The long travel of Home Sapiens
Antecessor
A map of early human migrations
Homo sapiens –
Neanderthals – 2
Early Hominids – 3
Migration rout of the Homo Sapiens
Haplogroup E1b1b (formerly E3b) represents the last direct major migration from Africa into Europe. It is believed to have first appeared in the Horn of Africa (some also suggest southern Africa) approximately 26,000 years ago and dispersed to the Middle East during the Upper Paleolithic and Mesolithic periods.
On the European continent it has the highest concentration in north-west Greece, Albania and Kosovo, then fading around the Balkans, the rest of Greece and Western Turkey. Outside Europe, it is also found in most of the Middle East, northern and eastern Africa, especially in Morocco, Libya, Egypt Yemen, Somalia, Ethiopia and South Africa.
Mitochondrial Eve & Y-chromosomal Adam
The matrilinear most recent common ancestor shared by all living human beings, dubbed Mitochondrial Eve, probably lived roughly 120-150 millennia ago, the time of Homo sapiens idaltu, probably in East Africa, when Homo sapiens sapiens (anatomically modern humans) were developing as a population distinct from other human sub-species.
Mitochondrial Eve lived later than Homo heidelbergensis and the emergence of Homo neanderthalensis, but earlier than the out of Africa migration. The dating for ‘Eve’ was a blow to the multiregional hypothesis, and a boost to the hypothesis that modern humans originated relatively recently in Africa and spread from there, replacing more “archaic” human populations such as Neanderthals. As a result, the latter hypothesis became dominant.
The broad study of African genetic diversity headed by Dr. Sarah Tishkoff found the San people to express the greatest genetic diversity among the 113 distinct populations sampled, making them one of 14 “ancestral population clusters.” The research also located the origin of modern human migration in south-western Africa, near the coastal border of Namibia and Angola.
Around 100,000-80,000 years ago, three main lines of Homo sapiens diverged. Bearers of mitochondrial haplogroup L0 (mtDNA) / A (Y-DNA) colonized Southern Africa (the ancestors of the Khoisan (Capoid) peoples), bearers of haplogroup L1 (mtDNA) / B (Y-DNA) settled Central and West Africa (the ancestors of western pygmies), and bearers of haplogroups L2, L3, and others mtDNA remained in East Africa (the ancestors of Niger–Congo- and Nilo-Saharan-speaking peoples).
Mitochondrial Eve is the female counterpart of Y-chromosomal Adam, the patrilineal most recent common ancestor, although they lived thousands of years apart. Like mitochondrial “Eve”, Y-chromosomal “Adam” probably lived in Africa; however, this “Eve” lived much earlier than this “Adam” – perhaps even some 50,000 to 80,000 years earlier though recent studies have suggested that the difference may be less than previously thought. Recent studies report that Y-chromosomal Adam lived as early as around 142,000 years ago.
Y-chromosomal Adam had at least two sons and two of his sons have unbroken lineages that have survived to the present day. Initial sequencing of the human Y chromosome suggested that two most basal Y-chromosome lineages were Haplogroup A and Haplogroup BT. Haplogroup A is found at low frequencies in parts of Africa, but is common among certain hunter-gatherer groups. Haplogroup BT lineages represent the majority of African Y-chromosome lineages and virtually all non-African lineages.
Y-chromosomal Adam was represented as the root of these two lineages. Haplogroup A and Haplogroup BT represented the lineages of the two sons of Y-chromosomal Adam.
When deep rooting haplogroups are permanently lost from the world’s population, living human Y chromosomes converge on a more recent common ancestor. A Y-chromosome lineage is halted when a male dies without leaving any male offspring (although this individual may or may not have had daughters). Phenomena such as bottlenecks and genetic drift during human evolution would have caused the total extinction of several basal haplogroups. Because of these factors, the title “Y-chromosomal Adam” has changed hands numerous times.
Further sampling of Y chromosomes could uncover previously unknown divergent lineages. If this happens, Y-chromosome lineages would converge on an individual who lived further back in time. The discovery of additional deep rooting mutations in known lineages could lead to a rearrangement of the family tree.
Initial studies implicated East Africa and Southern Africa as the likely sources of human Y-chromosome diversity. This was because the basal lineages, Haplogroup A and Haplogroup B achieve their highest frequencies in these regions. But the most basal lineages have been detected in West, Northwest and Central Africa.
In a sample of 2204 African Y-chromosomes, 8 chromosomes belonged to either haplogroup A1b or A1a. Haplogroup A1a was identified in two Moroccan Berbers, one Fulbe and one Tuareg from Niger. Haplogroup A1b was identified in three Bakola pygmies from Southern Cameroon and one Algerian Berber. It is now suggested a Y-chromosomal Adam, living somewhere in Central-Northwest Africa, fits well with the data.
Early human migrations
Early human migrations began when Homo erectus first migrated out of Africa over the Levantine corridor and Horn of Africa to Eurasia about 1.8 million years ago. The expansion of H. erectus out of Africa was followed by that of Homo antecessor into Europe around 800,000 years ago, followed by Homo heidelbergensis around 600,000 years ago, where they probably evolved to become the Neanderthals. Modern humans, Homo sapiens, evolved in Africa up to 200,000 years ago and reached the Near East around 125,000 years ago.
Some scientists believe that only a few people left Africa in a single migration that went on to populate the rest of the world, based in the fact that only descents of L3 are found outside Africa. From that settlement, some others point to the possibility of several waves of expansion. Early travellers followed the southern coastline of Asia, crossed about 155 miles of sea, and colonized Australia by around 50,000 years ago. The Aborgines of Australia are the descendants of the first wave of migrations.
It has been estimated that from a population of 2,000 to 5,000 individuals in Africa, only a small group, possibly as few as 150 to 1,000 people, crossed the Red Sea. Of all the lineages present in Africa only the female descendants of one lineage, mtDNA haplogroup L3, are found outside Africa. Had there been several migrations one would expect descendants of more than one lineage to be found outside Africa.
L3’s female descendants, the M and N haplogroup lineages, are found in very low frequencies in Africa (although haplogroup M1 is very ancient and diversified in North and Northeast Africa) and appear to be recent arrivals. A possible explanation is that these mutations occurred in East Africa shortly before the exodus and by the founder effect became the dominant haplogroups after the exodus from Africa. Alternatively, the mutations may have arisen shortly after the exodus from Africa.
Other scientists have proposed a Multiple Dispersal Model, in which there were two migrations out of Africa, one across the Red Sea travelling along the coastal regions to India (the Coastal Route), which would be represented by Haplogroup M. Another group of migrants with Haplogroup N followed the Nile from East Africa, heading northwards and crossing into Asia through the Sinai. This group then branched in several directions, some moving into Europe and others heading east into Asia. This hypothesis attempts to explain why Haplogroup N is predominant in Europe and why Haplogroup M is absent in Europe.
Evidence of the coastal migration is hypothesized to have been destroyed by the rise in sea levels during the Holocene epoch. Alternatively, a small European founder population that initially expressed both Haplogroup M and N could have lost Haplogroup M through random genetic drift resulting from a bottleneck (i.e. a founder effect).
There is some evidence for the argument that modern humans left Africa at least 125,000 years before present (BP) using two different routes: the Nile Valley heading to the Middle East, at least into modern Israel (Qafzeh: 120,000–100,000 years BP); and a second one through the present-day Bab-el-Mandeb Strait on the Red Sea (at that time, with a much lower sea level and narrower extension), crossing it into the Arabian Peninsula, settling in places like the present-day United Arab Emirates (125,000 years BP) and Oman (106,000 years BP) and then possibly going into the Indian Subcontinent (Jwalapuram: 75,000 years BP).
Despite the fact that no human remains have yet been found in these three places, the apparent similarities between the stone tools found at Jebel Faya, the ones from Jwalapuram and some African ones suggest that their creators were all modern humans.
These findings might give some support to the claim that modern humans from Africa arrived at southern China about 100,000 years BP (Zhiren Cave, Zhirendong, Chongzuo City: 100,000 years BP; and the Liujiang hominid: controversially dated at 139,000–111,000 years BP).
Since these previous exits from Africa did not leave traces in the results of genetic analyses based on the Y chromosome and on MtDNA (which represent only a small part of the human genetic material), it seems that those modern humans did not survive or survived in small numbers and were assimilated by our major antecessors, responsible for a determinant posterior exit.
An explanation for their extinction (or small genetic imprint) may be the Toba catastrophe theory (74,000 years BP). However, some argue that its impact on human population was not dramatic.
According to the Recent African Origin theory a small group of the L3 bearers living in East Africa migrated north east, possibly searching for food or escaping adverse conditions, crossing the Red Sea about 70 millennia ago, and in the process going on to populate the rest of the world.
Based in the fact that only descents of L3 are found outside Africa, only a few people left Africa in a single migration to a settlement in the Arabian peninsula. From that settlement there seems to be several waves of expansion close in time.
From the Near East, these populations spread east to South Asia by 50,000 years ago, and on to Australia by 40,000 years ago, when for the first time H. sapiens reached territory never reached by H. erectus. H. sapiens reached Europe around 43,000 years ago, eventually replacing the Neanderthal population. East Asia was reached by 30,000 years ago.
The early travelers followed the southern coastline of Asia, crossed about 250 kilometers [155 miles] of sea (probably by simple boats or rafts, and colonized Australia by around 50,000 years ago. The Aborigines of Australia are the descendants of the first wave of migration out of Africa.
If these dates are correct, Australia was populated up to 10,000 years before Europe. This is possible because humans avoided the colder regions of the North favoring the warmer tropical regions to which they were adapted given their African homeland. Another piece of evidence favoring human occupation in Australia is that beginning about 46,000 years ago, all megafauna weighing more than 100 kg became extinct. Tim Flannery and others argue new settlers were likely to be responsible for this extinction. Many of the animals may have been accustomed to living without predators and become docile and vulnerable to attack (as occurred later in the Americas).
Around 50,000 years ago the world was entering the last ice age and water was trapped in the polar ice caps, so sea levels were much lower. Today at the Gate of Grief the Red Sea is about 12 miles (20 kilometres) wide but 50,000 years ago it was much narrower and sea levels were 70 metres lower. Though the straits were never completely closed, there may have been islands in between which could be reached by simple rafts. Shell middens 125,000 years old indicate that the diet of early humans in Eritrea included sea food obtained by beachcombing. This has been seen as evidence that humans may have crossed the Red Sea in search of food sources on new beaches
The date of migration to North America is disputed; it may have taken place around 30 millennia ago, or considerably later, around 14 millennia ago. Colonisation of the Pacific islands of Polynesia began around 1300 BC, and was completed by 900 AD. The ancestors of Polynesians left Taiwan around 5200 years ago.
Europe is thought to have been colonized by northwest bound migrants from Central Asia and the Middle East. When the first anatomically modern humans entered Europe, Neanderthals were already settled there. Debate exists whether modern human populations interbred with Neanderthal populations, most of the evidence suggesting that it happened to a small degree rather than complete absorption. Populations of modern man and Neanderthal overlapped in various regions such as in Iberian peninsula and in the Middle East and that interbreeding may have contributed Neanderthal genes to palaeolithic and ultimately modern Eurasians and Oceanians.
An important difference between Europe and other parts of the inhabited world was the northern latitude. Archaeological evidence suggests humans, whether Neanderthal or Cro-Magnon, reached sites in Arctic Russia by 40,000 years ago.
Around 20,000 BC, 10,000 years after the Neanderthal extinction, the Last Glacial Maximum took place forcing northern hemisphere inhabitants to migrate to several shelters until the end of this period came.
The resulting populations, whether interbred with Neanderthals or not, are then presumed to have resided in those hypothetical refuges during the LGM to ultimately reoccupy Europe where archaic historical populations are considered their descendents. An alternate view is that modern European populations have descended from Neolithic populations in the Middle East that have been well documented in this area.
The debate surrounding the origin of Europeans has been worded in terms of cultural diffusion versus demic diffusion. Archeological evidence and genetic evidence strongly support demic diffusion, that a population spread from the Middle East over the last 12,000 years. A scientific genetic concept called the Time to Most Recent Common Ancestor or TMRCA has been used to refute the demic diffusion in favour of cultural diffusion.
Interbreeding hypotheses
Neanderthals & Denisovans – Interbreding with the ancestors of present-day modern humans
The Neanderthals are a now-extinct species or subspecies within the genus Homo and closely related to modern humans. They are known from fossil specimens dating to the Pleistocene period and found in Europe and parts of western and central Asia. The term “Neanderthal”, a shortening of “Neanderthal man”, is sometimes spelled Neandertal, the modern spelling of the name of the Neander Valley in Germany where the species was first discovered.
Neanderthals are classified alternatively as a subspecies of Homo sapiens (Homo sapiens neanderthalensis) or as a separate human species (Homo neanderthalensis). The first proto-Neanderthal traits appeared in Europe as early as 600,000–350,000 years ago. Proto-Neanderthal traits are occasionally grouped with another phenetic species, such as Homo heidelbergensis, or a migrant form, Homo rhodesiensis.
Neanderthals evolved from early Homo along a path either identical or very similar to modern man, deriving from a chimp-like ancestor between five and 10 million years ago. Neanderthals are related to Australopithecus, H. habilis, and H. ergaster; however, the exact descent remains uncertain. The last common ancestor between anatomically modern humans and Neanderthals appears to be Homo rhodesiensis, typified by an archaic human fossil (Broken hill 1, Kabwe 1) discovered in Northern Rhodesia (now Zambia) in 1921.
Homo rhodesiensis arose in Africa an estimated 0.7 to 1 million years ago. The earliest estimates for Homo rhodesiensis reaching Europe are approximately 800 thousand years ago when a type of human referred to as Homo antecessor or H. cepranensis already inhabited the region.
These two human types may be forerunners to the European H. heidelbergensis; however, stone tools dating from 1.2 to 1.56 million years ago of an unknown creator have been discovered in south-western Europe. The evidence at the Sima de los Huesos in the Atapuerca cave system on the Iberian Peninsula suggests Homo heidelbergensis was already in Europe by 600,000 years ago.
Denisova hominins, or Denisovans, are Paleolithic-era members of the genus Homo that may belong to a previously unknown species of human. In March 2010, scientists announced the discovery of a finger bone fragment of a juvenile female that lived about 41,000 years ago, found in the remote Denisova Cave in the Altai Mountains in Siberia, a cave which has also been inhabited by Neanderthals and modern humans. A tooth and toe bone belonging to different members of the same population have since been found.
At that time, you’d expect to find either modern humans or Neanderthals living in Eurasia. But the finger bone’s DNA didn’t match human DNA or Neanderthal DNA. Some other kind of hominid must have also been living in the region.
Analysis of the mitochondrial DNA (mtDNA) of the finger bone showed it to be genetically distinct from the mtDNAs of Neanderthals and modern humans. Subsequent study of the nuclear genome from this specimen suggests this group shares a common origin with Neanderthals.
The Denisovans ranged from Siberia to Southeast Asia, and they lived among and interbred with the ancestors of some present-day modern humans, with up to 6% of the DNA of Melanesians and Australian aborigines, Polynesians and other people of Oceania also had a Denisovan heritage. Now it appears that Southeast Asians do as well. Denisovan DNA may account for about 1 percent of modern Southeast Asian DNA. Similar analysis of a toe bone discovered in 2011 is underway.
Molecular phylogenetic analysis of Neanderthals and a sister-group, the Denisovans, suggests a divergence time of approximately 800,000 thousand years ago, with the Denisovans diverging from the Neanderthals about 640,000 years ago.
An alternative to extinction is that Neanderthals were absorbed into the Cro-Magnon population by interbreeding. This would be counter to strict versions of the Recent African Origin, since it would imply that at least part of the genome of Europeans would descend from Neanderthals.
The most vocal proponent of the hybridization hypothesis is Erik Trinkaus of Washington University. Trinkaus claims various fossils as hybrid individuals, including the “child of Lagar Velho”, a skeleton found at Lagar Velho in Portugal dated to about 24,000 years ago. In a 2006 publication co-authored by Trinkaus, the fossils found in 1952 in the cave of Peștera Muierii, Romania, are likewise claimed as hybrids.
Genetic research has confirmed that some admixture took place. The genomes of all non-Africans include portions that are of Neanderthal origin, due to interbreeding between Neanderthals and the ancestors of Eurasians in Northern Africa or the Middle East prior to their spread. Rather than absorption of the Neanderthal population, this gene flow appears to have been of limited duration and limited extent.
An estimated 1 to 4 percent of the DNA in Europeans and Asians (French, Chinese and Papua probands) is non-modern, and shared with ancient Neanderthal DNA rather than with Sub-Saharan Africans (Yoruba and San probands). This is thought to have occurred between 80,000 and 50,000 years ago, shortly after (or perhaps before) the proto-Eurasians emigrated from Africa, while they were still one population
Nonetheless, more recent genetic studies seem to suggest that modern humans may have mated with “at least two groups” of ancient humans: Neanderthals and Denisovans.
While modern humans share some nuclear DNA with the extinct Neanderthals, the two species do not share any mitochondrial DNA, which in primates is always maternally transmitted. This observation has prompted the hypothesis that whereas female humans interbreeding with male Neanderthals were able to generate fertile offspring, the progeny of female Neanderthals who mated with male humans were either rare, absent or sterile.
The youngest Neanderthals include the Vindija Cave fossils in Croatia, which are between 33,000 and 32,000 years old. No definite specimens younger than 30,000 years ago have been found, but evidence of fire by Neanderthals in Gibraltar indicate they may have survived there until 24,000 years ago. Cro-Magnon or early modern human skeletal remains with “Neanderthal traits” were found in Lagar Velho (Portugal), dated to 24,500 years ago and interpreted as indications of extensively admixed populations.
The idea that our ancestors mated with other species may not be too shocking. Species today will mate with other closely related species if they come across each other in nature (or captivity). This occurs among olive baboons and hamadryas baboons that have overlapping ranges in Ethiopia. The idea probably seems surprising because it’s hard to imagine we once shared the planet with beings so similar to us. What was it like to meet other human-like individuals who weren’t quite human?
While interbreeding is viewed as the most parsimonious interpretation of the genetic discoveries, the authors point out they cannot conclusively rule out an alternative scenario, in which the source population of non-African modern humans was already more closely related to Neanderthals than other Africans were, due to ancient genetic divisions within Africa.
The story of our past inter-species matings is far from complete. We still don’t know who the Denisovans really were. Today, the fragment of the finger bone and the molar tooth are the sole fossils that scientists have assigned to the group. It’s impossible to say what physical features distinguished the species. But it is possible we’ve already found other Denisovan fossils. Denisovans could belong to a species whose DNA we’ve never been able to analyze, such as Homo heidelbergensis. And there are some hominid fossils in China that are hard to fit into any of the known species. If we could read their DNA, perhaps it would reveal they were Denisovans, too.
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