300,000-YEAR-OLD MODERN HUMAN FOSSILS FOUND IN MOROCCO: WOW!
Our concept of human origins was thrown for a major loop in 2017 with the announcement of the discovery of modern human fossils, dated to 300,00 years ago, about 100,000 years older than any other known remains of our species, Homo sapien, in an old mine on a desolate mountain in Morocco. Both the date of the fossils — skulls, limb bones and teeth from at least five individuals — and their location were surprises — “a blockbuster discovery.” [Source: Will Dunham, Reuters, June 8, 2017 ^]
Will Dunham of Reuters wrote: “The antiquity of the fossils was startling - a “big wow,” as one of the researchers called it. But their discovery in North Africa, not East or even sub-Saharan Africa, also defied expectations. And the skulls, with faces and teeth matching people today but with archaic and elongated braincases, showed our brain needed more time to evolve its current form. “This material represents the very root of our species,” said paleoanthropologist Jean-Jacques Hublin of Germany’s Max Planck Institute for Evolutionary Anthropology, who helped lead the research published in the journal Nature.
“Before the discovery at the site called Jebel Irhoud, located between Marrakech and Morocco’s Atlantic coast, the oldest Homo sapiens fossils were known from an Ethiopian site called Omo Kibish, dated to 195,000 years ago. “The message we would like to convey is that our species is much older than we thought and that it did not emerge in an Adamic way in a small ‘Garden of Eden’ somewhere in East Africa. It is a pan-African process and more complex scenario than what has been envisioned so far,” Hublin said. ^
“The Moroccan fossils, found in what was a cave setting, represented three adults, one adolescent and one child roughly age 8, thought to have lived a hunter-gatherer lifestyle. These were found alongside bones of animals including gazelles and zebras that they hunted, stone tools perhaps used as spearheads and knives, and evidence of extensive fire use. An analysis of stone flints heated up in the ancient fires let the scientists calculate the age of the adjacent human fossils, Max Planck Institute archaeologist Shannon McPherron said. ^
Websites and Resources on Hominins and Human Origins: Smithsonian Human Origins Program humanorigins.si.edu ; Institute of Human Origins iho.asu.edu ; Becoming Human University of Arizona site becominghuman.org ; Talk Origins Index talkorigins.org/origins ; Last updated 2006. Hall of Human Origins American Museum of Natural History amnh.org/exhibitions ; Wikipedia article on Human Evolution Wikipedia ; Evolution of Modern Humans anthro.palomar.edu ; Human Evolution Images evolution-textbook.org; Hominin Species talkorigins.org ; Paleoanthropology Links talkorigins.org ; Britannica Human Evolution britannica.com ; Human Evolution handprint.com ; National Geographic Map of Human Migrations genographic.nationalgeographic.com ; Humin Origins Washington State University wsu.edu/gened/learn-modules ; University of California Museum of Anthropology ucmp.berkeley.edu; BBC The evolution of man" bbc.co.uk/sn/prehistoric_life; "Bones, Stones and Genes: The Origin of Modern Humans" (Video lecture series). Howard Hughes Medical Institute.; Human Evolution Timeline ArchaeologyInfo.com ; Walking with Cavemen (BBC) bbc.co.uk/sn/prehistoric_life ; PBS Evolution: Humans pbs.org/wgbh/evolution/humans; PBS: Human Evolution Library www.pbs.org/wgbh/evolution/library; Human Evolution: you try it, from PBS pbs.org/wgbh/aso/tryit/evolution; John Hawks' Anthropology Weblog johnhawks.net/ ; New Scientist: Human Evolution newscientist.com/article-topic/human-evolution;
Websites and Resources on Neanderthals: Wikipedia: Neanderthals Wikipedia ; Neanderthals Study Guide thoughtco.com ; Neandertals on Trial, from PBS pbs.org/wgbh/nova; The Neanderthal Museum neanderthal.de/en/ ; The Neanderthal Flute, by Bob Fink greenwych.ca. Websites and Resources on Prehistoric Art: Chauvet Cave Paintings archeologie.culture.fr/chauvet ; Cave of Lascaux archeologie.culture.fr/lascaux/en; Trust for African Rock Art (TARA) africanrockart.org; Bradshaw Foundation bradshawfoundation.com; Australian and Asian Palaeoanthropology, by Peter Brown peterbrown-palaeoanthropology.net. Fossil Sites and Organizations: The Paleoanthropology Society paleoanthro.org; Institute of Human Origins (Don Johanson's organization) iho.asu.edu/; The Leakey Foundation leakeyfoundation.org; The Stone Age Institute stoneageinstitute.org; The Bradshaw Foundation bradshawfoundation.com ; Turkana Basin Institute turkanabasin.org; Koobi Fora Research Project kfrp.com; Maropeng Cradle of Humankind, South Africa maropeng.co.za ; Blombus Cave Project web.archive.org/web; Journals: Journal of Human Evolution journals.elsevier.com/; American Journal of Physical Anthropology onlinelibrary.wiley.com; Evolutionary Anthropology onlinelibrary.wiley.com; Comptes Rendus Palevol journals.elsevier.com/ ; PaleoAnthropology paleoanthro.org.
Jebel Irhoud and Its 300,000-Year-Old Modern Human Fossils
The fossils were found at Jebel Irhoud, a former barite mine 100 kilometers west of Marrakesh, where excavations had been going on for years. Ian Sample wrote in The Guardian: “Jebel Irhoud has thrown up puzzles for scientists since fossilised bones were first found at the site in the 1960s. Remains found in 1961 and 1962, and stone tools recovered with them, were attributed to Neanderthals and at first considered to be only 40,000 years old. [Source: Ian Sample, The Guardian, June 7, 2017 |=|]
Gemma Tarlach wrote in Discover: “In 2004, when researchers revisited the previously excavated early hominin site of Jebel Irhoud at first. The mid-20th century mining operations that had turned up the first hominin bones had also destroyed much of the site, and the method in which some of those first finds had been collected made dating them with any confidence a difficult undertaking. But Jebel Irhoud was not finished sharing its secrets. The researchers found an area of the site that had been preserved, and discovered more fossils — from at least five individuals — plus numerous stone tools and other artifacts, some of which appeared to have been heated in a controlled fire. While the bones may get all the headlines, these bits of flint, apparently flaked off into the fire as tools were sharpened, are just as important: The material was perfect for dating using the thermoluminescence method. [Source: Gemma Tarlach, Discover, June 7, 2017]
Sample wrote:“In fresh excavations at the Jebel Irhoud site, Hublin and others found more remains, including a partial skull, a jawbone, teeth and limb bones belonging to three adults, a juvenile, and a child aged about eight years old. The remains, which resemble modern humans more than any other species, were recovered from the base of an old limestone cave that had its roof smashed in during mining operations at the site. Alongside the bones, researchers found sharpened flint tools, a good number of gazelle bones, and lumps of charcoal, perhaps left over from fires that warmed those who once lived there. It’s rather a desolate landscape, but on the horizon you have the Atlas mountains with snow on top and it’s very beautiful,” said Hublin. “When we found the skull and mandible I was emotional. They are only fossils, but they have been human beings and very quickly you make a connection with these people who lived and died here 300,000 years ago.”
Gemma Tarlach wrote in Discover: “While Jebel Irhoud today is surrounded by desert, about 300,000 years ago it would have been more hospitable to hominins and their prey, said Shannon McPherron, lead author of today’s paper dating the fossils and artifacts. When the hominins lived, the layer of the quarried hill in which their fossils were found would have been a cave providing shelter from the elements. Within that same area of the site were the bones of gazelles, zebra, wildebeest and the antelope-like hartebeest. Paleoclimate data points to the area being more humid than today, while the animal bones found suggest, said McPherron, “a landscape that is mainly open, with clumps of trees.” [Source: Gemma Tarlach, Discover, June 7, 2017]
“The overall picture one gets is of a hunting encampment, as they were moving across the area in search of subsistence,” McPherron added. And there is strong evidence the hominins were indeed on the move. The flint they were using for their tools is not local. Analysis showed it came from a site more than 20 kilometers away, suggesting the hominins intentionally sought out quality tool-making material and carried it with them.
Jebel Irhoud People
Will Dunham of Reuters wrote: ““The Jebel Irhoud people had large braincases that lacked the globular shape of those today. Max Planck Institute paleoanthropologist Philipp Gunz said the findings indicate the shape of the face was established early in the history of Homo sapiens, but brain shape, and perhaps brain function, evolved later. But given their modern-looking face and teeth, Hublin said, these people may have blended in today if they simply wore a hat. Hublin did not hazard a guess as to how long ago the very first members of our species appeared, but said it could not have been more than 650,000 years ago, when the evolutionary lineage that led to Homo sapiens split from the one that led to the Neanderthals.” [Source: Will Dunham, Reuters, June 8, 2017]
Ian Sample wrote in The Guardian: “In the first of two papers published in Nature on the researchers describe how they compared the freshly-excavated fossils with those of modern humans, Neanderthals and ancient human relatives that lived up to 1.8 million years ago. Facially, the closest match was with modern humans. The lower jaw was similar to modern Homo sapiens too, but much larger. The most striking difference was the shape of the braincase which was more elongated than that of humans today. It suggests, said Hublin, that the modern brain evolved in Homo sapiens and was not inherited from a predecessor. [Source: Ian Sample, The Guardian, June 7, 2017 |=|]
“Apart from being more stout and muscular, the adults at Jebel Irhoud looked similar to people alive today. “The face of the specimen we found is the face of someone you could meet on the tube in London,” Hublin said. In a second paper, the scientists lay out how they dated the stone tools to between 280,000 and 350,000 years, and a lone tooth to 290,000 years old.
“The remains of more individuals may yet be found at the site. But precisely what they were doing there is unclear. Analysis of the flint tools shows that the stones came not from the local area, but from a region 50 kilometers south of Jebel Irhoud. “Why did they come here? They brought their toolkit with them and they exhausted it,” Hublin said. “The tools they brought with them have been resharpened, resharpened, and resharpened again. They did not produce new tools on the spot. It might be that they did not stay that long, or maybe it was an area they would come to do something specific. We think they were hunting gazelles, there are a lot of gazelle bones, and they were making a lot of fires.”
Faces, Skulls and Brains of Jebel Irhoud People
Despite its modern facial structure, the Jebel Irhoud hominin’s braincase was more primitive, suggesting that the shape of the brain, and possibly cognitive ability, continued to evolve in Homo sapiens after the species was established. Gemma Tarlach wrote in Discover: “The newly described Jebel Irhoud hominins — at least three adults, one adolescent and a child the researchers believe was about 8 years old at time of death — have an intriguing mix of traits. Their faces were essentially ours: “It’s the face of people you could cross in the street today,” says Hublin of the best preserved Jebel Irhoud partial skull. While some of the fossils had larger brow ridges, their facial feature measurements fall within the range of modern humans. [Source: Gemma Tarlach, Discover, June 7, 2017 ^]
“Seen in profile, however, a key difference is apparent: although it had a volume “in the range of modern humans,” according to Hublin, the Jebel Irhoud hominin braincase was lower and more elongated. Based on preserved features of the braincase (the part of the skull that encases, yep, the brain), the researchers believe the Moroccan hominins had a smaller cerebellum than modern humans, though not as small as that of Neanderthals. The cerebellum has been linked to fine motor skills as well as creativity. ^
“Finding early Homo sapiens with modern faces and teeth but more primitive braincases refines our understanding of the actual process of human evolution. “The story of our species in the last 300,000 years is the story of our brain’s evolution,” said Hublin, who added that mutations likely built up over that period, changing the brain’s functional abilities along with its shape and giving the species cognitive advantages in everything from creating better technology to managing social complexities.” ^
Did Modern Humans Live All Over Africa, 300,000 Years Ago?
Will Dunham of Reuters wrote: “There is broad agreement among scientists that Homo sapiens originated in Africa. These findings suggest a complex evolutionary history probably involving the entire continent, with Homo sapiens by 300,000 years ago dispersed all over Africa. Morocco was an unexpected place for such old fossils considering the location of other early human remains. Based on the shape and age of the Moroccan fossils, the researchers concluded that a mysterious, previously discovered 260,000-year-old partial cranium from Florisbad, South Africa also represented Homo sapiens. [Source: Will Dunham, Reuters, June 8, 2017]
Ian Sample wrote in The Guardian: “Hublin said the extreme age of the bones makes them the oldest known specimens of modern humans and poses a major challenge to the idea that the earliest members of our species evolved in a “Garden of Eden” in East Africa one hundred thousand years later. “This gives us a completely different picture of the evolution of our species. It goes much further back in time, but also the very process of evolution is different to what we thought,” Hublin told the Guardian. “It looks like our species was already present probably all over Africa by 300,000 years ago. If there was a Garden of Eden, it might have been the size of the continent.” [Source: Ian Sample, The Guardian, June 7, 2017 |=|]
“Scientists have long looked to East Africa as the birthplace of modern humans. Until the latest findings from Jebel Irhoud, the oldest known remnants of our species were found at Omo Kibish in Ethiopia and dated to 195,000 years old. Other fossils and genetic evidence all point to an African origin for modern humans. Hublin concedes that scientists have too few fossils to know whether modern humans had spread to the four corners of Africa 300,000 years ago. The speculation is based on what the scientists see as similar features in a 260,000-year-old skull found in Florisbad in South Africa. But he finds the theory compelling. “The idea is that early Homo sapiens dispersed around the continent and elements of human modernity appeared in different places, and so different parts of Africa contributed to the emergence of what we call modern humans today,” he said. |=|
“Lee Berger, whose team recently discovered the 300,000 year-old Homo naledi, an archaic-looking human relative, near the Cradle of Humankind World Heritage site outside Johannesburg, said dating the Jebel Irhoud bones was thrilling, but is unconvinced that modern humans lived all over Africa so long ago. “They’ve taken two data points and not drawn a line between them, but a giant map of Africa,” he said. |=|
Tools and Insights from Jebel Irhoud Man
Gemma Tarlach wrote in Discover: “In addition to the hominin fossils, Jebel Irhoud is home to a number of stone tools, many made from non-local material which suggests a higher degree of intention than more primitive hominin tool-makers. “The thing that characterizes the Middle Stone Age from the time that came before is a shift from large, heavy-duty tools to an emphasis on producing lighter stone flakes that allowed increased efficiency in hunting. Along with an emphasis on pointed forms, there was an emphasis on quality materials,” McPherron explained, adding that the hominins’ apparent ease of using controlled fire also speaks to their fairly advanced cognitive abilities for the time.” [Source: Gemma Tarlach, Discover, June 7, 2017]
Ian Sample wrote in The Guardian: “John McNabb, an archaeologist at the University of Southampton, said: “One of the big questions about the emergence of anatomically modern humans has been did our body plan evolve quickly or slowly. This find seems to suggest the latter. It seems our faces became modern long before our skulls took on the shape they have today. There are some intriguing possibilities here too.The tools the people at Jebel Irhoud were making were based on a knapping technique called Levallois, a sophisticated way of shaping stone tools. The date of 300,000 years ago adds to a growing realisation that Levallois originates a lot earlier than we thought. Is Jebel Irhoud telling us that this new technology is linked to the emergence of the hominin line that will lead to modern humans? Does the new find imply there was more than one hominin lineage in Africa at this time? It really stirs the pot.” [Source: Ian Sample, The Guardian, June 7, 2017 |=|]
“Jessica Thompson, an anthropologist at Emory University in Atlanta, said the new results show just how incredible the Jebel Irhoud site is. “These fossils are the rarest of the rare because the human fossil record from this time period in Africa is so poorly represented. They give us a direct look at what early members of our species looked like, as well as their behaviour. “You might also look twice at the brow ridges if you saw them on a living person. It might not be a face you’d see every day, but you would definitely recognise it as human,” she said. “It really does look like in Africa especially, but also globally, our evolution was characterized by numerous different species all living at the same time and possibly even in the same places.” |=|
Cautions About Jebel Irhoud Man
Ian Sample wrote in The Guardian: “John Shea, an archaeologist at Stony Brook University in New York who was not involved in the study, said he was cautious whenever researchers claimed they had found the oldest of anything. “It’s best not to judge by the big splash they make when they are first announced, but rather to wait and see some years down the line whether the waves from that splash have altered the shoreline,” he said, adding that stone tools can move around in cave sediments and settle in layers of a different age. [Source: Ian Sample, The Guardian, June 7, 2017 |=|]
“Shea was also uneasy with the scientists combining fossils from different individuals, and comparing reconstructions of complete skulls from fragmentary remains. “Such ‘chimeras’ can look very different from the individuals on which they are based,” he said.“For me, claiming these remains are Homo sapiens stretches the meaning of that term a bit,” Shea added. “These humans who lived between 50,000-300,000 years ago are a morphologically diverse bunch. Whenever we find more than a couple of them from the same deposits, such as at Omo Kibish and Herto in Ethiopia or Skhul and Qafzeh in Israel, their morphology is all over the place both within and between samples.” |=|
2000-Year-Old African DNA Suggests Humans Evolved At Least 350,000 Years Ago
Josh Davis wrote in IFL Science: “The genetics of a young child who died over 2,000 years ago in what is now South Africa is helping change our understanding of human evolution. The results show that some modern human groups within Africa split at least 260,000 to 350,000 years ago, meaning that our own species has to have evolved at some point before then. [Source: Josh Davis, IFL Science, September 29, 2017 /+]
“This challenges the established timeline of our species, based on fossil evidence, which has for a long time said that Homo sapiens evolved at some point around 200,000 years ago in East Africa. It also suggests that if humans did live in southern Africa around 300,000 years ago, they were likely living alongside other hominins that are also known to have been in the region, such as the famous Homo naledi discovered a few years ago. /+\
“This latest genetic research, published in Science, has only been possible by the incredible advancements seen in recent years in the ability to extract DNA from bones found in warmer and more humid environments. This is now enabling researchers to study the fossils of hominins found in regions of Africa that until now it was thought impossible for genetic material to survive in.
“The team sequenced the genomes from seven individuals, all of which were from Southern Africa, with three dating to between 2,300 and 1,800 years ago, and four who lived around 500 to 300 years ago. They found that while the DNA of the younger remains showed evidence of admixture between different human populations, the genetics of a young boy who died some 2,000 years ago did not, and showed that his last common ancestor with other African groups was around 300,000 years ago. /+\
“The team involved in that work suggested that it seemed more and more likely that there was no single place in which humans first evolved, but that our species cropped up in multiple regions then each population mingled with each other, something that the scientists from this new study concur with.“Thus, both palaeo-anthropological and genetic evidence increasingly points to multiregional origins of anatomically modern humans in Africa,” explained Carina Schlebusch. “I.e. Homo sapiens did not originate in one place in Africa, but might have evolved from older forms in several places on the continent with gene flow between groups from different places.”“ /+\
Neanderthals, Modern Human and Denisovan Divergence
Modern humans, or Homo sapiens, are not the descendants of Neanderthals or Denisovans, although they did live as contemporaries at one time and interbred. It remains unclear when modern humans, Neanderthals and Denisovans diverged from one another. The researchers currently estimate modern humans split from the common ancestors of all Neanderthals and Denisovans between 550,000 and 765,000 years ago, and Neanderthals and Denisovans diverged from each other between 381,000 and 473,000 years ago.
Genetic analysis revealed the parents of the woman whose toe bone they analyzed were closely related — possibly half-siblings, or an uncle and niece, or an aunt and nephew, or a grandfather and granddaughter, or a grandmother and grandson. Inbreeding among close relatives was apparently common among the woman's recent ancestors. It remains uncertain as to whether inbreeding was some kind of cultural practice among these Neanderthals or whether it was unavoidable due to how few Neanderthals apparently lived in this area, said Kay Prüfer, a computational geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
By comparing modern human, Neanderthal and Denisovan genomes, the researchers identified more than 31,000 genetic changes that distinguish modern humans from Neanderthals and Denisovans. These changes may be linked with the survival and success of modern humans — a number have to do with brain development.
"If one speculates that we modern humans carry some genetic changes that enabled us to develop technology to the degree we did and settle in nearly all habitable areas on the planet, then these must be among those changes," Prüfer said. "It is hard to say what exactly these changes do, if anything, and it will take the next few years to find out whether hidden among all these changes are some that helped us modern humans to develop sophisticated technology and settle all over the planet."
Neanderthals and Humans Split 550,000 and 765,000 Years Ago
In 2016, a team lead by Matthias Meyer,a molecular biologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, sequenced 430,000-year-old DNA from a cave in northern Spain, and has pushed back estimates of the time at which the ancient predecessors of humans split from those of Neanderthals to 550,000 and 765,000 years ago. [Source: Ewen Callaway, Nature, March 14, 2016 ]
Ewen Callaway wrote in Nature: “The analysis addresses confusion over which species the remains belong to. A report published in 2013 sequenced a femur’s mitochondrial genome — which is made up of DNA from the cell’s energy-producing structures that is more abundant in cells than is nuclear DNA. It suggested that at least one individual identified from the remains was more closely related to a group called Denisovans — known from remains found thousands of kilometres away in Siberia — than it was to European Neanderthals. “It’s wonderful news to have mitochondrial and nuclear DNA from something that is 430,000 years old. It’s like science fiction. It’s an amazing opportunity,” says Maria Martinón-Torres, a palaeoanthropologist at University College London.
“The remains are known as the Sima hominins because they were found in Sima de los Huesos (Spanish for ‘pit of bones’), a 13-metre-deep shaft in Spain’s Atapuerca mountains. Few ancient sites are as important or intriguing as Sima, which holds the remains of at least 28 individuals, along with those of dozens of cave bears and other animals. The hominins might have plummeted to their death, but some researchers think they were deliberately buried there.
“The Sima hominin skulls have the beginnings of a prominent brow ridge, as well as other traits typical of Neanderthals. But other features, and uncertainties around their age — some studies put them at 600,000 years old, others closer to 400,000 — convinced many researchers that they might instead belong to an older species known as Homo heidelbergensis. Confusion peaked when Meyer, his colleague Svante Pääbo and their team revealed the mitochondrial connection to the Denisovans. But they hoped that retrieving the skeletons’ nuclear DNA — which represents many more lines of ancestry than does mitochondrial DNA, which is inherited solely from the maternal line — would clear things up.”
The nuclear DNA, Meyer’s team,” reported in the March 14, 2016 issue of Nature, “shows that the Sima hominins are in fact early Neanderthals. And its age suggests that the early predecessors of humans diverged from those of Neanderthals between 550,000 and 765,000 years ago — too far back for the common ancestors of both to have been Homo heidelbergensis, as some had posited. Researchers should now be looking for a population that lived around 700,000 to 900,000 years ago, says Martinón-Torres. She thinks that Homo antecessor, known from 900,000-year-old remains from Spain, is the strongest candidate for the common ancestor, if such specimens can be found in Africa or the Middle East.”
Oldest Known Human Fossil Outside Africa Discovered in Israel
African Mitochondrial descent Hannah Devlin wrote in The Guardian: “A human upper jawbone fossil with several teeth and stone tools, dated to between 177,000 and 194,000 years old, were found in a cave in Israel, meaning that modern humans left Africa far earlier than previously thought, prompting scientists to rethink theories about earllu human migration. The fossil is almost twice as old as any previous Homo sapiens remains discovered outside Africa. [Source: Hannah Devlin, The Guardian, January 25, 2018 |=|]
“The fossil, a well-preserved upper jawbone with eight teeth, was discovered at the Misliya cave, which appears to have been occupied for lengthy periods. The teeth are larger than average for a modern human, but their shape and the fossil’s facial anatomy are distinctly Homo sapiens, an analysis of the fossil in the journal Science concludes. |=|
“Sophisticated stone tools and blades discovered nearby suggest the cave’s inhabitants were capable hunters, who used sling projectiles and elegantly carved blades used to kill and butcher gazelles, oryx, wild boars, hares, turtles and ostrich. The team also discovered evidence of matting made from plants that may have been used to sleep on. Radioactive dating places the fossil and tools at between 177,000 and 194,000 years old. “Hershkovitz said the record now indicates that humans probably ventured beyond the African continent whenever the climate allowed it. “I don’t believe there was one big exodus out of Africa,” he said. “I think that throughout hundreds of thousands of years [humans] were coming in and out of Africa all the time.” |=|
“Reconstructions of the ancient climate records, based on deep sea cores, show that the Middle East switched between being humid and extremely arid, and that the region would have been lush and readily habitable for several periods matching the age of the Misliya fossil.” |=|
Early Modern Human, Genetic Studies and Mitochondrial DNA
The human genome, is 99.9 percent identical throughout the world. By looking for DNA difference in the form of mutations and markers (the same mutation found among different people), scientists have been able glean information about where our ancient ancestors came from and how we are related to them.
Genetic studies of ancestry are based on observations of mitochondrial DNA, which is found outside the egg’s nucleus and thus combine with the genome as DNA in the egg does. Unlike chromosomal DNA, which changes when sperm and an egg fuse, mitochondrial DNA is passed on only by the mother, unchanged and unaltered, except for occasional mutations, which occur every several thousand years or so and provide distinctive markers from which common ancestry can be traced. The more differences there are between samples, the longer ago they diverged. In this way mitochondrial DNA not only tells us how similar or dissimilar two people are but also indicates how far one must go back to find a common ancestor.
By the same token most of the Y chromosomes, which determine maleness, are passed on intact from father to son. By comparing mitochondrial DNA and Y chromosomes of people from various populations, geneticists can get a rough idea of where and when groups diverged from one another in the great migrations around the world.
Some scholars warn about making too much of the study of mitochondrial DNA because patterns can be interpreted in different ways and there is no way to check for sure if they are valid or not.
Scientists believe that all in modern 21st century human beings descended from Eve, a hypothetical female believed to have lived somewhere in Africa around 150,000 years ago, who carried a particular type of mitochondrial DNA passed on only to female. Scientists determined this by measuring the range of variation in the DNA of different populations.
The Eve Theory was introduced in 1987 in the famous "mitochondrial Eve" article by the late Allan Wilson of the University of California, Berkeley. The theory is based on fact that mitochondrial DNA contains genetic information that is only passed down from mothers to their children and variations in population over time can be studied by examining harmless mutations passed from one generation to the next.
Wilson and his research team studied the mitochondrial DNA of women around the world and found that women of African descent have twice as much genetic diversity as non-African women. Since key mutations occurred at a steady rate, it was reasoned modern humans must have lived in Africa twice as long as anywhere else. Eve clearly was not the only woman that lived at that time but she contained genes that were passed on in an unbroken chain of mothers to the present day.
The theory has credibility not because there was only a single individual, Eve, but because the genetic lineage of all other Eves has become extinct in way the at the surnames disappear among family that have no children or only daughters. There have been several studies that have challenged the “Eve” theory. One study found much greater DNA diversity than is suggested by the Eve Theory.
According to genetic evidence the human population was reduced to around 2,000 individuals around 70,000 years ago.
Image Sources: Wikimedia Commons, Nature, phys.org and Natural History magazine
Text Sources: National Geographic, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Nature, Scientific American. Live Science, Discover magazine, Discovery NewsNatural History magazine, Archaeology magazine, The New Yorker, Time, BBC, The Guardian, Reuters, AP, AFP and various books and other publications.
Last updated September 2018