Did early humans nearly go extinct some 900,000 years ago?

[rogue06]

New research indicates that humanity may have been on the brink of extinction between 813,000 and 930,000 years ago, being reduced to just about 1300 reproducing individuals. Geneticists suggest that this bottleneck could have led to increased inbreeding and a subsequent loss in human genetic diversity that has persisted to this day. Whatever caused this drastic reduction must have had long-term effects since the population didn't really start expanding again for roughly another 117,000 years.

Such a sharp drop in population could explain why fossils from this time have been scarce.

The time in question, known as the middle Pleistocene transition (MPT), did experience massive climate shifts, but that started a good deal before the sudden drop in the human population (approximately 1.25 mya).

Nick Ashton, a Paleolithic archaeologist at the British Museum's Department of Britain, Europe and Prehistory, and who is not involved with the study, suggests that any population crash only impacted a limited group, perhaps in Africa, who may have been the ancestors of modern humans, while not much affecting other groups of humans who aren't our ancestors.

Those affected were Homo heidelbergensis, considered to be the most recent common ancestor for both modern humans and Neanderthals.

Source: Human ancestors nearly went extinct 900,000 years ago

A new technique analysing modern genetic data suggests that pre-humans survived in a group of only 1,280 individuals.

Human ancestors in Africa were pushed to the brink of extinction around 900,000 years ago, a study shows. The work¹, published in Science, suggests a drastic reduction in the population of our ancestors well before our species, Homo sapiens, emerged. The population of breeding individuals was reduced to just 1,280 and didn’t expand again for another 117,000 years.

“About 98.7% of human ancestors were lost,” says Haipeng Li, a population geneticist at the University of Chinese Academy of Sciences in Beijing, who co-led the study. He says that the fossil record in Africa and Eurasia between 950,000 and 650,000 years ago is patchy and that “the discovery of this bottleneck may explain the chronological gap”.

Nick Ashton, an archaeologist at the British Museum in London, who wrote a related perspective², says he was intrigued by the tiny size of the population. “This would imply that it occupied a very localized area with good social cohesion for it to survive,” he says. “Of greater surprise is the estimated length of time that this small group survived. If this is correct, then one imagines that it would require a stable environment with sufficient resources and few stresses to the system.”

Clues from modern DNA

To make their discovery, the researchers needed to invent new tools. Advances in genome sequencing have improved scientists’ understanding of population sizes for the period after modern humans emerged, but the researchers developed a methodology that enabled them to fill in details about earlier human ancestors. Serena Tucci, an anthropologist at Yale University in New Haven, Connecticut, says that such work was sorely needed. “We still know very little about the population dynamics of early human ancestors for several reasons, including methodological limitations and difficulties in obtaining ancient DNA data from old Homo specimens,” she says.

The researchers’ method allowed them to reconstruct ancient population dynamics on the basis of genetic data from present-day humans. By constructing a complex family tree of genes, the team was able to examine the finer branches of the tree with greater precision, identifying significant evolutionary events.

The technique “put the spotlight on the period 800,000 to one million years ago — for which there is much unknown — in a way that hasn’t been done before,” says Stanley Ambrose, an anthropologist at the University of Illinois at Urbana-Champaign.

This period was part of the Early-Middle Pleistocene transition — a time of drastic climate change, when glacial cycles became longer and more intense. In Africa, this led to long periods of drought. Li says that the changing climate might have wiped out human ancestors and forced new human species to emerge. Eventually, these might have evolved into the last common ancestor of modern humans and our extinct relatives, the Denisovans and Neanderthals.

Around 813,000 years ago, the population of pre-humans began to swell again. How our ancestors managed to survive, and what allowed them to flourish once more, remains unclear, says Ziqian Hao, a population geneticist at the Shandong First Medical University and Shandong Academy of Medical Sciences in Jinan, and a co-author of the paper. However, he says that the bottleneck is likely to have had a crucial impact on human genetic diversity, driving many important features of modern humans, such as brain size. He estimates that up to two-thirds of genetic diversity was lost. “It represents a key period of time during the evolution of humans. So there are many important questions to be answered,” he says.

Ashton would like to see the researchers’ findings backed by more archaeological and fossil evidence. The authors “suggest that the bottleneck was a global crash in population”, he says, “but the number of archaeological sites outside Africa suggests that this is not the case. A regional bottleneck might be more likely.”


[b]Source[/b

© Copyright Original Source

The paper is Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition, with the summary and abstract from it posted below:

Editor’s summary

Today, there are more than 8 billion human beings on the planet. We dominate Earth’s landscapes, and our activities are driving large numbers of other species to extinction. Had a researcher looked at the world sometime between 800,000 and 900,000 years ago, however, the picture would have been quite different. Hu et al. used a newly developed coalescent model to predict past human population sizes from more than 3000 present-day human genomes (see the Perspective by Ashton and Stringer). The model detected a reduction in the population size of our ancestors from about 100,000 to about 1000 individuals, which persisted for about 100,000 years. The decline appears to have coincided with both major climate change and subsequent speciation events. —Sacha Vignieri

Abstract

Population size history is essential for studying human evolution. However, ancient population size history during the Pleistocene is notoriously difficult to unravel. In this study, we developed a fast infinitesimal time coalescent process (FitCoal) to circumvent this difficulty and calculated the composite likelihood for present-day human genomic sequences of 3154 individuals. Results showed that human ancestors went through a severe population bottleneck with about 1280 breeding individuals between around 930,000 and 813,000 years ago. The bottleneck lasted for about 117,000 years and brought human ancestors close to extinction. This bottleneck is congruent with a substantial chronological gap in the available African and Eurasian fossil record. Our results provide new insights into our ancestry and suggest a coincident speciation event.

[Sparko]

This was the great war where the Elves, Orcs, and Hobbits went extinct, leaving only Humans and Dwarves.

[rogue06]

This was the great war where the Elves, Orcs, and Hobbits went extinct, leaving only Humans and Dwarves.

Though some of the ogres survived and hid out in the mountains until recently when one descended upon Washington D.C.

[shunyadragon]

New research indicates that humanity may have been on the brink of extinction between 813,000 and 930,000 years ago, being reduced to just about 1300 reproducing individuals. Geneticists suggest that this bottleneck could have led to increased inbreeding and a subsequent loss in human genetic diversity that has persisted to this day. Whatever caused this drastic reduction must have had long-term effects since the population didn't really start expanding again for roughly another 117,000 years.

Such a sharp drop in population could explain why fossils from this time have been scarce.

The time in question, known as the middle Pleistocene transition (MPT), did experience massive climate shifts, but that started a good deal before the sudden drop in the human population (approximately 1.25 mya).

Nick Ashton, a Paleolithic archaeologist at the British Museum's Department of Britain, Europe and Prehistory, and who is not involved with the study, suggests that any population crash only impacted a limited group, perhaps in Africa, who may have been the ancestors of modern humans, while not much affecting other groups of humans who aren't our ancestors.

Those affected were Homo heidelbergensis, considered to be the most recent common ancestor for both modern humans and Neanderthals.

Source: Human ancestors nearly went extinct 900,000 years ago

A new technique analysing modern genetic data suggests that pre-humans survived in a group of only 1,280 individuals.

Human ancestors in Africa were pushed to the brink of extinction around 900,000 years ago, a study shows. The work¹, published in Science, suggests a drastic reduction in the population of our ancestors well before our species, Homo sapiens, emerged. The population of breeding individuals was reduced to just 1,280 and didn’t expand again for another 117,000 years.

“About 98.7% of human ancestors were lost,” says Haipeng Li, a population geneticist at the University of Chinese Academy of Sciences in Beijing, who co-led the study. He says that the fossil record in Africa and Eurasia between 950,000 and 650,000 years ago is patchy and that “the discovery of this bottleneck may explain the chronological gap”.

Nick Ashton, an archaeologist at the British Museum in London, who wrote a related perspective², says he was intrigued by the tiny size of the population. “This would imply that it occupied a very localized area with good social cohesion for it to survive,” he says. “Of greater surprise is the estimated length of time that this small group survived. If this is correct, then one imagines that it would require a stable environment with sufficient resources and few stresses to the system.”

Clues from modern DNA

To make their discovery, the researchers needed to invent new tools. Advances in genome sequencing have improved scientists’ understanding of population sizes for the period after modern humans emerged, but the researchers developed a methodology that enabled them to fill in details about earlier human ancestors. Serena Tucci, an anthropologist at Yale University in New Haven, Connecticut, says that such work was sorely needed. “We still know very little about the population dynamics of early human ancestors for several reasons, including methodological limitations and difficulties in obtaining ancient DNA data from old Homo specimens,” she says.

The researchers’ method allowed them to reconstruct ancient population dynamics on the basis of genetic data from present-day humans. By constructing a complex family tree of genes, the team was able to examine the finer branches of the tree with greater precision, identifying significant evolutionary events.

The technique “put the spotlight on the period 800,000 to one million years ago — for which there is much unknown — in a way that hasn’t been done before,” says Stanley Ambrose, an anthropologist at the University of Illinois at Urbana-Champaign.

This period was part of the Early-Middle Pleistocene transition — a time of drastic climate change, when glacial cycles became longer and more intense. In Africa, this led to long periods of drought. Li says that the changing climate might have wiped out human ancestors and forced new human species to emerge. Eventually, these might have evolved into the last common ancestor of modern humans and our extinct relatives, the Denisovans and Neanderthals.

Around 813,000 years ago, the population of pre-humans began to swell again. How our ancestors managed to survive, and what allowed them to flourish once more, remains unclear, says Ziqian Hao, a population geneticist at the Shandong First Medical University and Shandong Academy of Medical Sciences in Jinan, and a co-author of the paper. However, he says that the bottleneck is likely to have had a crucial impact on human genetic diversity, driving many important features of modern humans, such as brain size. He estimates that up to two-thirds of genetic diversity was lost. “It represents a key period of time during the evolution of humans. So there are many important questions to be answered,” he says.

Ashton would like to see the researchers’ findings backed by more archaeological and fossil evidence. The authors “suggest that the bottleneck was a global crash in population”, he says, “but the number of archaeological sites outside Africa suggests that this is not the case. A regional bottleneck might be more likely.”


[b]Source[/b

© Copyright Original Source

The paper is Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition, with the summary and abstract from it posted below:

Editor’s summary

Today, there are more than 8 billion human beings on the planet. We dominate Earth’s landscapes, and our activities are driving large numbers of other species to extinction. Had a researcher looked at the world sometime between 800,000 and 900,000 years ago, however, the picture would have been quite different. Hu et al. used a newly developed coalescent model to predict past human population sizes from more than 3000 present-day human genomes (see the Perspective by Ashton and Stringer). The model detected a reduction in the population size of our ancestors from about 100,000 to about 1000 individuals, which persisted for about 100,000 years. The decline appears to have coincided with both major climate change and subsequent speciation events. —Sacha Vignieri

Abstract

Population size history is essential for studying human evolution. However, ancient population size history during the Pleistocene is notoriously difficult to unravel. In this study, we developed a fast infinitesimal time coalescent process (FitCoal) to circumvent this difficulty and calculated the composite likelihood for present-day human genomic sequences of 3154 individuals. Results showed that human ancestors went through a severe population bottleneck with about 1280 breeding individuals between around 930,000 and 813,000 years ago. The bottleneck lasted for about 117,000 years and brought human ancestors close to extinction. This bottleneck is congruent with a substantial chronological gap in the available African and Eurasian fossil record. Our results provide new insights into our ancestry and suggest a coincident speciation event.

Good reference but I do not consider it news. I await further research on better estimates as to where and how many humans survived. I believe previous research determined that an early population of human ancestors survived in Southwest Africa.

[shunyadragon]

There is a considerable gray area of our African ancestry at the time of the genetic bottleneck ~900,000 ago including between closely related specieciew Home naledi, Homo heidelbergensis, and others. Both may have been fairly wide spread across Africa at the time of the bottleneck event.

Source: https://en.wikipedia.org/wiki/Homo_naledi

Homo naledi is an extinct hominin species discovered in 2013 in the Rising Star Cave, Cradle of Humankind, South Africa dating to the Middle Pleistocene 335,000–236,000 years ago. The initial discovery comprises 1,550 specimens of bone, representing 737 different skeletal elements, and at least 15 different individuals. Despite this exceptionally high number of specimens, their classification with other Homo species remains unclear.

Along with similarities to contemporary Homo, they share several characteristics with the ancestral Australopithecus as well as early Homo (mosaic evolution), most notably a small cranial capacity of 465–610 cm³ (28.4–37.2 cu in), compared with 1,270–1,330 cm³ (78–81 cu in) in modern humans. They are estimated to have averaged 143.6 cm (4 ft 9 in) in height and 39.7 kg (88 lb) in weight, yielding a small encephalization quotient of 4.5. H. naledi brain anatomy seems to have been similar to contemporary Homo, which could indicate comparable cognitive complexity. The persistence of small-brained humans for so long in the midst of bigger-brained contemporaries revises the previous conception that a larger brain would necessarily lead to an evolutionary advantage, and their mosaic anatomy greatly expands the known range of variation for the genus.

H. naledi anatomy indicates that, though they were capable of long-distance travel with a humanlike stride and gait, they were more arboreal than other Homo, better adapted to climbing and suspensory behaviour in trees than endurance running. Tooth anatomy suggests consumption of gritty foods covered in particulates such as dust or dirt. Though they have not been associated with stone tools or any indication of material culture, they appear to have been dextrous enough to produce and handle tools, and therefore may have manufactured Early or Middle Stone Age industries since no other human species in the vicinity at that time has been discovered. It has also been controversially postulated that these individuals were given funerary rites, and were carried into and placed in the chamber.
Discovery[edit]

A map of the Rising Star Cave, marking the Dinaledi Chamber in yellow and the Lesedi Chamber in red
On 13 September 2013 while exploring the Rising Star Cave system in the Cradle of Humankind, South Africa, cavers Rick Hunter and Steven Tucker found hominin fossils at the bottom of the Dinaledi Chamber.^[2] On the 24th, they returned to the chamber and took photos, which they showed to South African palaeoanthropologists Pedro Boshoff and Lee Rogers Berger on October 1.^[2] Berger assembled an excavation team which included Hunter and Tucker, the so-called "Underground Astronauts".^[3]

The chamber had been entered at least once before, by cavers in the early 1990s. They rearranged some bones and may have caused further damage, although much of the floor in the chamber had not been walked on prior to 2013.^[4] It lies about 80 m (260 ft) from the main entrance, at the bottom of a 12 m (39 ft) vertical drop, and the 10 m (33 ft) long main passage is only 25–50 cm (10 in – 1 ft 8 in) at its narrowest.^[4] In total, more than 1,550 pieces of bone belonging to at least fifteen individuals (9 immature and 6 adults)^[5] have been recovered from the clay-rich sediments. Berger and colleagues published the findings in 2015.^[6]

The fossils represent 737 anatomical elements – including portions of the skull, jaw, ribs, teeth, limbs, and inner ear bones – from old, adult, young, and infantile individuals. There are also some articulated or near-articulated elements, including the skull with the jaw bone, and nearly complete hands and feet.^[6][4] With the number of individuals of both sexes across several age demographics, it is the richest assemblage of associated fossil hominins discovered in Africa. Aside from the Sima de los Huesos collection and later Neanderthal and modern human samples, the excavation site has the most comprehensive representation of skeletal elements across the lifespan, and from multiple individuals, in the hominin fossil record.^[6]

The holotype specimen, DH1, comprises a male partial calvaria (top of the skull), partial maxilla, and nearly complete jawbone. The paratypes, DH2 through DH5, all comprise partial calvaria. Berger and colleagues named the species Homo naledi in 2015, the specific name meaning "star" in the Sotho language, because the remains came from Rising Star Cave.^[6]

The remains of at least three additional individuals (two adults and a child) were reported in the Lesedi Chamber of the cave by John Hawks and colleagues in 2017.^[7]
Classification[edit]


In 2017, the Dinaledi remains were dated to 335,000–236,000 years ago in the Middle Pleistocene, using electron spin resonance (ESR) and uranium–thorium (U-Th) dating on three teeth, and U-Th and paleomagnetic dating of the sediments they were deposited in.^[1] The fossils were previously thought to have dated to 1–2 million years ago^[6][8][9][3] because no similarly small-brained hominins had previously been known from such a recent date in Africa.^[10] The smaller-brained Homo floresiensis of Indonesia lived on an isolated island, and apparently became extinct shortly after the arrival of modern humans.^[11]

The ability of such a small-brained hominin to have survived for so long in the midst of bigger-brained Homo greatly revises previous conceptions of human evolution and the notion that a larger brain would necessarily lead to an evolutionary advantage.^[10] Their mosaic anatomy also greatly expands the range of variation for the genus.^[12]

H. naledi is hypothesised to have branched off very early from contemporaneous Homo. It is unclear whether they branched off at around the time of H. habilis, H. rudolfensis, and A. sediba; are a sister taxon to H. erectus and the contemporaneous large-brained Homo; or are a sister taxon to the descendants of H. heidelbergensis (modern humans and Neanderthals). This would mean that they branched off from contemporary Homo at latest before 900,000 years ago, and possibly as early as the Pliocene. It is also possible their ancestors speciated after an interbreeding event between Homo and late australopithecines.^[10] Looking at the skull, H. naledi has the closest affinities to H. erectus.^[12]

© Copyright Original Source