Inbreeding, allee effects and simple stochasticity maybe led to the Extinction of the Neanderthals.

[Morticia Iunia Bruti]

A new study, why the Neanderthals maybe are extincted.

https://journals.plos.org/plosone/ar...l.pone.0225117

[hellheaven1987]

That does not explain why modern Sapiens have both genes of Neanderthals and Denisovans.

[Common Soldier]

That does not explain why modern Sapiens have both genes of Neanderthals and Denisovans.

If Neanderthals were split into small isolated populations as the paper proposes, the arrival of modernhumans would have encouraged I get feeding of the Neanderthals with rhe nearby modern humans than with the more distant and isolated Neanderthals. It would help explain why Neanderthals interbred with modern humans.

[sumskilz]

A new study, why the Neanderthals maybe are extincted.

https://journals.plos.org/plosone/ar...l.pone.0225117

Well, it wouldn't be the last time relatively low fertility indigenous Europeans were replaced by migrants... I'm of course referring to the Neolithic transition.

Neanderthals were a bunch of degenerates. They suffered from fairly high mutation load. I may have mentioned it before. Their population size was evidently too small for purifying selection to operate effectively.

It would help explain why Neanderthals interbred with modern humans.

I'm not sure that needs any special explanation. It seems it would have been downright inevitable in light of this sort of thing and whatever is going on in Wales.

[hellheaven1987]

If Neanderthals were split into small isolated populations as the paper proposes, the arrival of modernhumans would have encouraged I get feeding of the Neanderthals with rhe nearby modern humans than with the more distant and isolated Neanderthals. It would help explain why Neanderthals interbred with modern humans.

Breeding between Neanderthals and Denisovans also happened, in higher rate comparing with Sapiens actually.

[sumskilz]

It's difficult to estimate how much interbreeding took place because of the nature of the inheritance. In the case of both Neanderthal and Denisovan ancestry in modern humans, the pattern is that of adaptive introgression rather than simple admixture. That is there are specific places on the genome where Neanderthal and/or Denisovan genes are very common in particular populations, whereas as we never find them in other places on the genome. For example, the Denisovan version of the EPAS1 gene which regulates production hemoglobin is very common in Tibetans because it enables engaging in more strenuous activity at high altitude. In contrast, the Neanderthal version of the FOXP2 gene associated with language production has never been found in a modern human, presumably because it was selected against.

The fact that there are great deserts in the modern human genome where no archaic introgression exists suggests that those genes didn't work as well for our ancestors, likely because our species had better versions or at least versions that worked better for us. The latter point is important, because it could be that certain genes were well-adapted for our sister species but didn't work as well for us due to compatibility issues. There is no discreet point at which we can objectively say speciation has taken place. Clearly viable offspring could still be produced, but there are many species that can hybrid to produce viable offspring (at least some of the time).

So returning to my initial point. If we see a particular modern human population with 3% average Neanderthal genetic ancestry, we shouldn't infer that this means said population has 3% Neanderthal genealogical ancestry because it could be that the genes were acquired from a very small number of hybrid individuals, since the allele frequencies of this type of ancestry appear to largely (or completely) be the result of positive selection.

[Cyclops]

So there are some positive Denisovian genetic inheritance? I suppose there might also be positive Neanderthal inheritance as well. I'm getting a mental picture of "Frost Humans" (+2 STR) and "Mountain Humans" (+2 END) as sub races in our ancient past. I suppose smaller population size reinforced topospecific adaptions. I feel glad we didn't evolve a blind cave variant.

I don't think Polynesians lineages have been separate from other human families to be a "sub race" or whatever the correct term is but I believe the average height and weight of individuals in Tonga and Samoa etc is significantly higher, suggesting a move toward island gigantism.

The negative effects of inbreeding are obvious even to a casual like myself. In the state of Tasmania there's an horrendous rate of inherited genetic disease, because of low inward migration after foundation. There's a big swathe of Huntington's disease carriers (trace to a single ancestor-its a weird case because with Late onset HD there's actually higher fertility among carriers than non-carriers) and other genetic disorders.

Here's a lovely news story spinning the inbreeding as an asset: https://www.abc.net.au/health/featur...03/1836338.htm

The degree of inbreeding may be reflected in Tasmania's high rates of child sex offences, lower rates of gender balance in positions of power etc. Its a backward place.

The stereotype is of "two-headed yokels haha" but when you got there its shocking. There are a large number of people walking the streets with tiny heads. Last time I was there the population seemed to fall into three categories: 1/3 'normal looking" (could be Nepalese taxi drivers, Anglo receptionists etc but typically not born in Tasmania) 1/2 pinheads (ranging from normal seeming otherwise to barely functional) and 1/6 towering drooling shamblers. There are are a lot of non-standard looking jaws, eyes a bit crooked or the wrong distance apart, its disturbing. Thank goodness they fixed the iodine problem, it used to be goitre central as well.

[Morifea]

Good to know that there is a place even Australians see as backward...
Thats some weird stuff about Tasmania, have some rep for sharing.

Maybe we should help them and add our DNA to their Genepool... provided there are hot Women

[Morticia Iunia Bruti]

Hmmm, problematic because Australia's hottest woman...

Spoiler Alert, click show to read: 

is a Draq.^^

[Morifea]

.... okay, I got it, just avoid this whole continent

[Cyclops]

"That's not a wife".

I have friends from Tasmania and they are nice people. They produce good footballers too (most importantly). However they are ugly:



The one on the left (Jack) has simultaneously a huge chin and yet somehow no chin either. The one on the right (Nick) has a size 5 face on a size 10 head. its not normal, but in Tassie it is.

Both are hardworking skilled players, the younger one (Jack) has turned himself into a matchwinning champion even better than Nick. FWIW Tasmanian players have a reputation for being simple and direct, not subtle or smart.

They have a sister/cousin who died from a horrible genetic disease and the two fellas organise charity games for fundraising. Aplastic anaemia is a rotten disease, and like so many over-represented in Tasmania.

Its actually hard to dig up the stats for it though. There are the usual myths (don't Google "Black Bobs", half the stories are fake and the real ones are horrible enough) and defensive debunking articles "its not that bad". However Mrs Cyclops works in health, as do some of my Tasmanian friends and believe me its a problem. As bad as it is its actually quite under-reported because of the very conservative social attitudes there.

Its quite easy to imagine small groups of Neanderthals specced for ice getting isolated in mountain "islands" of cold climate and inbreeding themselves out of existence. Cultural attitudes (including broader human as well as specific Neanderthal ideas) could exacerbate this problem as well.

Is the Denisovian high altitude adaption thought to be a group characteristic or just a lucky individual mutation?

[hellheaven1987]

Is the Denisovian high altitude adaption thought to be a group characteristic or just a lucky individual mutation?

Probably a lucky few; Polynesians share most genetic similarity with Denisovian today and it seems they had none. In fact I remember reading a report in 2015 suggesting ancient Tibetans did not have EPAS1 until 5th Century.

[sumskilz]

So there are some positive Denisovian genetic inheritance? I suppose there might also be positive Neanderthal inheritance as well.

Most likely all Denisovan and Neanderthal ancestry in modern humans is adaptive. Whether it is positive or not still depends on context. For example, 50% of Native Americans have an increased chance of developing Type 2 diabetes due to Neanderthal genetic inheritance. While I don’t believe the mechanism is fully understood, the issue is no doubt related to some metabolic advantage in their ancestral environment that becomes a liability with a modern diet. If you happen to be a person with more energy in the evening and constantly feel like staying up late even though you’ve got work in the morning, you can thank your Neanderthal ancestry for that. During northern latitude winters, it was an advantage to not always feel sleepy whenever it was dark out. A lot of Neanderthal genes in modern humans code for hair and skin structure and pigmentation, which is obviously advantageous or disadvantageous depending on environment.

I don't think Polynesians lineages have been separate from other human families to be a "sub race" or whatever the correct term is but I believe the average height and weight of individuals in Tonga and Samoa etc is significantly higher, suggesting a move toward island gigantism.

They also have more efficient fat storage, which was a life saving advantage on long voyages across the Pacific, but is a problem for people eating a modern diet.

Is the Denisovian high altitude adaption thought to be a group characteristic or just a lucky individual mutation?

We only have one near complete Denisovan genome, three fragmentary Denisovan genomes, and a genome from a girl who was half Neanderthal and half Denisovan. All are from the same cave.

Probably a lucky few; Polynesians share most genetic similarity with Denisovian today and it seems they had none. In fact I remember reading a report in 2015 suggesting ancient Tibetans did not have EPAS1 until 5th Century.

Everybody has EPAS1. The Denisovan/Tibetan version you're referring to is a variant. It could easily have been a typical Denisovan genotype, at least in regions where it was particularly useful. There is evidence of the variant having undergone a positive selection sweep in Tibetans over something like the past 3,000 to 5,000 years. This is an inference from modern genomes that doesn’t mean that it wasn’t common in people living in the region before that. I’d say it’s more likely that it means that most of the ancestry of modern Tibetans is from people who migrated into the region from about that time, and that the frequency has been steadily increasing since then. The variant is very old, and yet it hasn’t spread much to people who don’t live at high altitude even though it also seems to convey some athletic advantage. This suggests that it is actually selected against in other environments, so there must be some tradeoff (at least in our species). That alone could explain why Polynesians don’t have it even if it was common in Denisovans.

A couple of recent related papers:

The genome of the offspring of a Neanderthal mother and a Denisovan father

Multiple Deeply Divergent Denisovan Ancestries in Papuans

[Cyclops]

...

We only have one near complete Denisovan genome, three fragmentary Denisovan genomes, and a genome from a girl who was half Neanderthal and half Denisovan. All are from the same cave....

So quite enough then for absolute certainty .

The discussion about selection for environments and unexpected side effects like diabetes makes me wonder about a whole range of ailments. I have a nephew on the autism spectrum, and his focus is laser like: maybe its a characteristic selected for in very specific circumstances.

My neighbours have a profoundly disabled child, requiring 24 hour care. They are strong intelligent healthy individuals who both happen to carry the recessive gene for this horrible condition: they'd be great partners for any prospective match up, maybe the same recessive gene has positive expressions? I seem to recall a Mediterranean group with a resistance to many viruses (or was it cancer?) but a predisposition to aenemia.

The Neanderthal/Denisovian cross plays to your sex-addict caveman trope. What's next, Eohippus centaurs?

[athanaric]

The stuff about Tasmania makes me wonder if the aboriginal population didn't suffer from the same issues, being even smaller than the current population.

[Cyclops]

The stuff about Tasmania makes me wonder if the aboriginal population didn't suffer from the same issues, being even smaller than the current population.

Its quite possible. Aboriginal societies were often characterised by complex social requirements and taboos, which may have served in part to ensure healthy exogamy (as well as stablising fertility and harmonising social relations). For example in the Northern Territory I recall one custom was a married man could not look at his wife's mother, and had to speak to her in a different language to his other relations. There were very intricate moiety systems for sorting potential mates, that seem to serve the cause of genetic health.

We don't have a lot of records of Tasmanian customs though as the British settlement was made as a penal colony, and preceded by sealers and whalers who introduced diseases (that along with enslavement and once farming was established, outright massacres) wiped out the society and left only tattered remnants down to this day.

All remaining Tasmanian Aborigines (and the definitions are disputed) share European DNA as well so there may be problems trying to find evidence on the genetic side. However we have evidence of a largish (at least twenty thousand people) island population with a hunter-gatherer economy, sharing with the mainland fire management practices. The stone tool debate is politically charged (in the past Tasmanian Aborigines were characterised as "so backward they could not even make fire and had to wait for lightning strikes", an obvious furphy) but it looks like the last big wave of technologies from Asia (including specific tool types relating to grass cutting and cultivation, as well as dingoes) did not reach Tasmania.

Its a hard subject to discuss. Because of past prejudice and outrageous racism there's been a soft touch on counterclaims such as "the British colony was a Nazi Death factory for massacring Aborigines". Many farmers cheerfully massacred Aborigines but its true disease played a big part too and it was never official government policy to wipe all black people out: they however did little to stop massacres or punish whites who did murder blacks. The motif of "a dying race forgotten by time" made it very easy to treat aborigines as already dead.

So its unlikely you'd find a reasonable treatise on the subject. Tasmania was isolated from mainland Australia about ten thousand years ago, and isolated populations on the Bass Strait Islands died out because they lacked sea going craft and were "too small" so there is definitely a floor on a viable population size.