THE STORY OF HUMAN EVOLUTION
Finally, after about 500 million years of evolving multicellular organisms, including many severe mass extinctions and climate changes, the first member of the genus Homo appeared in Africa some 4 million years ago. Intelligent life as we know it is less than 1 million years old and accounts for less than approximately 0.02% of the Earth’s history.
The Swedish botanist Carl Linnaeus (1707-1778) was the father of modern taxonomy by his publication of The System of Nature in 1735. He placed humans among the primates and used binomial nomenclature to classify us as Homo Sapiens.
Thus, modern humans belong to [1]:
- the superkingdom of Eukaryota (multicellular organisms whose cells have a nucleus);
- the kingdom of Animalia;
- the phylum of Chordata (backboned animals);
- the class of mammals or Mammalia;
- the order of primates;
- the superfamily Hominoidea (includes humans and the apes – chimpanzees, gorillas, gibbons and orangutans);
- the family Homininae (the only primates customarily walking on two legs, which includes humans, the only living members of the hominines, and also their extinct ancestors of the last 4 or 5 million years);
- the genus Homo; and
- the species sapiens.
[1] Christian, Maps of Time, 121. This categorisation derives from the modern classification described in Roger Lewin, Human Evolution: An Illustrated Introduction, 4th ed. (Oxford, Blackwell, 1999), p 43: Christian, op cit, Chapter 5, footnote 29. On Linnaeus and where mankind fits in generally, see the Last Universal Common Ancestor graphic on the Big History Project at https://www.bighistoryproject.com/chapters/3#tree-of-life and the discussion on LUCA at /descent-from-a-common-ancestor.html
Homo sapiens viewed as a primate
A primate is a mammal of the order Primates, which includes the anthropoids and prosimians, characterised by refined development of the hands and feet, a shortened snout, and a large brain. The group contains all lemurs, monkeys, and apes, including humans. So where do humans roost on the primate family tree?
Further sub-species categorisation, each the subject of elaboration in future pages, is described in the following Smithsonian graphic, revealing that a surprising number of early human species evolved and went extinct during the period of in excess of 6 million years described.
Source: Smithsonian Exhibition, “Life and the Oceans”, October 2010.
Too small to read? Then, from the most ancient (the lower rungs of the ladder) up:
Genus/species Tenure[1]
Sahelanthropus tchadensus; Orrorin tugenensis 6 mya
Ardipithecus group
Ardipithecus kadabba; Ardipithecus ramidus 5.6-4.4 mya
These earliest humans are our closest links to other primates. They evolved in Africa and took the first steps to walking upright.
Australopithecus group
Australopithecus anamensis; Australopithecus afarensis (‘Lucy’) 3 to 4 Mya
Australopithecus garhi;
Australopithecus africanus 2 to 3 mya
Australopithecus sediba 1.78- 1.95 mya
Species in this group of early humans walked upright on a regular basis, but they still climbed trees too.
Paranthropus group
Paranthropus aethiopicus; Paranthropus robustus;
Paranthropus boisei broadly 2 to 3 Mya
Large teeth and powerful jaws enabled this group of early humans to feed on a variety of foods.
Homo group (and Neanderthals, our cousins, by invitation)
Homo rudofensis; Homo habilis 2 Mya
Homo erectus 1 to 2 Mya
Homo heidelbergensis[2] 500,000 yrs to 1 Mya
Homo naledi 236,000 to 335,000 yrs ago [3]
Homo neanderthalensis 230,000 - 28,000 yrs ago
Homo floresiensis 95,000-50,000 yrs ago
(see next page for extinction date)
Like modern humans, other species in this group had large brains and used tools. Members of this group were the first to expand beyond Africa
And today, at the apex of the tree, at least for the time being:
Homo sapiens the last 150,000 years
Or so we thought!
In 1961, fossil finds were made at the barite mining operation at the Jebel Irhoud massif in Morocco, about 100 kms west of Marrakesh. These were originally thought to be Neanderthal in origin , but were later classified as H. sapiens and eventually redated to about 160,000 years ago. More recent finds in the same area, including skull and lower jaw bones, stone tools and the remains of animals the species hunted have now been dated, by reference to the rock layer in which they were found, to between 350,000 and 280,000 years ago, pushing back the origin of our species by more than 100,000 years and challenging leading ideas about where and when our lineage evolved. Needless to say these classifications have been attended by some dissent. Before this, the oldest commonly accepted traces of our species were 195,000 year old remains from the site of Omo Kibish and 160,000 year old fossils from Herto, both in Ethiopia.[4]
Two distinct theories [5]
In light of these and other discoveries, there now appear to be two distinct theories regarding the manner in which H. sapiens emerged as a species. The first is the so-called Recent African Origin hypothesis which argues that H. sapiens arose in either eastern or southern Africa within the past 200,000 years and subsequently replaced archaic hominin species around the globe without interbreeding with them to any significant degree. The view holds that H. sapiens arose relatively recently in more or less its current form in a single region of Africa and spread out from there into the rest of the Old World, supplanting the Neanderthals and other archaic human species it encountered along the way. There was no appreciable interspecies fraternizing, just wholesale replacement of the old guards by the clever newcomer, whose ascendancy seemed inevitable.
The more recent alternative hypothesis is the Multiregional Evolution model, which holds that modern H. sapiens evolved from Neanderthals and other archaic human populations throughout the Old World, which were connected through migration and mating. This view postulates that H. sapiens originated far earlier than previously thought, reaching back nearly two million years, possibly in locations across Africa instead of a single region, and that some of its distinguishing traits—including aspects of the brain—evolved piecemeal, and that H. sapiens actually did mingle with the other human species it encountered and that interbreeding with these other human species contributed to, and may indeed have been. a crucial factor in our success.
By the early 2000s, the evidence seemed to favour the Recent African Origin. However, many archaeologists now think that the start of a cultural phase known as the Middle Stone Age (MSA) heralded the emergence of people who were beginning to think like us, and that some people who made MSA tools also made items associated with symbolic behaviour, including shell beads for jewellery and pigment for painting. This approach heralded problems for the Recent African hypothesis:
As Kate Wong points out in her article, all this culminated in a paper published online in July 2018 in Trends in Ecology & Evolution, by archaeologist Eleanor Scerri of the University of Oxford and a large interdisciplinary group of co-authors, postulating the case for the so-called African Multiregionalism model of H. sapiens evolution, and noting along the way that the earliest putative members of our species - the Jebel Irhoud fossils from Morocco, the Herto and Omo Kibish fossils from Ethiopia, and a partial skull from Florisbad, South Africa—all look far more different from one another than people today do.
The end result is that the emergence of H. sapiens may be more of a pan-African phenomenon, and, rather than evolving as a small population in a particular region of Africa, our species “may have emerged from a large population that was subdivided into smaller groups distributed across the vast African continent that were often semi-isolated for thousands of years at a time by distance and by ecological barriers such as deserts. Those bouts of solitude allowed each group to develop its own biological and technological adaptations to its own niche, be it an arid woodland or a savannah grassland, a tropical rain forest or a marine coast. Every so often, however, the groups came into contact with one another, allowing for both genetic and cultural exchange that fed the evolution of our lineage”.[6]
[1] Dates possibly subject to revision as the result of the new molecular clock technique referred to by Catherine Brahic in “Our True dawn”, New Scientist. 24 November 2012, 34.
[2] The new molecular clock technique would tend to suggest 500,000 years: (2Ibid at 37. As noted on the Denisovan page, it has also been suggested that Homo heidelbergensis is the "most likely progenitor" of all three types: Neanderthals and Denisovans on the one hand and modern humans on the other. Our human ancestors diverged from theirs about 500,000 years ago The other two species were closely related, and perhaps diverged from each other about 250,000 years ago: “The case of the missing ancestor”, Scientific American, July 2013, 90 at 98.
[3] /fossil-finds.html See also The Washington Post, "Fossils found in African cave are new species of human kin, say scientists", 10 September 2015; Nikki Phillips, "New species of man.. make no bones about it", SMH, Sept 12-13 2015.
[4] The full story of the Jebel Irhoud finds is told in Kate Wong's article "The oldest Homo sapiens?", Scientific American, September 2017, 13-14. The site of the Omo Kibish finds is indicated by red numeral (1) on the National Geographic map lower down the page.
[5] This is an edited version of Kate Wong's article "Last Hominin standing", which appeared in the September 2018 edition of the Scientific American at 55-61.
[6] Ibid.
Naturally enough, it not easy to slot or classify individual fossil finds into a particular branch in the line of human pre-species. Remember that the Homininae are a subfamily of the Hominoidea, the great apes. They include only our own immediate ancestors. Their story begins at the transition from the Miocene to the Pliocene eras between 5 and 6 million years ago. The construction of that story begins with the realisation, based on molecular dating techniques, that about 6 million years ago there existed somewhere in Africa an animal that was the ancestor of both modern chimps and modern humans. Since then, in a series of adaptive radiations, a large number of different species of hominines has appeared – perhaps as many as 20 or 30.
Whereas 30 years ago, the difficulty was to find any hominine remains, today the difficulty is to decide which of the many species we know of lies on the line that evolved into modern humans, and for a modern paleontologist, the holy grail is to find the remains of the species from which both chimps and humans are descended[1].
Whatever may have been the origins of humankind in Africa, the species then moved across the globe in a series of adaptive radiations[2]
Note: The numbers in red and in brackets - (1),(2) etc below refer to the numbered journeys which appear in the Shreeve article National Geographic maps lower down the page.
Too small to read? Then, from the most ancient (the lower rungs of the ladder) up:
Genus/species Tenure[1]
Sahelanthropus tchadensus; Orrorin tugenensis 6 mya
Ardipithecus group
Ardipithecus kadabba; Ardipithecus ramidus 5.6-4.4 mya
These earliest humans are our closest links to other primates. They evolved in Africa and took the first steps to walking upright.
Australopithecus group
Australopithecus anamensis; Australopithecus afarensis (‘Lucy’) 3 to 4 Mya
Australopithecus garhi;
Australopithecus africanus 2 to 3 mya
Australopithecus sediba 1.78- 1.95 mya
Species in this group of early humans walked upright on a regular basis, but they still climbed trees too.
Paranthropus group
Paranthropus aethiopicus; Paranthropus robustus;
Paranthropus boisei broadly 2 to 3 Mya
Large teeth and powerful jaws enabled this group of early humans to feed on a variety of foods.
Homo group (and Neanderthals, our cousins, by invitation)
Homo rudofensis; Homo habilis 2 Mya
Homo erectus 1 to 2 Mya
Homo heidelbergensis[2] 500,000 yrs to 1 Mya
Homo naledi 236,000 to 335,000 yrs ago [3]
Homo neanderthalensis 230,000 - 28,000 yrs ago
Homo floresiensis 95,000-50,000 yrs ago
(see next page for extinction date)
Like modern humans, other species in this group had large brains and used tools. Members of this group were the first to expand beyond Africa
And today, at the apex of the tree, at least for the time being:
Homo sapiens the last 150,000 years
Or so we thought!
In 1961, fossil finds were made at the barite mining operation at the Jebel Irhoud massif in Morocco, about 100 kms west of Marrakesh. These were originally thought to be Neanderthal in origin , but were later classified as H. sapiens and eventually redated to about 160,000 years ago. More recent finds in the same area, including skull and lower jaw bones, stone tools and the remains of animals the species hunted have now been dated, by reference to the rock layer in which they were found, to between 350,000 and 280,000 years ago, pushing back the origin of our species by more than 100,000 years and challenging leading ideas about where and when our lineage evolved. Needless to say these classifications have been attended by some dissent. Before this, the oldest commonly accepted traces of our species were 195,000 year old remains from the site of Omo Kibish and 160,000 year old fossils from Herto, both in Ethiopia.[4]
Two distinct theories [5]
In light of these and other discoveries, there now appear to be two distinct theories regarding the manner in which H. sapiens emerged as a species. The first is the so-called Recent African Origin hypothesis which argues that H. sapiens arose in either eastern or southern Africa within the past 200,000 years and subsequently replaced archaic hominin species around the globe without interbreeding with them to any significant degree. The view holds that H. sapiens arose relatively recently in more or less its current form in a single region of Africa and spread out from there into the rest of the Old World, supplanting the Neanderthals and other archaic human species it encountered along the way. There was no appreciable interspecies fraternizing, just wholesale replacement of the old guards by the clever newcomer, whose ascendancy seemed inevitable.
The more recent alternative hypothesis is the Multiregional Evolution model, which holds that modern H. sapiens evolved from Neanderthals and other archaic human populations throughout the Old World, which were connected through migration and mating. This view postulates that H. sapiens originated far earlier than previously thought, reaching back nearly two million years, possibly in locations across Africa instead of a single region, and that some of its distinguishing traits—including aspects of the brain—evolved piecemeal, and that H. sapiens actually did mingle with the other human species it encountered and that interbreeding with these other human species contributed to, and may indeed have been. a crucial factor in our success.
By the early 2000s, the evidence seemed to favour the Recent African Origin. However, many archaeologists now think that the start of a cultural phase known as the Middle Stone Age (MSA) heralded the emergence of people who were beginning to think like us, and that some people who made MSA tools also made items associated with symbolic behaviour, including shell beads for jewellery and pigment for painting. This approach heralded problems for the Recent African hypothesis:
- The earliest dates for the MSA were more than 250,000 years ago—far older than those for the earliest H. sapiens fossils at less than 200,000 years ago.
- Subsequent ancient genome studies confirmed that Neanderthals contributed to the modern human gene pool, as did other archaic humans, showing that H. sapiens and Neanderthals did interbreed after all, at least on occasion.
- Further, contrary to the notion that H. sapiens originated within the past 200,000 years, the ancient DNA evidence suggested that Neanderthals and H. sapiens diverged from their common ancestor considerably earlier than that, perhaps upward of half a million years ago.
- The Jebel Irhoud fossils in conjunction with the discovery of some MSA tools pushed back the fossil evidence of our species by more than 100,000 years linking it to the earliest known appearance of the MSA and signifying that the total H. sapiens package did not coalesce until sometime between 100,000 and 40,000 years ago.
As Kate Wong points out in her article, all this culminated in a paper published online in July 2018 in Trends in Ecology & Evolution, by archaeologist Eleanor Scerri of the University of Oxford and a large interdisciplinary group of co-authors, postulating the case for the so-called African Multiregionalism model of H. sapiens evolution, and noting along the way that the earliest putative members of our species - the Jebel Irhoud fossils from Morocco, the Herto and Omo Kibish fossils from Ethiopia, and a partial skull from Florisbad, South Africa—all look far more different from one another than people today do.
The end result is that the emergence of H. sapiens may be more of a pan-African phenomenon, and, rather than evolving as a small population in a particular region of Africa, our species “may have emerged from a large population that was subdivided into smaller groups distributed across the vast African continent that were often semi-isolated for thousands of years at a time by distance and by ecological barriers such as deserts. Those bouts of solitude allowed each group to develop its own biological and technological adaptations to its own niche, be it an arid woodland or a savannah grassland, a tropical rain forest or a marine coast. Every so often, however, the groups came into contact with one another, allowing for both genetic and cultural exchange that fed the evolution of our lineage”.[6]
[1] Dates possibly subject to revision as the result of the new molecular clock technique referred to by Catherine Brahic in “Our True dawn”, New Scientist. 24 November 2012, 34.
[2] The new molecular clock technique would tend to suggest 500,000 years: (2Ibid at 37. As noted on the Denisovan page, it has also been suggested that Homo heidelbergensis is the "most likely progenitor" of all three types: Neanderthals and Denisovans on the one hand and modern humans on the other. Our human ancestors diverged from theirs about 500,000 years ago The other two species were closely related, and perhaps diverged from each other about 250,000 years ago: “The case of the missing ancestor”, Scientific American, July 2013, 90 at 98.
[3] /fossil-finds.html See also The Washington Post, "Fossils found in African cave are new species of human kin, say scientists", 10 September 2015; Nikki Phillips, "New species of man.. make no bones about it", SMH, Sept 12-13 2015.
[4] The full story of the Jebel Irhoud finds is told in Kate Wong's article "The oldest Homo sapiens?", Scientific American, September 2017, 13-14. The site of the Omo Kibish finds is indicated by red numeral (1) on the National Geographic map lower down the page.
[5] This is an edited version of Kate Wong's article "Last Hominin standing", which appeared in the September 2018 edition of the Scientific American at 55-61.
[6] Ibid.
Naturally enough, it not easy to slot or classify individual fossil finds into a particular branch in the line of human pre-species. Remember that the Homininae are a subfamily of the Hominoidea, the great apes. They include only our own immediate ancestors. Their story begins at the transition from the Miocene to the Pliocene eras between 5 and 6 million years ago. The construction of that story begins with the realisation, based on molecular dating techniques, that about 6 million years ago there existed somewhere in Africa an animal that was the ancestor of both modern chimps and modern humans. Since then, in a series of adaptive radiations, a large number of different species of hominines has appeared – perhaps as many as 20 or 30.
Whereas 30 years ago, the difficulty was to find any hominine remains, today the difficulty is to decide which of the many species we know of lies on the line that evolved into modern humans, and for a modern paleontologist, the holy grail is to find the remains of the species from which both chimps and humans are descended[1].
Whatever may have been the origins of humankind in Africa, the species then moved across the globe in a series of adaptive radiations[2]
Note: The numbers in red and in brackets - (1),(2) etc below refer to the numbered journeys which appear in the Shreeve article National Geographic maps lower down the page.
Scientists have long held that modern humans originated in Africa for the simple reason that, that is where most, and the oldest, bones have been found; but geneticists have come to the same conclusion by looking at Africa’s vast genetic diversity, which could only have arisen as DNA mutated over millennia.
What seems to be relatively uncontested, if at all, is that:
However, there is less consensus about the routes our ancestors took as they migrated out of Africa and thence around the planet. Some early migrations stalled but left behind evidence such as a human skull from 92,000 years ago at Qafzeh, Israel (considered on a separate page). They may have taken a northern route through the Nile Valley into the Middle East, but others who left Africa tens of thousands of years later could also have taken a different route: across the southern end of the Red Sea, (1), (2) and scientists say these more recent wanderers gave rise to the 5.5 billion or so humans living outside Africa today.
What now seems virtually certain is that at a remarkably recent date, probably between 50,000 and 70,000 years ago, one small wavelet from Africa lapped up onto the shores of western Asia. All non-Africans share genetic markers carried by those first emigrants, who may have numbered just a thousand people.
Tools, symbols, language may have accompanied these migrations
Some archaeologists think the migration out of Africa marked a revolution in behavior that also included more sophisticated tools, wider social networks, and the first art and body ornaments. Perhaps some kind of neurological mutation had led to spoken language and made our ancestors fully modern, setting a small band of them on course to colonize the world. Other scientists see finely wrought tools and other traces of modern behavior scattered around Africa long before those first steps outside the continent. Toolmaking itself may have posed a formidable enough challenge to our ancestors that it spurred the development of brain size and human language: /climate-change-toolmaking-and-language-as-factors-influencing-hominin-diversity.html
Discrete paths into Asia
Whatever tools and cognitive skills accompanied the emigrants, two paths lay open into Asia: one led up the Nile Valley, across the Sinai Peninsula, and north into the Levant. But another also beckoned. Seventy thousand years ago the Earth was entering the last ice age, and sea levels were sinking as water was locked up in glaciers. At its narrowest, the mouth of the Red Sea between the Horn of Africa and Arabia would have been only a few miles wide. Using primitive watercraft, modern humans could have crossed over while barely getting their feet wet. And, once in Asia, genetic evidence suggests, the population again split. (4)
One group stalled temporarily in the Middle East, while the other followed the coast around the Arabian Peninsula, India, and beyond. Each generation may have pushed just a couple of miles farther. The movement was probably imperceptible, but over the millennia, a few steps a year and a few hops by boat added up, to such an extent that the wanderers had reached southeastern Australia by 45,000 years ago, when a man was buried at a site called Lake Mungo. Artifact-bearing soil layers beneath the burial could be as old as 50,000 years—the earliest evidence of modern humans far from Africa. (3)
No physical trace of these people has been found along the 8,000 miles from Africa to Australia—all may have vanished as the sea rose after the Ice Age. But a genetic trace endures. A few indigenous groups on the Andaman Islands near Myanmar, in Malaysia, and in Papua New Guinea—as well as almost all Australian Aborigines—carry signs of an ancient mitochondrial lineage, a trail of genetic bread crumbs dropped by the early migrants.
People in the rest of Asia and Europe share different but equally ancient mtDNA and Y-chromosome lineages, marking them as descendants of the other, stalled branch of the African exodus. At first, rough terrain and the Ice Age climate blocked further progress. Europe, moreover, was a stronghold of the Neanderthals, descendants of a much earlier migration of pre-modern humans out of Africa.
Finally, perhaps 40,000 years ago, modern humans advanced into the Neanderthals' territory. Overlapping layers of Neanderthal and early modern human artifacts at a cave in France suggest that the two kinds of humans could have met. Once modern humans and their sophisticated toolmaking spread into Europe, the formerly ubiquitous Neanderthals were squeezed into ever shrinking pockets of habitation that eventually petered out completely.
About the same time as modern humans pushed into Europe, some of the same group that had paused in the Middle East spread east into Central Asia reaching southern Siberia as early as 40,000 years ago. (5) As populations diverged and became isolated, their genetic lineages likewise branched and rebranched, but the isolation was rarely if ever complete.
The Americas
So far as the Americas are concerned, most scientists agree that today's Native Americans descend from ancient Asians who crossed from Siberia to Alaska in the last ice age, when low sea level would have exposed a land bridge between the continents. But there is much debate about when they came and where they originated in Asia. For decades the first Americans were thought to have arrived around 13,000 years ago as the Ice Age eased, opening a path through the ice covering Canada. But some archaeologists claimed to have evidence for an earlier arrival, and two early sites withstood repeated criticism: the Meadow-croft Shelter in Pennsylvania, now believed to be about 16,000 years old, and Monte Verde in southern Chile, more than 14,000 years old.
The available genetic evidence presently suggests that the first people arrived in the Americas between 20,000 and 15,000 years ago, when sea levels were low and land connected Siberia to Alaska. Ice sheets would have covered the interior of North America, forcing the new arrivals, perhaps just a few hundred people, to travel down the west coast. Then, pushed by population growth or pulled by the lure of game, people spread to the tip of South America in as little as a thousand years. So, when European explorers set sail 700 years ago, the lands they "discovered" were are from being “terra nullius”. They were already full of people. The result is that when unravelled, the tangled knot of our global genetic diversity today leads us all back to a recent yesterday, together in Africa. (6)
What seems to be relatively uncontested, if at all, is that:
- about 25 million years ago, the family of primates known as the hominoids, or human-like animals, first surfaced in Africa;
- the particular line to which humans belong then diverged from that of the gorillas and chimpanzees between five and seven million years ago – although we still share 98.4 per cent of our genetic make-up with modern chimps;
- roughly 200,000 years ago, modern humans, anatomically indistinguishable from us, emerged in Africa, and thereafter they left, for reasons which will be considered later.
However, there is less consensus about the routes our ancestors took as they migrated out of Africa and thence around the planet. Some early migrations stalled but left behind evidence such as a human skull from 92,000 years ago at Qafzeh, Israel (considered on a separate page). They may have taken a northern route through the Nile Valley into the Middle East, but others who left Africa tens of thousands of years later could also have taken a different route: across the southern end of the Red Sea, (1), (2) and scientists say these more recent wanderers gave rise to the 5.5 billion or so humans living outside Africa today.
What now seems virtually certain is that at a remarkably recent date, probably between 50,000 and 70,000 years ago, one small wavelet from Africa lapped up onto the shores of western Asia. All non-Africans share genetic markers carried by those first emigrants, who may have numbered just a thousand people.
Tools, symbols, language may have accompanied these migrations
Some archaeologists think the migration out of Africa marked a revolution in behavior that also included more sophisticated tools, wider social networks, and the first art and body ornaments. Perhaps some kind of neurological mutation had led to spoken language and made our ancestors fully modern, setting a small band of them on course to colonize the world. Other scientists see finely wrought tools and other traces of modern behavior scattered around Africa long before those first steps outside the continent. Toolmaking itself may have posed a formidable enough challenge to our ancestors that it spurred the development of brain size and human language: /climate-change-toolmaking-and-language-as-factors-influencing-hominin-diversity.html
Discrete paths into Asia
Whatever tools and cognitive skills accompanied the emigrants, two paths lay open into Asia: one led up the Nile Valley, across the Sinai Peninsula, and north into the Levant. But another also beckoned. Seventy thousand years ago the Earth was entering the last ice age, and sea levels were sinking as water was locked up in glaciers. At its narrowest, the mouth of the Red Sea between the Horn of Africa and Arabia would have been only a few miles wide. Using primitive watercraft, modern humans could have crossed over while barely getting their feet wet. And, once in Asia, genetic evidence suggests, the population again split. (4)
One group stalled temporarily in the Middle East, while the other followed the coast around the Arabian Peninsula, India, and beyond. Each generation may have pushed just a couple of miles farther. The movement was probably imperceptible, but over the millennia, a few steps a year and a few hops by boat added up, to such an extent that the wanderers had reached southeastern Australia by 45,000 years ago, when a man was buried at a site called Lake Mungo. Artifact-bearing soil layers beneath the burial could be as old as 50,000 years—the earliest evidence of modern humans far from Africa. (3)
No physical trace of these people has been found along the 8,000 miles from Africa to Australia—all may have vanished as the sea rose after the Ice Age. But a genetic trace endures. A few indigenous groups on the Andaman Islands near Myanmar, in Malaysia, and in Papua New Guinea—as well as almost all Australian Aborigines—carry signs of an ancient mitochondrial lineage, a trail of genetic bread crumbs dropped by the early migrants.
People in the rest of Asia and Europe share different but equally ancient mtDNA and Y-chromosome lineages, marking them as descendants of the other, stalled branch of the African exodus. At first, rough terrain and the Ice Age climate blocked further progress. Europe, moreover, was a stronghold of the Neanderthals, descendants of a much earlier migration of pre-modern humans out of Africa.
Finally, perhaps 40,000 years ago, modern humans advanced into the Neanderthals' territory. Overlapping layers of Neanderthal and early modern human artifacts at a cave in France suggest that the two kinds of humans could have met. Once modern humans and their sophisticated toolmaking spread into Europe, the formerly ubiquitous Neanderthals were squeezed into ever shrinking pockets of habitation that eventually petered out completely.
About the same time as modern humans pushed into Europe, some of the same group that had paused in the Middle East spread east into Central Asia reaching southern Siberia as early as 40,000 years ago. (5) As populations diverged and became isolated, their genetic lineages likewise branched and rebranched, but the isolation was rarely if ever complete.
The Americas
So far as the Americas are concerned, most scientists agree that today's Native Americans descend from ancient Asians who crossed from Siberia to Alaska in the last ice age, when low sea level would have exposed a land bridge between the continents. But there is much debate about when they came and where they originated in Asia. For decades the first Americans were thought to have arrived around 13,000 years ago as the Ice Age eased, opening a path through the ice covering Canada. But some archaeologists claimed to have evidence for an earlier arrival, and two early sites withstood repeated criticism: the Meadow-croft Shelter in Pennsylvania, now believed to be about 16,000 years old, and Monte Verde in southern Chile, more than 14,000 years old.
The available genetic evidence presently suggests that the first people arrived in the Americas between 20,000 and 15,000 years ago, when sea levels were low and land connected Siberia to Alaska. Ice sheets would have covered the interior of North America, forcing the new arrivals, perhaps just a few hundred people, to travel down the west coast. Then, pushed by population growth or pulled by the lure of game, people spread to the tip of South America in as little as a thousand years. So, when European explorers set sail 700 years ago, the lands they "discovered" were are from being “terra nullius”. They were already full of people. The result is that when unravelled, the tangled knot of our global genetic diversity today leads us all back to a recent yesterday, together in Africa. (6)
[1] Christian, Maps of Time, 154.
[2] Source for this material: James Shreeve, “The greatest journey ever told – the trail of our DNA”, National Geographic, March 2006, 60-69.
Shreeve's chronology may be considered uncontroversial from a conventional out of Africa viewpoint. In fact Curtis W Marean, a professor of Human Evolution and Social Change at Arizona, in a recently published article in the Scientific American[1] accepts uncritically the bones of such a chronology, if you’ll forgive the expression, with only minor modifications. The dating sequence below should now be considered subject to the archaeological and genetic evidence on the Australian aborigine noted below above footnote [5.1]:
- about 100,000 years ago one group made a brief foray into the Middle east, but failed to go on with it. They “needed an edge which they did not yet have”, he adds.
- around 70,000 years ago, a “small founder population” left their homeland again and pressed into Eurasia where they encountered other closely related human species: the Neanderthals in Western Europe and the Denisovans.in Asia. These went extinct, although their DNA persists in people today as the result of occasional interbreeding between the groups;
- They reached Australia by at least 45,000 years ago and “quickly filled the continent, sprinting across it with spear-throwers and fire”; about 40,000 years ago, they found and crossed a land bridge to Tasmania.
- Further north, around 35,000 years ago another group travelling north-east penetrated Siberia and radiated across the lands encircling the North Pole. They entered what is now the north American continent, perhaps around 14,000 years ago and within a few thousand years they reached southernmost South America.
However, chronology does not lay at the heart of Marean’s article. He suggests that none of the hypotheses advanced thus far to explain H sapiens successful incursions into the world at large (larger brain, more advanced technology, the effects of climate change on the Neanderthals and others)[2] provides a comprehensive theory that can explain the full extent of H. sapiens reach. Indeed, he says that “these theories have mostly been proffered as explanations for records of H sapiens activities in particular regions such as western Europe”, that this piecemeal approach has misled scientists, and that this great human diaspora needs to be investigated as a single research question.
Based on his work and research in the Pinnacle Point region of the African continent, he suggests that when climate conditions on the South African continent deteriorated about 160,000 years ago leaving much of inland Africa uninhabitable, some members of the species sought refuge on the southern coast and learned how to exploit the rich shellfish beds there for food[3].
This then led, he says, to the crux of the matter|: the evolution of a ”genetically coded proclivity for co-operation” between unrelated individuals – the better to defend the shellfish beds against interlopers. “The joining of this unique proclivity to our ancestors’ advanced cognitive abilities enabled them to nimbly adapt to new environments”. Singularly collaborative and socially connected, the species became ever more inventive, giving rise to an innovative game-changing technology: advanced projectile weaponry. “With the joining of projectile weapons to hyperprosocial behaviour, a spectacular new creature was born which would lead them to go forth to conquer the world, driving lesser equipped species such as the Neanderthals to extinction and much of the megafauna in the continents they invaded as well.
[1] “The most invasive species of all”, August 2015, 22-29.
[2] These are considered in more detail in the page below “Climate changes influencing hominim diversity”
[3] Cf Peter Spinks, “’Out of Africa’ theory of human evolution under fire”, SMH, 25 August 2014: “Archaeologists say that between about 75,000 and 55,000 years ago, a series of remarkable technological and cultural innovations occurred in southern Africa, including personal ornamentation, such as perforated shells, art in the form of engraved ochre pieces, for instance, and more effective hafted hunting weapons – and perhaps the systematic exploitation of marine fish. Such innovations probably helped modern humans to survive in less familiar environments – and to out-compete pre-existing archaic populations”: Extract from the research team’s article in the journal Quaternary International, cited in Ibid. The research team was led by anthropologist Christopher Bae of the University of Hawaii.
However, there are those for whom what may be termed 'the conventional chronology' does not sit so comfortably, and who think that....
The ‘Out of Africa’ theory needs some refining - at least as regards the timing
The recent discovery of the fragmented remains of ancient permanent teeth, one proved to have belonged to a member of the modern Homo sapiens species and 126,000 years old, in a cave called Lunadong, in China's autonomous region of Guangxi Zhuang, has profound repercussions for the ‘Out of Africa’ theory of hominin migration from that continent. The theory remains intact in substance in its broad general outlines, but the dating of the exodus may need to be pushed further back in time.
The China Lunadong tooth discovery
The conventional view of the Out of Africa theory has been that around 60,000 years ago, our human ancestors left Africa and spread across to globe to Europe in the North and across Asia in the East. However, the discovery of the 126,000 year old Lunadong tooth attributed to H. sapiens suggests that our modern human ancestors may have departed their African homelands as much as 120,000 and perhaps even 130,000 years ago[1]. "The Lunadong modern Homo sapiens teeth contribute to growing evidence that modern and/or transitional humans were likely in eastern Asia … [during] a period that some researchers have suggested no hominins were present in the region. There were probably multiple dispersals of modern humans out of Africa and into Eurasia, with some degree of interbreeding occurring."[2]
The tooth discovery also gives a clearer idea of the route our ancient forebears took after leaving Africa. "Most research currently suggests that modern humans took a southern route once they left Africa and travelled more or less along the Arabian Peninsula before arriving in south-east Asia", but "(t)here may have been a second later dispersal into north-west Asia, where those groups eventually moved into Europe and along the northern Asian route eventually arriving in Siberia and then on to the Americas," says Peter Hiscock, the Tom Austen Brown Chair of Australian Archaeology at the University of Sydney. However, the current data still indicates that Australia was probably only peopled sometime after 60,000 years ago. "The early colonisation of Australia, now documented at between 50,000 and 60,000 years ago, makes more sense if the movement of humans out of Africa was substantially earlier."
The latest find is part of a broader revision of the chronology of the "out of Africa" dispersion. "Anatomically, modern humans found in caves in Israel and dated to more than 100,000 years ago, have long suggested either multiple migrations out of Africa or else a need to revise the chronology of the dispersion."[3] In other words, the textbook version of the Out of Africa to the effect that about 60,000 years ago, humans hunted and gathered their way out of Africa and on to other parts of the world would seem to require some revision.
The Jebel Faya (UAE) Paleolithic stone tools discovery
Another and earlier study, led by Professor Hans-Peter Uerpmann of Eberhard Karls University in Tübingen, Germany, and published in the journal Science, describes findings from an eight-year archaeological excavation at Jebel Faya in the United Arab Emirates. The researchers analysed the Palaeolithic stone tools found there and concluded that they were technologically similar to instruments produced by early modern humans in east Africa. But they were notably different from tools created to the north, in the Levant and the mountains of Iran, thereby providing compelling evidence that early modern humans migrated into Arabia directly from Africa and not via the Nile Valley and the Near East, as usually suggested.[4] The direct route from east Africa to Jebel Faya crosses the southern Red Sea and the flat, waterless Nejd Plateau of the southern Arabian interior, both of which present major obstacles to human migration.
Another team member, Professor Adrian Parker of Oxford Brookes University, studied detailed records relating to sea levels and climate change for the region and concluded that the direct migration route may have been passable for brief periods in the past. Between 140,000 and 130,000 years ago, the Red Sea was about 100 metres lower than today – due to vast quantities of water being stored on land as ice during the second to last Ice Age. "So the seaway that separates east Africa from Arabia – the Bab-el-Mandab Straits – would have shrunk to roughly five to 10 kilometres in width. By about 130,000 years ago, southern Arabia was much wetter than it is now."[5]
Using a technique called luminescence dating, stone tools at Jebel Faya have been dated at about 125,000 years old This technique measures the time since sediment surrounding the artefacts was last exposed to light, allowing researchers to determine when the artefacts were buried. The dates obtained revealed that modern humans were at Jebel Faya about 125,000 years ago, immediately after the Bab al-Mandab seaway and Nejd Plateau were passable.
In other words, the recent evidence suggests modern humans left Africa, crossed the Bab-el-Mandab Straits and occupied southern Arabia by roughly 125,000 years ago. They left because the Bab-el-Mandab Straits were passable and southern Arabia was wet enough to be habitable. These conditions only occur together at the transition from the penultimate glacial to the present interglacial – that is, about 130,000 years ago. Once modern humans reached Jebel Faya, they would have needed to cross the Straits of Hormuz to reach Asia.
Or, was it "Out of Europe" rather than "Out of Africa"?
Based on two fossils of an ape-like creature which had human-like teeth found in Bulgaria and Greece, dating to 7.2 million years ago, some scientists now believe that Europe was the birthplace of mankind, not Africa, contradicting the view that our human lineage split from apes around seven million years ago in central Africa, where hominids remained for the next five million years before venturing further afield.
The two fossils, named Graecopithecus freybergi, and nicknameded ‘El Graeco', is said to indicate that our ancestors were already starting to evolve in Europe 200,000 years before the earliest African hominid, and to place the last common ancestor of both chimpanzees and humans - the so-called Missing Link - in the Mediterranean region. At that time, the researchers say that climate change had turned Eastern Europe into an open savannah which forced apes to find new food sources, sparking a shift towards bipedalism. The species was also found to be several hundred thousand years older than the oldest African hominid, Sahelanthropus tchadensis which was found in Chad. Graecopithecus is said to be not an ape, but a member of the tribe of hominins and the direct ancestor of homo. Like humans, he has wide molars and thick enamel.
The new research is published in the journal PLOS One. However other experts were more sceptical on the basis of the very substantial fossil evidence in Africa, including several partial skeletons and skulls, rather than using a single character from an isolated fossil to set against the evidence from Africa.
More evidence of multiple adaptive radiations
Meanwhile, another skull was located at a site near Apidima in southern Greece which turned out to be the oldest known modern human remains found outside of Africa. The skull was named “Apidima 1” after being found near a second skull labelled “Apidima 2” found in the 1970s. Using cutting-edge dating and reconstruction techniques, a team from Australia, Greece and Germany identified Apidima 2 as a Neanderthal, while Apidima 1 was Homo sapiens - a modern human. The team used “laser ablative” techniques to slice tiny parts off the fossils, which could then be tested using radiometric dating to determine their age. They also used 3D modelling techniques to reconstruct virtual models of the skulls, which could then be compared with other fossils visually.
Misliya cave in Israel was the site of the previous oldest modern human remains discovered outside Africa, dated to between 177,000 and 194,000 years old. The age of Apidima 1 suggests modern humans had spread out from Africa multiple times, instead of in one mass migration, and having the two skulls found so close to each other also suggested modern humans could have been living in very similar areas to Neanderthals. Genetic research shows that there may have been an influx of modern human genes in the Neanderthal genome around 200,000 years ago, but whether Europeans are actually descendants of Apidima 1 [and 2 - there are Neanderthal genes in all Europeans] is a question that will probably never be answered.
A footnote on Australian aborigine [5.1]
Genetic and archaeological evidence now shows that aboriginal people arrived in Australia some 65,000 years ago, 20,000 years before our ancestors first arrived in Europe, thus making the Australian aborigine the descendants of the first modern humans that exited Africa nearly 75,000 years ago establishing a new minimum age for the dispersal of modern humans out of Africa and across Asia. The new dates accord well with genetic analyses published in 2001 indicating that modern humans left Africa between 60,000 and 80,000 years ago, at which time there were much lower sea levels and the crossing from the islands of south east Asia was short than today. Previous estimates of aboriginal settlement in Australia ranged from 47,000 to 60,000 years. The new evidence also means that the Australian aborigine arrived on the continent before the extinction of giant Australian megafauna such as giant wombats, short-faced kangaroos and lizards.
These new findings are based on a so-called treasure trove of thousands of Aboriginal artefacts, including the oldest known ground-edge stone-age and seed grinding tools in the world, all unearthed in a Northern Territory rock shelter called Madjedbebe, surrounded by the world heritage listed Kakadu National Park. Some 11,000 artefacts were discovered in the lowest layer of the 2015 dig. Large quantities of ground ochre used for rock art were also found. Extensive dating by optically simulated luminescence methods, which estimate the time since mineral grains were last exposed to sunlight, showed a general pattern of increasing age with depth.
The weight of scientific evidence also now supports the notion that the spectacular 20,000 year old rock art from the Kimberley region in Western Australia, known as the Bradshaw paintings was painted by Aboriginal Australians who had become isolated from the rest of the world for over 50,000 years, and not a people who may have preceded them on the continent. Aborigines also have the oldest known oral history in the world, passing through some 300 generations.
So, taking all these discoveries at face value, perhaps a revised record of Out of Africa should appear something like this:
[1] Peter Spinks, “Out of Africa’ theory of human evolution under fire”, SMH, 25 August 2014. The discovery is mentioned in greater detail when considering the fossil finds in China's autonomous region of Guangxi Zhua.
[2] Extract from the research team’s article in the journal Quaternary International, cited in Ibid. The research team was led by anthropologist Christopher Bae of the University of Hawaii.
[3] Ibid.
[4] Attributed to Simon Armitage from Royal Holloway, a University of London college and cited in Ibid.
[5] Ibid.
[5.1] See https://www.dailysabah.com/history/2017/07/20/humans-arrived-in-australia-20000-years-before-europe-study-says; http://www.dailymail.co.uk/sciencetech/article-3153421/The-Australians-Aborigines-DNA-analysis-quashes-claims-unknown-race-preceded-indigenous-people-live-today.html (published 8 July 2015; 25 July 2016). For another article confidently refuting the out-of-Africa “myth”, and the whole idea of a mitochondrial Eve and Y-chromosome Adam originating in Africa, and asserting that, based on DNA evidence, Homo sapiens and the Denisovans all descended from the Australian Aborigine, see Steven Strong “researcher, author and former high school teacher” and Andy Whiteley, “ a former corporate manager turned writer, (and) editor”: https://wakeup-world.com/2013/12/16/dna-evidence-debunks-the-out-of-africa-theory-of-human-evolution/
[6] Hiscock, supra.
Meanwhile, another skull was located at a site near Apidima in southern Greece which turned out to be the oldest known modern human remains found outside of Africa. The skull was named “Apidima 1” after being found near a second skull labelled “Apidima 2” found in the 1970s. Using cutting-edge dating and reconstruction techniques, a team from Australia, Greece and Germany identified Apidima 2 as a Neanderthal, while Apidima 1 was Homo sapiens - a modern human. The team used “laser ablative” techniques to slice tiny parts off the fossils, which could then be tested using radiometric dating to determine their age. They also used 3D modelling techniques to reconstruct virtual models of the skulls, which could then be compared with other fossils visually.
Misliya cave in Israel was the site of the previous oldest modern human remains discovered outside Africa, dated to between 177,000 and 194,000 years old. The age of Apidima 1 suggests modern humans had spread out from Africa multiple times, instead of in one mass migration, and having the two skulls found so close to each other also suggested modern humans could have been living in very similar areas to Neanderthals. Genetic research shows that there may have been an influx of modern human genes in the Neanderthal genome around 200,000 years ago, but whether Europeans are actually descendants of Apidima 1 [and 2 - there are Neanderthal genes in all Europeans] is a question that will probably never be answered.
A footnote on Australian aborigine [5.1]
Genetic and archaeological evidence now shows that aboriginal people arrived in Australia some 65,000 years ago, 20,000 years before our ancestors first arrived in Europe, thus making the Australian aborigine the descendants of the first modern humans that exited Africa nearly 75,000 years ago establishing a new minimum age for the dispersal of modern humans out of Africa and across Asia. The new dates accord well with genetic analyses published in 2001 indicating that modern humans left Africa between 60,000 and 80,000 years ago, at which time there were much lower sea levels and the crossing from the islands of south east Asia was short than today. Previous estimates of aboriginal settlement in Australia ranged from 47,000 to 60,000 years. The new evidence also means that the Australian aborigine arrived on the continent before the extinction of giant Australian megafauna such as giant wombats, short-faced kangaroos and lizards.
These new findings are based on a so-called treasure trove of thousands of Aboriginal artefacts, including the oldest known ground-edge stone-age and seed grinding tools in the world, all unearthed in a Northern Territory rock shelter called Madjedbebe, surrounded by the world heritage listed Kakadu National Park. Some 11,000 artefacts were discovered in the lowest layer of the 2015 dig. Large quantities of ground ochre used for rock art were also found. Extensive dating by optically simulated luminescence methods, which estimate the time since mineral grains were last exposed to sunlight, showed a general pattern of increasing age with depth.
The weight of scientific evidence also now supports the notion that the spectacular 20,000 year old rock art from the Kimberley region in Western Australia, known as the Bradshaw paintings was painted by Aboriginal Australians who had become isolated from the rest of the world for over 50,000 years, and not a people who may have preceded them on the continent. Aborigines also have the oldest known oral history in the world, passing through some 300 generations.
So, taking all these discoveries at face value, perhaps a revised record of Out of Africa should appear something like this:
- about 25 million years ago, the family of primates known as the hominoids, or human-like animals, first surfaced in Africa;
- the particular line to which humans belong then diverged from that of the gorillas and chimpanzees between five and seven million years ago – although we still share 98.4 per cent of our genetic make-up with modern chimps;
- roughly 200,000 years ago, modern humans, anatomically indistinguishable from us, emerged in Africa;
- about 120,000 or 130,000 years ago, they hunted and gathered their way out of Africa and on to other parts of the world (Previous suggestion: sometime after 65,000 years ago).
- between 50,000 and 60,000 years ago they had reached and colonised Australia[6] (now revised to approximately 65,000 years);
- by 40,000 years ago, anatomically modern humans had replaced more archaic populations, such as the Neanderthals, our closest extinct human relatives, to become a globally distributed species.
[1] Peter Spinks, “Out of Africa’ theory of human evolution under fire”, SMH, 25 August 2014. The discovery is mentioned in greater detail when considering the fossil finds in China's autonomous region of Guangxi Zhua.
[2] Extract from the research team’s article in the journal Quaternary International, cited in Ibid. The research team was led by anthropologist Christopher Bae of the University of Hawaii.
[3] Ibid.
[4] Attributed to Simon Armitage from Royal Holloway, a University of London college and cited in Ibid.
[5] Ibid.
[5.1] See https://www.dailysabah.com/history/2017/07/20/humans-arrived-in-australia-20000-years-before-europe-study-says; http://www.dailymail.co.uk/sciencetech/article-3153421/The-Australians-Aborigines-DNA-analysis-quashes-claims-unknown-race-preceded-indigenous-people-live-today.html (published 8 July 2015; 25 July 2016). For another article confidently refuting the out-of-Africa “myth”, and the whole idea of a mitochondrial Eve and Y-chromosome Adam originating in Africa, and asserting that, based on DNA evidence, Homo sapiens and the Denisovans all descended from the Australian Aborigine, see Steven Strong “researcher, author and former high school teacher” and Andy Whiteley, “ a former corporate manager turned writer, (and) editor”: https://wakeup-world.com/2013/12/16/dna-evidence-debunks-the-out-of-africa-theory-of-human-evolution/
[6] Hiscock, supra.