Stf made another video and he made some interesting claims two are the most interesting too me.
That if Homo Sapiens went through a ten thousand person bottle head we would have the same genetic problems cheetahs are having. And he claims that since different groups accumulate mutations at different rates the divergence
the claims are made bewteen
29:31 to 36:26
and
1:00:00 to 1:02:55
32:23- 35:05
As usual, heās very confused. He mixes up the out of Africa bottleneck with an entirely different human bottleneck, and for some reason proposes that this bottleneck occurred during the transition from Homo erectus to Homo sapiens.
Iāve no idea where heās getting the idea that if humans went through a sustained bottleneck, we should have diversity comparable to cheetahs. Thatās just such a baseless claim to make. Lots of factors make it difficult to compare our population history with that of cheetahs in any meaningful way.
He canāt even keep his narrative straight. According to him, scientists discovered that humans had low genetic diversity so āinventedā the idea that weād been through bottlenecks as an ad hoc solution, but now heās saying that if we went through a bottleneck weād have much less genetic diversity. If itās an ad hoc explanation, then the magnitude of the bottleneck could be fit to our current level of genetic diversity. So is it ad hoc or not? He canāt have it both ways.
If only we could simulate different scenarios of human population history including bottlenecks and compare it with realityā¦
Iām not sure SFT and reality are on speaking terms.
Yeah that cheetah claim is interesting because it debunks his own point. First of all, its an exception that proves the rule that most species donāt experience extreme bottlenecks. Why are cheetahs and humans the only examples they bring up when 1) humans should have 4 times the diversity (eight people on the ark vs two) and 2) as far as Iām aware, they consider cheetahs to be the same ark kind as all of Felidae? They shouldnāt show any signs of the bottleneck from the ark if cheetahs diverged from other felids well after the bottleneck took place. Lastly, itās a deflection that doesnāt solve his problem of a reduction to 10 alleles max for any gene. Long bottleneck, short bottleneck, it doesnāt matter. 10 alleles.
Also, Iāve been meaning to have this conversation with him. He reeeaaaally doesnāt get how phylogenetics works. A faster mutation rate would create more diversity, but it shouldnāt have an effect on the divergence, barring events that are statistical anomalies or magic.
The ten alleles maximum is an important point. Thatās sets the ceiling, absent intragenic recombination. Which happens, but not fast enough to generate extant diversity in ~4ky. Itās also a ceiling, not a floor; small populations experience strong genetic drift, so the likelihood of losing one of those alleles (and all the SNPs it contains) before recombination breaks those variants up is extremely high.
Exactly. Also, his distinction of long versus short bottlneck just isnāt a thing, as far as Iām aware. Even if the shorter bottleneck did fix something, Noahās offspring have to prolong it by undergoing massive amounts of inbreeding to maintain the correct haplogroups, which lengthens the bottleneck and further reduces available diversity. Each generation would only be allowed to reproduce with siblings for likely hundreds of years. Excuse me if Iām dubious, especially if the mutation rate is supposed to be 50x higher and intragenic recombination is happening multiple times per meiosis
I love how you guys have quickly and immediately picked up and understood the salience of the TRM4A and TMR10A data.
Yes there is a distinction.
There severity of a bottleneck depends on both the length (in generations) and bottleneck population size. A brief bottleneck is less severe.
Technically, it isnāt fast enough to generate extant divergence of genetic alleles.
Ah ok. Thanks for the correction! Although, I think my point still stands because the reduction to 8 individuals is likely worse than a few hundred years with an effective population of a few thousand, but you know the math better than me haha. Also, the YEC model still has to artificially extend that bottleneck to maintain correct haplogroups.
For equal effective population sizes, sure. But the types SFT likes to compare is a 1000 individual bottleneck for āsome numberā of generations against a 1 generation bottleneck to 8 followed by exponential growth. If my math is right, getting from 8 to 1024 would be a 12% reduction in heterozygosity, which would take around 250 generations for a sustained Ne=1000 bottleneck. The Toba bottleneck, if there was such a thing, is only suggested as about 40 generations at not less than Ne=1000, so 3% max for Toba vs 12% for Noah.