify DNA segments unique to the different groups. Early
results already suggest modern humans underwent genetic changes involved with
brain function and nervous system development, including ones involved in
language development, after splitting from Neanderthals and Denisovans..
