This could seem crude, so I will put it as politey as I can.
Can falling fertility be attributed in any degree to a failing sense of obligation among wives to allow continuing conjugal rights to their husbands? In these Icelandic and Danish studies consanguinity seems decisive, but the data is pre-feminism. Maybe (post)modern decline in fertility is due to lack of access along with lack of relatedness.
Given what you've said about there being some mechanism that causes greater attraction to people more closely related to ourselves, it's not hard to imagine that less related people would find less to like (sexually and otherwise) in their spouse once the novelty wears off. It doesn't *have to be* only a matter of failure to conceive, lost pregnancies etc.
Did I write that "some mechanism causes greater attraction to people more closely related to ourselves"? I don't recall writing that, but then I write an awful lot ...
The current fertility decline is happening throughout the world, including very homogeneous societies like South Korea and Quebec. It's happening in line with the disintegration of traditional culture, which supported family formation and childbearing. We're entering a new culture where the value of everything is determined by its market value. And — guess what! — kids have negative market value. They cost a lot to raise and they no longer help out with your family business or your family farm. Then they go to college, where they're taught that you and your ancestors were terrible people. So the ROI doesn't seem very interesting.
<blockquote>"Well, no. The past was mostly rather dull. During the entire span of human existence, our ancestors largely lived among kith and kin who looked and behaved pretty much like they did. Life was indeed defined by “an equilibrium state of organically developing kinship networks.” Yes, those networks were disrupted at various times and places, but those disruptions were the exception, not the rule, and they were seared into human memory precisely because they were exceptional."</blockquote>
You're trying to suggest that these exceptions weren't, well, exceptional. That the exceptions were equivalent to a unit of of one of those equilibrium states that repeated over long periods.
But if we look at for example Australia, the exceptional event is the Anglo-Celtic invasion of Australia and the replacement of or introgression into aboriginal genomes. That outweighs the millennia of the equilibrium state that obtained among Australian aborigines and their kinship networks, which might as well never even happened by comparison.
You could broaden your example to encompass the entire European expansion of the past five centuries. That was an exceptional situation: the differences were considerable between the Europeans and the non-Europeans they replaced in terms of technology, military power, and political organization. For the most part, however, they replaced only hunter-gatherers with low population densities (most of the Americas, Siberia, Australia). They had much less success where the non-Europeans were larger in number. In Africa, they established a lasting presence only in South Africa, and how long will that presence last?
Yes, the past 5 centuries of European expansion have been exceptional. They had a greater impact than any prevailing equilibrium states. The exceptional cases and the equilibrium states aren't really comparable.
The failure of European expansion into Africa, and subsequent African population explosion and increasing migration, is another exceptional and potential exception state that may overwhelm any other equilibrium states.
The emphasis on equilibrium states strikes me as a version of Gould's erroneous punctuated equilibrium idea.
There have been large cohort inbreeding studies which show effects out to 5th cousins for height. If outbreeding depression >> inbreeding depression after third cousin distance, studies like that should show no inbreeding depression at that level of relatedness.
So what is going on with the studies you cited? One possibility is something in the structure of Scandinavian society favors inbreeding (inheritances maybe) and at 3-4 cousins this benefit and inbreeding depression are optimal.
Another idea I've had is that there is a social affinity between related peoples. 3-4 cousins are more likely to be friends and get along well than randomized strangers. Maybe the 3-4 cousin marriages are more likely to be tight knit families, and people from tight knit families help each other more, and also have more desire to start their own family and see a large family as desirable.
Could you please provide a reference to those inbreeding studies?
"3-4 cousins are more likely to be friends." No, I don't think so. Not even in Iceland or Denmark.
I don't follow the rest of your reasoning . How does that explain why embryos are more often nonviable the further you marry out? And why would this effect persist in the offspring of such marriages?
Sorry, read it a while ago when Razib was critiquing your first post, and didn't save it. A quick search is only showing meta-analyses, which you find suspect, right?
- If you run into that study again, please let me know. Actually, any relevant study would do. No, I'm not prejudiced against meta-studies.
- I read the paper you linked to. Nothing about cousins. There is only a statement that a behavior will spread through a social network to a maximum of three degrees of separation.
- I have met only one of my cousins on my father's side (and that took some doing). Most people in modern society don't know their cousins.
"Most people in modern society don't know their cousins."
I've met numerous distant cousins that I wouldn't have known about if we weren't Mormons. We keep extensive genealogical records and I used an app developed by BYU which checks for connections. In my congregation (about 100 people), in an area that is not our ancestral homeland, I had a third cousin, a fourth cousin, and several fifth cousins.
It may be the church brough us together, which would be improbable for others. But given how much genetically similar people tend to cluster in the same 'tracks' in life, as in 'The Son also Rises', I expect its more common than you think.
However, I'm curious. If your thesis is correct humanity needs to start marrying 3rd or 4rth cousins or at least closer to the same. How do you see this as happening, if you consider it near impossible to even meet them? Arranged marriages by 23andme?
Yes, we have some sort of mechanism that causes feelings of attraction to genetically related people, even if they aren't really cousins:
"we emphasize again that we can be sure these pairs of friends are not, in fact, distant cousins because they are strictly unrelated and there is no identity by descent."
I prefer non-coercive to coercive measures. To a large extent, people will tend to procreate within those degrees of consanguinity if we simply let them. Keep in mind that fertility is below replacement throughout the developed world and even in much of the developing world. Increasingly, children are being born within two groups:
1) fertile subcultures like the Mormons, the Amish, the Hassidim and, to a lesser extent, evangelical Protestants and traditionalist Catholics; and
2) infertile couples using assisted reproduction.
Both groups are moving us away from the postmodern idea of procreation as an accidental consequence of "love" (regardless of the stability of the relationship) and back toward the traditional view of procreation as serious business with long-term consequences. Both groups are also more receptive to evolutionary thinking. So, in the long-term, the dysfunctionalities of postmodern reproduction will tend to resolve themselves, if we leave people well enough alone.
I've seen that claim made, but haven't seen any studies to support it.
If outbreeding caused British people to grow taller, wouldn't we see that effect in the 19th century, when large numbers of people left farms and villages to live in industrial towns and cities? In actual fact, the opposite occurred:
"The average height of Americans and Europeans decreased during periods of rapid industrialization, possibly due to rapid population growth and broad decreases in economic status. This has become known as the early-industrial growth puzzle (in the U.S. context the Antebellum Puzzle). In England during the early nineteenth century, the difference between the average height of English upper-class youth (students of Sandhurst Military Academy) and English working-class youth (Marine Society boys) reached 22 cm (8.7 in), the highest that has been observed." https://en.wikipedia.org/wiki/Human_height#19th_century
Mean height increased during the 20th century, and the most likely cause was better nutrition.
"Keep in mind how much stronger natural selection was 55,000 years ago. Today, with infant mortality largely gone and fetal mortality reduced, the gene pool would take much longer to purge itself."
Does this statement contradict your other statement that "evolution is accelerating"?
Genetic evolution accelerated more than a hundred-fold when hunting and gathering gave way to farming, beginning some 10,000 years ago. This wasn't due so much to farming per se as to the new cultural environments that farming made possible: sedentism, development of towns and cities, the emergence of the State, codification of behavior through religion, literacy and numeracy, etc. Humans were now adapting to an ever-wider range of cultural environments.
Since the late 19th century, this coevolution has slowed down and even reversed. The main cause is that economic success is no longer linked to reproductive success. Fertility has especially fallen in middle-class families. In addition, the same period saw large declines in infant mortality.
It is indeed likely that human evolution has accelerated through the past few hundred years, though it is unclear what the outcome of that change might be.
The amount of genetic variation accumulating with each generation is accelerating due to recent (century scale) increased mixing of different communities as ease of travel has increased. Also as medical interventions have increased survival of somewhat deleterious DNA mutations.
Meanwhile the intensity of genetic winowing through cultural selection may also be increasing (especially the factors acting on fecundity), though an argument is made that globally culture is becoming more homogeneous, such that a declining proportion of each generation is reproducing and as such the generations are increasingly selected.
Together these suggest an acceleration of evolution as increased rate of production of genetic variation is acted on by increased intensity of selection from that pool of variation.
I was trying to make the point that there has to be variation for selection to act on and the amount of variation now is more than in the past. This does not change the rate of evolution. But if the intensity of selection is increased then under such conditions evolution would depart from a linear rate (say,accelerate).
When societies increase in scale there are more opportunities for specialist subgroups to emerge, whether these be pin makers or night soil collectors etc and there will be selection for various/many specialists over generalists. This specificity is what I was getting towards with 'intensity of selection' over and above simply the relative propagation of cohorts.
Brachiopods were the example I was taught in the 1970s to explain variable rates of evolution.
In the Paleozoic fossil record there is a relatively unchanging Brachiopod lineage that is adapted to a relatively constant environment that repetitively makes use of accumulating genetic drift by spinning off rapidly evolving (ie speciating) lineages that are adapting to more marginal and less stable environments.
But considering the large reproductive disparities between those who have 0-1 kids to the very religious who may have 10 or more, there certainly are still very strong vectors of "evolution".
Yes, fertility has fallen so low within the non-religious population that a large part of natural increase is now due to fertile subcultures, like the Amish, the Mormons, the Hassidim, and to some extent Protestant Evangelicals and Catholic traditionalists.
Masculinity is being devalued throughout the Western world. There are several causes, which tend to feed on each other, but I wouldn't blame immigration. The modern educational system tends to marginalize boys and normal male behavior, and this anti-male attitude is affecting our notions of "good parenting."
I'm not sure I understand your argument. Joffe was arguing that the sperm count decline is caused by an increase in genetic incompatibilities. These incompatibilities are most evident in complex systems of genes, such as those involved in spermatogenesis or embryogenesis.
Are you thinking that soy boys are more common today because testosterone levels are lower?
This could seem crude, so I will put it as politey as I can.
Can falling fertility be attributed in any degree to a failing sense of obligation among wives to allow continuing conjugal rights to their husbands? In these Icelandic and Danish studies consanguinity seems decisive, but the data is pre-feminism. Maybe (post)modern decline in fertility is due to lack of access along with lack of relatedness.
Given what you've said about there being some mechanism that causes greater attraction to people more closely related to ourselves, it's not hard to imagine that less related people would find less to like (sexually and otherwise) in their spouse once the novelty wears off. It doesn't *have to be* only a matter of failure to conceive, lost pregnancies etc.
Did I write that "some mechanism causes greater attraction to people more closely related to ourselves"? I don't recall writing that, but then I write an awful lot ...
The current fertility decline is happening throughout the world, including very homogeneous societies like South Korea and Quebec. It's happening in line with the disintegration of traditional culture, which supported family formation and childbearing. We're entering a new culture where the value of everything is determined by its market value. And — guess what! — kids have negative market value. They cost a lot to raise and they no longer help out with your family business or your family farm. Then they go to college, where they're taught that you and your ancestors were terrible people. So the ROI doesn't seem very interesting.
<blockquote>"Well, no. The past was mostly rather dull. During the entire span of human existence, our ancestors largely lived among kith and kin who looked and behaved pretty much like they did. Life was indeed defined by “an equilibrium state of organically developing kinship networks.” Yes, those networks were disrupted at various times and places, but those disruptions were the exception, not the rule, and they were seared into human memory precisely because they were exceptional."</blockquote>
You're trying to suggest that these exceptions weren't, well, exceptional. That the exceptions were equivalent to a unit of of one of those equilibrium states that repeated over long periods.
But if we look at for example Australia, the exceptional event is the Anglo-Celtic invasion of Australia and the replacement of or introgression into aboriginal genomes. That outweighs the millennia of the equilibrium state that obtained among Australian aborigines and their kinship networks, which might as well never even happened by comparison.
You could broaden your example to encompass the entire European expansion of the past five centuries. That was an exceptional situation: the differences were considerable between the Europeans and the non-Europeans they replaced in terms of technology, military power, and political organization. For the most part, however, they replaced only hunter-gatherers with low population densities (most of the Americas, Siberia, Australia). They had much less success where the non-Europeans were larger in number. In Africa, they established a lasting presence only in South Africa, and how long will that presence last?
Yes, the past 5 centuries of European expansion have been exceptional. They had a greater impact than any prevailing equilibrium states. The exceptional cases and the equilibrium states aren't really comparable.
The failure of European expansion into Africa, and subsequent African population explosion and increasing migration, is another exceptional and potential exception state that may overwhelm any other equilibrium states.
The emphasis on equilibrium states strikes me as a version of Gould's erroneous punctuated equilibrium idea.
There have been large cohort inbreeding studies which show effects out to 5th cousins for height. If outbreeding depression >> inbreeding depression after third cousin distance, studies like that should show no inbreeding depression at that level of relatedness.
So what is going on with the studies you cited? One possibility is something in the structure of Scandinavian society favors inbreeding (inheritances maybe) and at 3-4 cousins this benefit and inbreeding depression are optimal.
Another idea I've had is that there is a social affinity between related peoples. 3-4 cousins are more likely to be friends and get along well than randomized strangers. Maybe the 3-4 cousin marriages are more likely to be tight knit families, and people from tight knit families help each other more, and also have more desire to start their own family and see a large family as desirable.
Could you please provide a reference to those inbreeding studies?
"3-4 cousins are more likely to be friends." No, I don't think so. Not even in Iceland or Denmark.
I don't follow the rest of your reasoning . How does that explain why embryos are more often nonviable the further you marry out? And why would this effect persist in the offspring of such marriages?
Sorry, read it a while ago when Razib was critiquing your first post, and didn't save it. A quick search is only showing meta-analyses, which you find suspect, right?
3-4 cousins more likely to be friends is from another study, and I was able to find this one with a quick search - https://www.pnas.org/doi/abs/10.1073/pnas.0913149107
- If you run into that study again, please let me know. Actually, any relevant study would do. No, I'm not prejudiced against meta-studies.
- I read the paper you linked to. Nothing about cousins. There is only a statement that a behavior will spread through a social network to a maximum of three degrees of separation.
- I have met only one of my cousins on my father's side (and that took some doing). Most people in modern society don't know their cousins.
"Most people in modern society don't know their cousins."
I've met numerous distant cousins that I wouldn't have known about if we weren't Mormons. We keep extensive genealogical records and I used an app developed by BYU which checks for connections. In my congregation (about 100 people), in an area that is not our ancestral homeland, I had a third cousin, a fourth cousin, and several fifth cousins.
It may be the church brough us together, which would be improbable for others. But given how much genetically similar people tend to cluster in the same 'tracks' in life, as in 'The Son also Rises', I expect its more common than you think.
However, I'm curious. If your thesis is correct humanity needs to start marrying 3rd or 4rth cousins or at least closer to the same. How do you see this as happening, if you consider it near impossible to even meet them? Arranged marriages by 23andme?
I must have sent you the wrong link. It's https://www.pnas.org/doi/full/10.1073/pnas.1400825111
It's genetic similarity that you would expect for 4rth cousins predicts friendship, even though they filtered out actual kin.
Yes, we have some sort of mechanism that causes feelings of attraction to genetically related people, even if they aren't really cousins:
"we emphasize again that we can be sure these pairs of friends are not, in fact, distant cousins because they are strictly unrelated and there is no identity by descent."
I prefer non-coercive to coercive measures. To a large extent, people will tend to procreate within those degrees of consanguinity if we simply let them. Keep in mind that fertility is below replacement throughout the developed world and even in much of the developing world. Increasingly, children are being born within two groups:
1) fertile subcultures like the Mormons, the Amish, the Hassidim and, to a lesser extent, evangelical Protestants and traditionalist Catholics; and
2) infertile couples using assisted reproduction.
Both groups are moving us away from the postmodern idea of procreation as an accidental consequence of "love" (regardless of the stability of the relationship) and back toward the traditional view of procreation as serious business with long-term consequences. Both groups are also more receptive to evolutionary thinking. So, in the long-term, the dysfunctionalities of postmodern reproduction will tend to resolve themselves, if we leave people well enough alone.
Sailer wrote, years ago about people of the British isles growing a few inches due to marrying
people who weren't so closely related. Were archaic humans better off genetically? Like wolves compared to dogs.
I've seen that claim made, but haven't seen any studies to support it.
If outbreeding caused British people to grow taller, wouldn't we see that effect in the 19th century, when large numbers of people left farms and villages to live in industrial towns and cities? In actual fact, the opposite occurred:
"The average height of Americans and Europeans decreased during periods of rapid industrialization, possibly due to rapid population growth and broad decreases in economic status. This has become known as the early-industrial growth puzzle (in the U.S. context the Antebellum Puzzle). In England during the early nineteenth century, the difference between the average height of English upper-class youth (students of Sandhurst Military Academy) and English working-class youth (Marine Society boys) reached 22 cm (8.7 in), the highest that has been observed." https://en.wikipedia.org/wiki/Human_height#19th_century
Mean height increased during the 20th century, and the most likely cause was better nutrition.
You would think people would grow taller. However, I wonder if people aren't like goldfish and grow to fit their environment😉
"Keep in mind how much stronger natural selection was 55,000 years ago. Today, with infant mortality largely gone and fetal mortality reduced, the gene pool would take much longer to purge itself."
Does this statement contradict your other statement that "evolution is accelerating"?
Genetic evolution accelerated more than a hundred-fold when hunting and gathering gave way to farming, beginning some 10,000 years ago. This wasn't due so much to farming per se as to the new cultural environments that farming made possible: sedentism, development of towns and cities, the emergence of the State, codification of behavior through religion, literacy and numeracy, etc. Humans were now adapting to an ever-wider range of cultural environments.
Since the late 19th century, this coevolution has slowed down and even reversed. The main cause is that economic success is no longer linked to reproductive success. Fertility has especially fallen in middle-class families. In addition, the same period saw large declines in infant mortality.
I wrote about much of this in "The Great Decline." https://www.anthro1.net/p/the-great-decline
Thanks. So as I thought, evolution is not accelerating.
It remains to be seen.
It is indeed likely that human evolution has accelerated through the past few hundred years, though it is unclear what the outcome of that change might be.
The amount of genetic variation accumulating with each generation is accelerating due to recent (century scale) increased mixing of different communities as ease of travel has increased. Also as medical interventions have increased survival of somewhat deleterious DNA mutations.
Meanwhile the intensity of genetic winowing through cultural selection may also be increasing (especially the factors acting on fecundity), though an argument is made that globally culture is becoming more homogeneous, such that a declining proportion of each generation is reproducing and as such the generations are increasingly selected.
Together these suggest an acceleration of evolution as increased rate of production of genetic variation is acted on by increased intensity of selection from that pool of variation.
Genetic variation does not produce selection. It is simply the raw material upon which selection can act.
Selection is produced by the natural environment or the cultural environment.
Granted. I didn't express myself clearly.
I was trying to make the point that there has to be variation for selection to act on and the amount of variation now is more than in the past. This does not change the rate of evolution. But if the intensity of selection is increased then under such conditions evolution would depart from a linear rate (say,accelerate).
When societies increase in scale there are more opportunities for specialist subgroups to emerge, whether these be pin makers or night soil collectors etc and there will be selection for various/many specialists over generalists. This specificity is what I was getting towards with 'intensity of selection' over and above simply the relative propagation of cohorts.
Brachiopods were the example I was taught in the 1970s to explain variable rates of evolution.
In the Paleozoic fossil record there is a relatively unchanging Brachiopod lineage that is adapted to a relatively constant environment that repetitively makes use of accumulating genetic drift by spinning off rapidly evolving (ie speciating) lineages that are adapting to more marginal and less stable environments.
But considering the large reproductive disparities between those who have 0-1 kids to the very religious who may have 10 or more, there certainly are still very strong vectors of "evolution".
Yes, fertility has fallen so low within the non-religious population that a large part of natural increase is now due to fertile subcultures, like the Amish, the Mormons, the Hassidim, and to some extent Protestant Evangelicals and Catholic traditionalists.
Evolution is self-correcting, if we give it time.
Masculinity is being devalued throughout the Western world. There are several causes, which tend to feed on each other, but I wouldn't blame immigration. The modern educational system tends to marginalize boys and normal male behavior, and this anti-male attitude is affecting our notions of "good parenting."
I'm not sure I understand your argument. Joffe was arguing that the sperm count decline is caused by an increase in genetic incompatibilities. These incompatibilities are most evident in complex systems of genes, such as those involved in spermatogenesis or embryogenesis.
Are you thinking that soy boys are more common today because testosterone levels are lower?