Angela
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Consanguinity was certainly common, and to be expected, I would think, given the small population numbers and the isolated nature of the small settlements. Whether it contributed to their extinction is another question.
See:
http://blogs.discovermagazine.com/c...ence-for-neanderthal-inbreeding/#.XHS5QOhKhPZ
"The first strong case of Neanderthal inbreeding came in 2014, when scientists published a genome extracted from a toe bone found in the Altai Mountains of Siberia. Alive roughly 120,000 years ago, this Neanderthal woman had closely related parents: half-siblings, double first cousins, an uncle-niece couple or some other combo with equal relatedness.This conclusion was based on a DNA statistic called runs of homozygosity(ROH)."
"When researchers compared the Altai Neanderthal’s two genomes, there were long segments of practically identical DNA — runs of homozygosity. The abundance of especially long ROH — over 10 centimorgans (cM), a proxy unit for distance along a chromosome — indicates this individual’s parents shared ancestors within two generations. For instance, they could have had the same mother, but different fathers (the half sibling scenario) or shared both sets of grandparents (the double first cousins case). If they shared an ancestor much longer ago — say a great-great-great-great-great grandparent — the ROH would have been broken into shorter segments.
Which was also the case: The researchers additionally counted smaller ROH (between 2.5 and 10 cM), and found the sum surpassed this count for present-day human populations, like the Karitiana of the Brazilian Amazon, known to be small isolated groups with a history of consanguinity. An abundance of short ROH can result from a small population size, past inbreeding or both, so it’s hard to say what’s driving the pattern in the Altai Neanderthal. But given the data available, it’s a fair hypothesis that consanguinity was common in this Neanderthal’s pedigree."
"In 2017 researchers counted ROH in the genome of a roughly 50,000-year-old Neanderthal woman from Vindija, Croatia. This individual did not have abundant long tracts of matching DNA, indicating her parents were not close relatives. However, the quantity of short ROH (2.5 – 10 cM) was on par with the Altai Neanderthal and above present-day groups with a history of isolation and inbreeding."
As for El Sidron,
"Although full genomes aren’t available, portions of their DNA that have been sequenced are consistent with the group being close kin, who may have been too close. A 2011 paper, analyzing mitochondrial DNA (mtDNA) — a small loop of genetic code passed on only by mothers — revealed low diversity within the group. The adult males in particular seem to have been maternal kin. Another study fully sequenced chromosome 21 from one El Sidrón individual and found a similar pattern as in the Vindija Neanderthal: an abundance of short ROH.
Skeletal abnormalities suggesting the El Sidron Neanderthals were inbred (Source: Rios et al 2019 Scientific Reports 9:1697)
And earlier this month, anthropologists reported hard — skeletal — evidence for consanguinity among the El Sidrón Neanderthals. The team identified 17 bones, belonging to at least 4 individuals, showing congenital abnormalities. These are conditions present at birth, as opposed to ones developed during life through injury, infection or nutritional deficiencies. In the El Sidrón remains, the congenital features included cleft or asymmetric vertebrae, a misshapen kneecap and a baby tooth retained into adulthood. The identified conditions are rare in living humans (between 3.8 to 0.00004 percent) and may be harmless, but they do occur more frequently in cases of inbreeding. In other words, these skeletal features suggest the parents were kin."
"Cultural and circumstantial sensitivities aside, at a basic biological level, consanguinity is bad. Let’s remember another a high school bio lesson: Mating between people with very similar genetic makeup — i.e. close kin — increases chances their children will have recessive genetic disorders. These are diseases, like Tay-Sachs or cystic fibrosis, that occur when you inherit two bad copies of a particular gene. If diseased gene variants run in a family, and members of that family are mating, there’s a good chance some children will be born with the condition.
Beyond these cases of potentially fatal diseases, consanguinity also causes so-called inbreeding depression: inbred individuals have reduced evolutionary fitness, or survival and reproductive success. One study compared rates of death before age 10 between the children of first cousins and unrelated parents, considering over 2.14 million people across 15 countries. The analysis found “3.5 percent excess deaths” among first-cousin kids. Across many studies in different populations, consanguinity has been associated with undesirable traits, including low IQ and congenital heart disease."
The lower reproductive success associated with high levels of consanguinity might also explain their small numbers. So, it could have been a vicious loop for them.
See:
http://blogs.discovermagazine.com/c...ence-for-neanderthal-inbreeding/#.XHS5QOhKhPZ
"The first strong case of Neanderthal inbreeding came in 2014, when scientists published a genome extracted from a toe bone found in the Altai Mountains of Siberia. Alive roughly 120,000 years ago, this Neanderthal woman had closely related parents: half-siblings, double first cousins, an uncle-niece couple or some other combo with equal relatedness.This conclusion was based on a DNA statistic called runs of homozygosity(ROH)."
"When researchers compared the Altai Neanderthal’s two genomes, there were long segments of practically identical DNA — runs of homozygosity. The abundance of especially long ROH — over 10 centimorgans (cM), a proxy unit for distance along a chromosome — indicates this individual’s parents shared ancestors within two generations. For instance, they could have had the same mother, but different fathers (the half sibling scenario) or shared both sets of grandparents (the double first cousins case). If they shared an ancestor much longer ago — say a great-great-great-great-great grandparent — the ROH would have been broken into shorter segments.
Which was also the case: The researchers additionally counted smaller ROH (between 2.5 and 10 cM), and found the sum surpassed this count for present-day human populations, like the Karitiana of the Brazilian Amazon, known to be small isolated groups with a history of consanguinity. An abundance of short ROH can result from a small population size, past inbreeding or both, so it’s hard to say what’s driving the pattern in the Altai Neanderthal. But given the data available, it’s a fair hypothesis that consanguinity was common in this Neanderthal’s pedigree."
"In 2017 researchers counted ROH in the genome of a roughly 50,000-year-old Neanderthal woman from Vindija, Croatia. This individual did not have abundant long tracts of matching DNA, indicating her parents were not close relatives. However, the quantity of short ROH (2.5 – 10 cM) was on par with the Altai Neanderthal and above present-day groups with a history of isolation and inbreeding."
As for El Sidron,
"Although full genomes aren’t available, portions of their DNA that have been sequenced are consistent with the group being close kin, who may have been too close. A 2011 paper, analyzing mitochondrial DNA (mtDNA) — a small loop of genetic code passed on only by mothers — revealed low diversity within the group. The adult males in particular seem to have been maternal kin. Another study fully sequenced chromosome 21 from one El Sidrón individual and found a similar pattern as in the Vindija Neanderthal: an abundance of short ROH.
Skeletal abnormalities suggesting the El Sidron Neanderthals were inbred (Source: Rios et al 2019 Scientific Reports 9:1697)
"Cultural and circumstantial sensitivities aside, at a basic biological level, consanguinity is bad. Let’s remember another a high school bio lesson: Mating between people with very similar genetic makeup — i.e. close kin — increases chances their children will have recessive genetic disorders. These are diseases, like Tay-Sachs or cystic fibrosis, that occur when you inherit two bad copies of a particular gene. If diseased gene variants run in a family, and members of that family are mating, there’s a good chance some children will be born with the condition.
Beyond these cases of potentially fatal diseases, consanguinity also causes so-called inbreeding depression: inbred individuals have reduced evolutionary fitness, or survival and reproductive success. One study compared rates of death before age 10 between the children of first cousins and unrelated parents, considering over 2.14 million people across 15 countries. The analysis found “3.5 percent excess deaths” among first-cousin kids. Across many studies in different populations, consanguinity has been associated with undesirable traits, including low IQ and congenital heart disease."
The lower reproductive success associated with high levels of consanguinity might also explain their small numbers. So, it could have been a vicious loop for them.