"Let’s also keep in mind how much stronger natural selection was 55,000 years ago. Today, infant mortality is largely gone and we’re making progress in reducing fetal mortality. The gene pool would now take a lot longer to purge itself. "
i bet this is wrong. first, selection can work on reproductive output, not just infant mortality. so if the person is sterile due to load, work is done. but my bigger objection is i suspect that the load of selection and purging is being taken up at the scale of in utero; our species' miscarriage rates are btwn 25-50% from fertilization on.
"We do, however, in the case of the pygmies and the Khoisans, who have been in continual contact with various populations up to the present. Yes, there are ways to remove recent admixture from the calculations, but they are subject to error."
don't understand this objection. the issue is that a complex of admixture might be present in foragers, but we know what their average distance from the agriculturalists is. and, we know the introgression happened pretty recently (order of thousands of years), so it's a clean ingress.
"That estimate, however, is based on the assumption of a single introgression some 55,000 years ago. Many academics argue for multiple introgressions that go farther back in time."
there have been multiple introgressions. but the one that happened 55K BP is the one there's a signal of. the other groups probably went extinct (like the first moderns in europe, who seem to have mixed with neanderthals, but left no modern descendents).
"This kind of methodology is generally superior to one where the effects are estimated through a model where each calculation is plagued by uncertain assumptions and margins of error."
no, you are measuring different things. you say "hybrid incompabilities cause fertility problems." you think the iceland data is better for gauging fertility; it is. but the genomic data is better for gauging hybrid incompatibility baring physiological assessment of offspring since they'll leave a biological is signature there. studying hybrid incompatibility is not a weird/marginal field, it's at the heart of the study of speciation so the methods are well known, well used, and well understood in the broad sketch. you compare outgroup genomic signature in genic vs nongenic, how is this is hard?
"In contrast, we have not yet reconstructed the genomes of the various non-Khoisan groups that have introgressed into the Khoisan gene pool over the past 150,000 years. "
if you are talking about archaics, that should increase the likelihood of purging. i'm alluding to the 150-200K separation of the khoisan.
also, there have been many papers on african whole genomics in the least 10 years. none report the finding you are looking for here, because none see it to my knowledge. i occasionally ask. (mostly they are looking for neanderthal/archaic stuff, but in the process they would be able to see selective purging in places like south africa pretty easily). it's not in the literature because it's a default hypothesis.
"Razib may be referring to the finding that, on average, any two individuals are 99.9% genetically identical – as measured by nucleotide sequences. So what’s left to measure?
"
no, i'm talking ibd measures. 1st cousins is 1/8. 2nd cousins 1/32. and so on. the icelanders are also exceptionally homogeneous for a world population. that's why they were studied early.
as i said i'm not going to talk extensively about this topic anymore, there's nothing to talk about (i respond to peter's questions because some of them seem to be misunderstanding my point or what not). and peter has long has particular professional interests as an anthropologist, it's fine to ask these sorts of questions, though i lost interest a while back when i concluded there's no "there there."
but, i have to say, i like this website, but the main reason i get involved in these arguments it's weird how many of you are so fascinated by this idea that outbreeding is what's leading to a crash in feritlity when i know most of you well enough that you have don't have many children yourself ;) and we have fertility crashing in nations like korea despite massive homogeneity within 2 generations, while admixed israel is going against the grain. it's pretty obviously culture and economics. and i say this as someone who thinks genetics is important.
i'm a pronatalist (3 kids myself). but some of you guys fixating on the race question are just interested in race, which is fine, but just admit that. most of you don't have many children or choose not too :) [remember, i've been engaging with you people for 22 years, i know your kid ;]
"if the person is sterile due to load, work is done."
- Sterility is the most severe form of outbreeding depression. In most cases, outbreeding depression leads only to a reduction in viability of the embryo or fetus.
"i suspect that the load of selection and purging is being taken up at the scale of in utero"
- Today, yes. In the past, no. Infant mortality was almost 50% in hunter-gatherer societies.
In utero mortality is estimated at 30 to 50%. We're now reducing it through greater recourse to premature delivery.
"we know the introgression happened pretty recently (order of thousands of years), so it's a clean ingress."
- In the case of Bantu admixture, we're looking at multiple introgressions over the last 4,000 years, and we cannot assume that the Bantu 4,000 years ago were genetically identical to the Bantu today. Again, the main problem with your methodology is the very high level of noise, in comparison to the genealogical method of the Icelandic and Danish studies.
"the one that happened 55K BP is the one there's a signal of. "
- We cannot make that assumption. The Skhul-Qafzeh hominins were genetically much closer to modern humans than to Neandertals, so any admixture from them would be similar to that later admixture. There is no clean way of telling the two apart.
"the genomic data is better for gauging hybrid incompatibility baring physiological assessment of offspring since they'll leave a biological is signature there."
- The authors of those studies never claim to be measuring all the effects of hybridization, just the most obvious ones. Again, you're looking at the extreme tail end of outbreeding depression. The measurable incompatibilities that we see with Neandertal/modern human hybridization are a tiny fraction of all the incompatibilities that may arise
"if you are talking about archaics, that should increase the likelihood of purging"
- Undoubtedly. But we have not yet sequenced the genomes of those African "Neandertals." I say "genomes" because there were probably several archaic populations in Africa.
"it's not in the literature because it's a default hypothesis."
- It's not in the literature because outbreeding depression is not measurable with that sort of methodology.
"this idea that outbreeding is what's leading to a crash in feritlity"
- I didn't make that claim, and I thought I was clear on that point. With patience and perseverance, most couples can have at least three children. The fertility decline in South Korea is due to other factors, and I agree that Israel is a model to follow for reversing the fertility decline.
You should use capital letters. For literate people, most of the reading process consists of a lot of unconscious guessing about what the words are, how to break up phrases etc. This is why many types of errors go unnoticed as the brain of the quick reader unconsciously fixes them. Anything unusual interferes with this process. Whenever I read your comments, I have to consciously think about where each sentence begins and ends because the full stop on its own without a capital letters doesn't mark it for me intuitively. This is very tedious, especially when the content itself is sufficiently difficult to require concentration. While it may be conventional in elite tech circles to dispense with capital letters, I think the average Substack reader is like me.
This research could indicate outbreeding depression (European/West-African) because the HapK allele, which is very rare in African populations but introduced to African Americans through their European ancestry, leads to increased heart attack risk perhaps due to genetic incompatibility.
I think that this is not too much more than speculation without theory. We ought to be modeling theses concepts in silico and trying to understand the potential interactions.
I think this presents an opportunity! If we want to see if this theory holds, do the math and modeling then test it's predictions againsts a new dataset. If they agree then that is much better evidence of outbreeding than anything at present.
"Let’s also keep in mind how much stronger natural selection was 55,000 years ago. Today, infant mortality is largely gone and we’re making progress in reducing fetal mortality. The gene pool would now take a lot longer to purge itself. "
i bet this is wrong. first, selection can work on reproductive output, not just infant mortality. so if the person is sterile due to load, work is done. but my bigger objection is i suspect that the load of selection and purging is being taken up at the scale of in utero; our species' miscarriage rates are btwn 25-50% from fertilization on.
"We do, however, in the case of the pygmies and the Khoisans, who have been in continual contact with various populations up to the present. Yes, there are ways to remove recent admixture from the calculations, but they are subject to error."
don't understand this objection. the issue is that a complex of admixture might be present in foragers, but we know what their average distance from the agriculturalists is. and, we know the introgression happened pretty recently (order of thousands of years), so it's a clean ingress.
"That estimate, however, is based on the assumption of a single introgression some 55,000 years ago. Many academics argue for multiple introgressions that go farther back in time."
there have been multiple introgressions. but the one that happened 55K BP is the one there's a signal of. the other groups probably went extinct (like the first moderns in europe, who seem to have mixed with neanderthals, but left no modern descendents).
"This kind of methodology is generally superior to one where the effects are estimated through a model where each calculation is plagued by uncertain assumptions and margins of error."
no, you are measuring different things. you say "hybrid incompabilities cause fertility problems." you think the iceland data is better for gauging fertility; it is. but the genomic data is better for gauging hybrid incompatibility baring physiological assessment of offspring since they'll leave a biological is signature there. studying hybrid incompatibility is not a weird/marginal field, it's at the heart of the study of speciation so the methods are well known, well used, and well understood in the broad sketch. you compare outgroup genomic signature in genic vs nongenic, how is this is hard?
"In contrast, we have not yet reconstructed the genomes of the various non-Khoisan groups that have introgressed into the Khoisan gene pool over the past 150,000 years. "
if you are talking about archaics, that should increase the likelihood of purging. i'm alluding to the 150-200K separation of the khoisan.
also, there have been many papers on african whole genomics in the least 10 years. none report the finding you are looking for here, because none see it to my knowledge. i occasionally ask. (mostly they are looking for neanderthal/archaic stuff, but in the process they would be able to see selective purging in places like south africa pretty easily). it's not in the literature because it's a default hypothesis.
"Razib may be referring to the finding that, on average, any two individuals are 99.9% genetically identical – as measured by nucleotide sequences. So what’s left to measure?
"
no, i'm talking ibd measures. 1st cousins is 1/8. 2nd cousins 1/32. and so on. the icelanders are also exceptionally homogeneous for a world population. that's why they were studied early.
as i said i'm not going to talk extensively about this topic anymore, there's nothing to talk about (i respond to peter's questions because some of them seem to be misunderstanding my point or what not). and peter has long has particular professional interests as an anthropologist, it's fine to ask these sorts of questions, though i lost interest a while back when i concluded there's no "there there."
but, i have to say, i like this website, but the main reason i get involved in these arguments it's weird how many of you are so fascinated by this idea that outbreeding is what's leading to a crash in feritlity when i know most of you well enough that you have don't have many children yourself ;) and we have fertility crashing in nations like korea despite massive homogeneity within 2 generations, while admixed israel is going against the grain. it's pretty obviously culture and economics. and i say this as someone who thinks genetics is important.
i'm a pronatalist (3 kids myself). but some of you guys fixating on the race question are just interested in race, which is fine, but just admit that. most of you don't have many children or choose not too :) [remember, i've been engaging with you people for 22 years, i know your kid ;]
Please let me address your criticisms one by one:
"if the person is sterile due to load, work is done."
- Sterility is the most severe form of outbreeding depression. In most cases, outbreeding depression leads only to a reduction in viability of the embryo or fetus.
"i suspect that the load of selection and purging is being taken up at the scale of in utero"
- Today, yes. In the past, no. Infant mortality was almost 50% in hunter-gatherer societies.
https://ourworldindata.org/child-mortality-in-the-past
In utero mortality is estimated at 30 to 50%. We're now reducing it through greater recourse to premature delivery.
"we know the introgression happened pretty recently (order of thousands of years), so it's a clean ingress."
- In the case of Bantu admixture, we're looking at multiple introgressions over the last 4,000 years, and we cannot assume that the Bantu 4,000 years ago were genetically identical to the Bantu today. Again, the main problem with your methodology is the very high level of noise, in comparison to the genealogical method of the Icelandic and Danish studies.
"the one that happened 55K BP is the one there's a signal of. "
- We cannot make that assumption. The Skhul-Qafzeh hominins were genetically much closer to modern humans than to Neandertals, so any admixture from them would be similar to that later admixture. There is no clean way of telling the two apart.
"the genomic data is better for gauging hybrid incompatibility baring physiological assessment of offspring since they'll leave a biological is signature there."
- The authors of those studies never claim to be measuring all the effects of hybridization, just the most obvious ones. Again, you're looking at the extreme tail end of outbreeding depression. The measurable incompatibilities that we see with Neandertal/modern human hybridization are a tiny fraction of all the incompatibilities that may arise
"if you are talking about archaics, that should increase the likelihood of purging"
- Undoubtedly. But we have not yet sequenced the genomes of those African "Neandertals." I say "genomes" because there were probably several archaic populations in Africa.
"it's not in the literature because it's a default hypothesis."
- It's not in the literature because outbreeding depression is not measurable with that sort of methodology.
"this idea that outbreeding is what's leading to a crash in feritlity"
- I didn't make that claim, and I thought I was clear on that point. With patience and perseverance, most couples can have at least three children. The fertility decline in South Korea is due to other factors, and I agree that Israel is a model to follow for reversing the fertility decline.
You should use capital letters. For literate people, most of the reading process consists of a lot of unconscious guessing about what the words are, how to break up phrases etc. This is why many types of errors go unnoticed as the brain of the quick reader unconsciously fixes them. Anything unusual interferes with this process. Whenever I read your comments, I have to consciously think about where each sentence begins and ends because the full stop on its own without a capital letters doesn't mark it for me intuitively. This is very tedious, especially when the content itself is sufficiently difficult to require concentration. While it may be conventional in elite tech circles to dispense with capital letters, I think the average Substack reader is like me.
This research could indicate outbreeding depression (European/West-African) because the HapK allele, which is very rare in African populations but introduced to African Americans through their European ancestry, leads to increased heart attack risk perhaps due to genetic incompatibility.
See: https://pubmed.ncbi.nlm.nih.gov/16282974/
A man at the pub told me …
I think that this is not too much more than speculation without theory. We ought to be modeling theses concepts in silico and trying to understand the potential interactions.
I think this presents an opportunity! If we want to see if this theory holds, do the math and modeling then test it's predictions againsts a new dataset. If they agree then that is much better evidence of outbreeding than anything at present.