The first fossils of early modern humans to be identified were found in at the 27 , , year old Cro-Magnon rock shelter site near the village of Les Eyzies in southwestern France. They were subsequently named the Cro-Magnon people. The y were very similar in appearance to modern Europeans.
Males were 5 feet 4 inches to 6 feet tall 1. That was inches cm. Their skeletons and musculature generally were less massive than the Neandertals. The Cro-Magnon had broad, small faces with pointed chins and high foreheads. Their cranial capacities were up to cm 3 , which is relatively large even for people today.
Origins of Modern Humans. Current data suggest that modern humans evolved from archaic humans primarily in East Africa. A , year old fossil from the Omo 1 site in Ethiopia shows the beginnings of the skull changes that we associate with modern people, including a rounded skull case and possibly a projecting chin. A , year old skull from the Herto site in the Middle Awash area of Ethiopia also seems to be at the early stages of this transition. It had the rounded skull case but retained the large brow ridges of archaic humans. Somewhat more advanced transitional forms have been found at Laetoli in Tanzania dating to about , years ago.
By , years ago, early modern humans had expanded their range to South Africa and into Southwest Asia Israel shortly after , years ago.
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There is no reliable evidence of modern humans elsewhere in the Old World until 60,, years ago, during a short temperate period in the midst of the last ice age. Liujiang China ,,? Z hirendong China ,? Dating of the earliest modern human fossils in Asia is less secure, but it is likely that they were present there by at least 60, years ago and possibly , years ago. It would seem from these dates that the location of initial modern Homo sapiens evolution and the direction of their dispersion from that area is obvious.
That is not the case. Since the early 's, there have been two leading contradictory models that attempt to explain modern human evolution--the replacement model and the regional continuity model.
The replacement model of Christopher Stringer and Peter Andrews proposes that modern humans evolved from archaic humans , 5 0, years ago only in Africa and then some of them migrated into the rest of the Old World replacing all of the Neandertals and other late archaic humans beginning around 60,, years ago or somewhat earlier. If this interpretation of the fossil record is correct, all people today share a relatively modern African ancestry. All other lines of humans that had descended from Homo erectus presumably became extinct. From this view, the regional anatomical differences that we now see among humans are recent developments--evolving mostly in the last 40, years.
This hypothesis is also referred to as the " out of Africa ", " Noah's ark ", and "African replacement" model. The regional continuity model or multiregional evolution model advocated by Milford Wolpoff proposes that modern humans evolved more or less simultaneously in all major regions of the Old World from local archaic humans.
For example, modern Chinese are seen as having evolved from Chinese archaic humans and ultimately from Chinese Homo erectus. This would mean that the Chinese and some other peoples in the Old World have great antiquity in place. Supporters of this model believe that the ultimate common ancestor of all modern people was an early Homo erectus in Africa who lived at least 1.
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- Recent African origin of modern humans.
- Ancient human species may have lived alongside our Homo sapien ancestors;
It is further suggested that since then there was sufficient gene flow between Europe, Africa, and Asia to prevent long-term reproductive isolation and the subsequent evolution of distinct regional species. It is argued that intermittent contact between people of these distant areas would have kept the human line a single species at any one time.
However, regional varieties, or subspecies, of humans are expected to have existed. Replacement Model Arguments. There are two sources of evidence supporting the replacement model--the fossil record and DNA. So far, the earliest finds of modern Homo sapiens skeletons come from Africa.
They date to nearly , years ago on that continent.
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They appear in Southwest Asia around , years ago and elsewhere in the Old World by 60, , years ago. Unless modern human remains dating to , years ago or earlier are found in Europe or East Asia, it would seem that the replacement model better explains the fossil data for those regions. However, the DNA data supporting a replacement are more problematical. Beginning in the 's, Rebecca Cann, at the University of California , argued that the geographic region in which modern people have lived the longest should have the greatest amount of genetic diversity today.
Through comparisons of mitochondrial DNA sequences from living people throughout the world, she concluded that Africa has the greatest genetic diversity and , therefore , must be the homeland of all modern humans. Assuming a specific , constant rate of mutation, she further concluded that the common ancestor of modern people was a woman living about , years ago in Africa.
This supposed predecessor was dubbed "mitochondrial Eve". More recent genetic research at the University of Chicago and Yale University lends support to the replacement model.
It has shown that variations in the DNA of the Y chromosome and chromosome 12 also have the greatest diversity among Africans today. John Relethford and other critics of the replacement model ha ve pointed out that Africa could have had the greatest diversity in DNA simply because there were more people living there during the last several hundred thousand years.
This would leave open the possibility that Africa was not necessarily the only homeland of modern humans. Critics of th e genetic argument for the replacement model also point out that the rate of mutation used for the "molecular clock" is not necessarily constant , which makes the , year date for "mitochondrial Eve" unreliable. In addition, some kinds of DNA molecules are known to be more subject to mutation than others, resulting in faster mutation rates. This seems to be the case with the Y chromosome in human males.
Further criticism of the genetic argument for the replacement model has come from geneticists at Oxford University. They found that the human betaglobin gene is widely distributed in Asia but not in Africa. Since this gene is thought to have originated more than , years ago, it undercuts the claim that an African population of modern Homo sapiens replaced East Asian archaic humans less than 6 0, years ago.
Regional Continuity Model Arguments. Fossil evidence also is used to support the regional continuity model. Its advocates claim that there has been a continuity of some anatomical traits from archaic humans to modern humans in Europe and Asia. In other words, the Asian and European physical characteristics have antiquity in these regions going back over , years. They point to the fact that many Europeans have relatively heavy brow ridges and a high angle of their noses reminiscent of Neandertals.
Similarly, it is claimed that some Chinese facial characteristics can be seen in an Asian archaic human fossil from Jinniushan dating to , years ago. Modern humans' stone tools and weapons usually featured elongated, standardized, finely crafted blades. Both species hunted and killed the same large mammals, including deer, horses, bison and wild cattle. But moderns' sophisticated weaponry, such as throwing spears with a variety of carefully wrought stone, bone and antler tips, made them more successful.
And the tools may have kept them relatively safe; fossil evidence shows Neanderthals suffered grievous injuries, such as gorings and bone breaks, probably from hunting at close quarters with short, stone-tipped pikes and stabbing spears. Both species had rituals—Neanderthals buried their dead—and both made ornaments and jewelry.
But the moderns produced their artifacts with a frequency and expertise that Neanderthals never matched. And Neanderthals, as far as we know, had nothing like the etching at Blombos Cave, let alone the bone carvings, ivory flutes and, ultimately, the mesmerizing cave paintings and rock art that modern humans left as snapshots of their world. When the study of human origins intensified in the 20th century, two main theories emerged to explain the archaeological and fossil record: one, known as the multi-regional hypothesis, suggested that a species of human ancestor dispersed throughout the globe, and modern humans evolved from this predecessor in several different locations.
The other, out-of-Africa theory, held that modern humans evolved in Africa for many thousands of years before they spread throughout the rest of the world. In the s, new tools completely changed the kinds of questions that scientists could answer about the past. By analyzing DNA in living human populations, geneticists could trace lineages backward in time.
These analyses have provided key support for the out-of-Africa theory. Homo sapiens , this new evidence has repeatedly shown, evolved in Africa, probably around , years ago. The first DNA studies of human evolution didn't use the DNA in a cell's nucleus—chromosomes inherited from both father and mother—but a shorter strand of DNA contained in the mitochondria, which are energy-producing structures inside most cells. Mitochondrial DNA is inherited only from the mother. Conveniently for scientists, mitochondrial DNA has a relatively high mutation rate, and mutations are carried along in subsequent generations.
By comparing mutations in mitochondrial DNA among today's populations, and making assumptions about how frequently they occurred, scientists can walk the genetic code backward through generations, combining lineages in ever larger, earlier branches until they reach the evolutionary trunk. At that point in human history, which scientists have calculated to be about , years ago, a woman existed whose mitochondrial DNA was the source of the mitochondrial DNA in every person alive today. That is, all of us are her descendants. Scientists call her "Eve.
But she did live at a time when the modern human population was small—about 10, people, according to one estimate. She is the only woman from that time to have an unbroken lineage of daughters, though she is neither our only ancestor nor our oldest ancestor. She is, instead, simply our "most recent common ancestor," at least when it comes to mitochondria.
Homo sapiens - Wikipedia
Subsequent, more sophisticated analyses using DNA from the nucleus of cells have confirmed these findings, most recently in a study this year comparing nuclear DNA from people from 51 parts of the world. This research, the most comprehensive to date, traced our common ancestor to Africa and clarified the ancestries of several populations in Europe and the Middle East.
While DNA studies have revolutionized the field of paleoanthropology, the story "is not as straightforward as people think," says University of Pennsylvania geneticist Sarah A. If the rates of mutation, which are largely inferred, are not accurate, the migration timetable could be off by thousands of years. To piece together humankind's great migration, scientists blend DNA analysis with archaeological and fossil evidence to try to create a coherent whole—no easy task. A disproportionate number of artifacts and fossils are from Europe—where researchers have been finding sites for well over years—but there are huge gaps elsewhere.
As the gaps are filled, the story is likely to change, but in broad outline, today's scientists believe that from their beginnings in Africa, the modern humans went first to Asia between 80, and 60, years ago. By 45, years ago, or possibly earlier, they had settled Indonesia, Papua New Guinea and Australia. The moderns entered Europe around 40, years ago, probably via two routes: from Turkey along the Danube corridor into eastern Europe, and along the Mediterranean coast.
By 35, years ago, they were firmly established in most of the Old World. The Neanderthals, forced into mountain strongholds in Croatia, the Iberian Peninsula, the Crimea and elsewhere, would become extinct 25, years ago. Finally, around 15, years ago, humans crossed from Asia to North America and from there to South America.
Africa is relatively rich in the fossils of human ancestors who lived millions of years ago see timeline, opposite. Lush, tropical lake country at the dawn of human evolution provided one congenial living habitat for such hominids as Australopithecus afarensis. Many such places are dry today, which makes for a congenial exploration habitat for paleontologists. Wind erosion exposes old bones that were covered in muck millions of years ago.