Monday, June 19, 2017

In Search of our Ancient Ancestors – New Evidence

View from Jebel Irhoud
Photo: Flickr
A re-evaluation of early human remains and artefacts from Morocco has pushed back the advent of Homo sapiens by 100,000 years. Archaeologists and palaeontologists believe that the oldest of the fossils comes from 300,000 to 350,000 years ago. Skulls, teeth, and long bones of at least five Homo sapiens, along with stone tools and animal bones, have been found at Jebel Irhoud, Morocco since 2004. Prior to this discovery, the oldest accepted dating for Homo sapiens remains were said to be from the site of Omo Kibish in Ethiopia, dated to 195,000 years ago and Herto, also in Ethiopia, from 160,000 years ago .
Although stone tools were found all over Africa by 300,000 years ago, human fossils were thought to be no older than 195,000 years old. One possibility was that the stone tools had been made by some hominid (any member of the group consisting of all modern and extinct humans and great apes - including gorillas, chimpanzees, and orangutans - and all their immediate ancestors) other than Homo sapiens. Jebel Irhoud is considered to be the oldest and richest African Middle Stone Age hominin site that documents early stages of the Homo sapiens.
Composite Reconstruction of Skull from
        Jebel Irhound - Photograph: Flickr
Today, modern humans or Homo sapiens, inhabit the whole earth. Looking back over the last half a million years, the picture was much more diverse, with three distinct lineages appearing: Homo erectus in Asia; and Homo heidelbergensis giving rise to Homo neanderthals in Europe and Homo sapiens in Africa. Excavations in Ibex, Vanguard, and Gorham’s Caves in Gibraltar have revealed evidence of Neanderthal occupation dating to possibly as late as 28,000 years ago.
This dispersal out of Africa is believed to have started from Northeast Africa. Modern humans later spread worldwide, replacing earlier ancestors either through competition or interbreeding. The first fossil evidence for any modern humans outside Africa comes from the Middle East, from the archaeological sites of Skhul and Qafzeh in Israel, dating to around 120,000 years ago.
The skeleton of an adolescent early Homo sapiens was found at the Qafzeh Cave site near Nazareth, buried in a pit dug into bedrock. The skeleton was lying on its back with both arms flexed upwards and a set of deer antlers laid across the chest. The burial dates to around 100,000-80,000 years ago and may represent a form of ritual possibly indicating a belief in an afterlife. However, this early expansion of modern humans was not maintained.
The ancestors of modern humans interbred with Neanderthals and another extinct line of humans known as the Denisovans. Modern humans, Neanderthals and Denisovans shared a common ancestor who lived roughly 600,000 years ago. The interbreeding may have given modern humans genes that bolstered immunity to pathogens. The first clues to ancient interbreeding surfaced in 2010, when scientists discovered that some modern humans — mostly Europeans — carried DNA that matched material recovered from Neanderthal fossils.
There are, however, conflicting models of human expansion. The so called Regional Continuity theory suggests that Homo sapiens arose from earlier, archaic populations in many places throughout the Old World. Over time, archaic populations in Africa, Europe, and Asia developed into Homo sapiens. In this view, the lineages represented by Homo ergaster in Africa, Home erectus in Asia, and Homo neanderthals in Europe have all survived, and modern humans are their descendants.
The recent African Origin model proposes a more localised point of origin for our species. The earliest Homo sapiens fossils are found in Africa, and genetic research on living humans points to the recent evolution of our species in Africa. Genetic evidence also supports a model of expansion, with our species emerging out of Africa and largely replacing earlier, archaic populations.
Sometime after 80,000 years ago, a population expansion and migration began, which would lay the foundations of modern humans colonising the globe. Although the archaeological evidence is not conclusive, the genetic trail leads out of Africa, through the Middle East, into southern and South Asia, and all the way to Australia.
The presence of early Homo Sapiens in north Africa complicates our understanding of humanity arising in the east of the continent. Researchers used to think that there was a cradle of humankind in East Africa about 200,000 years ago, and all modern humans descend from that population. The new finds indicate that Homo sapiens is much older and had already spread across all of Africa by 300,000 years ago.
It’s possible that in the Middle Stone Age early humans spread all over Africa, aided by their new stone technology of smaller, lighter tools such as spear tips rather than larger stone hand axes. At the time, the Sahara was a lush, green savannah and not the impassable desert of today. Alternatively, humans may have already spread throughout the continent and developed Middle Stone Age tools independently.
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