Greg Cochran, when he was still regularly blogging, would often talk about aging from an evolutionary angle. One perspective he shared was on the relationship between parental (really paternal) aging and genetic load.
After the age of 30 or 35 the number of de novo germline mutations in males starts to increase logarithmically. Older fathers thus pass on more mutations to their offspring than younger fathers. Historically, one of the biggest drivers of high paternal age was polygamy, because it delays and extends male fertility deeper into adulthood. The implication being that populations with long histories of polygamous marriage patterns and high average paternal age (such as much of sub-Saharan Africa and Australian Aborigines) would have significantly higher rates of genetic load.
There's been some other work on generation time differences between populations that also have some bearing on this topic. The following study found an average parental generation time (combining male/female ages) in East Asians, South Asians, and Europeans of around 20 over the past 10,000 generations compared to Africans at almost 27.
The time-depth of these generations intervals implies two things to me: 1.) the ancestors of Eurasians were diverged for a very, very long time from the ancestors of contemporary Africans 2.) likely post-Neolithic differences in marriage patterns between populations aren't the main determinants of paternal age differences between populations (at least not on the macro-level between Africans and Eurasians).
This begs the question of why the ancestors of Eurasians would have had such lower parental ages compared to Africans for so long? And circling back to my initial point about genetic load, a lower long-term generation interval among Eurasians would also have the effect of increasing the accumulation of mutations among the Eurasian population, which would in turn also necessitate higher load accumulation as well, right?
I suspect we don't currently have a good general understanding of the actual phenotypic consequences of the mutation rate differences between populations. I also wonder if our current estimates for population divergences and molecular clock calibration are biased without taking these generation interval variances into account.
For many years here at Wisconsin I was friends with James Crow, and he spent many years working to understand the relationship between mutation rates and paternal age. Culture does have an effect on the average parental age, for some of the reasons you bring up and for others.
One of the biggest effects on generation length is demography. Most theory is looking at equilibrium populations, where population growth is low or negligible over the long term. When populations grow, things are different. Younger parents and especially younger mothers are overrepresented across generations in a growing population. The faster the growth, the more this skews the average generation length.
Of course both African and Eurasian populations have grown a lot in the last 10,000 generations if you look at the continental level. But I expect the details matter. My first guess is that the bottleneck and subsequent dispersal of modern humans across Eurasia probably swamps all other demographic effects on generation length. That was probably 10,000 to 20,000 years of younger parents having a massive impact on all later populations.
Do you think the bottleneck could also distort the divergence estimates as well between Eurasians and Africans? I've seen in various papers (using other methods unrelated to generation lengths) divergences reported as high as 100,000 years, and even longer when comparing against San and other African hunter-gatherers.
The "10-20,000 years of younger parents" would have to be the time immediately following the end of the bottleneck and the corresponding expansion in Eurasia right? Initial Upper Paleolithic beginning around 50,000 years ago, followed by dramatic population increase the following 10-20k years leading to lower generation length? Because I wouldn't expect that the proto-Eurasian population during the bottleneck period itself would have a lower generation interval, since that would seem counter-intuitive based on your second paragraph.
Come to think of it, do we have a proper estimate of when the bottleneck period actually started? 50k years pretty well established for the ending but I don't know that we have strong handle on the start?
These estimates are in fairly rapid flux lately as geneticists using different approaches are finding ways that they are model-dependent. First cut is always a model in which one parameter varies holding all else constant, but of course many parameters actually are poorly estimated and changed over time across populations. At the moment it's looking like bottleneck period was fairly long and started well before 50k, releasing in the range of 45k, with Neanderthal mixture happening in a narrow window around 47k. Probably lower generation time has characterized descendants of that founder group for the entire period since then.
Putin forgot/overlooked that the brain ages and obviously cannot be replaced with new brain having the life experience, person-ness of the original--at least, not yet.
His comment reveals his morality and ego that an individual would choose to maintain their life at the expense of humans, using current science. I immediately thought of Trump choosing to live to 150, getting new organs to maintain himself. It really is, to me, disgusting.
I have to assume that the "open mic" was deliberate in order to drive news of this event. With that in mind, it is fascinating the way that political leaders are using biology in their messaging and disruption of global health.
Greg Cochran, when he was still regularly blogging, would often talk about aging from an evolutionary angle. One perspective he shared was on the relationship between parental (really paternal) aging and genetic load.
After the age of 30 or 35 the number of de novo germline mutations in males starts to increase logarithmically. Older fathers thus pass on more mutations to their offspring than younger fathers. Historically, one of the biggest drivers of high paternal age was polygamy, because it delays and extends male fertility deeper into adulthood. The implication being that populations with long histories of polygamous marriage patterns and high average paternal age (such as much of sub-Saharan Africa and Australian Aborigines) would have significantly higher rates of genetic load.
There's been some other work on generation time differences between populations that also have some bearing on this topic. The following study found an average parental generation time (combining male/female ages) in East Asians, South Asians, and Europeans of around 20 over the past 10,000 generations compared to Africans at almost 27.
https://www.science.org/doi/10.1126/sciadv.abm7047
The time-depth of these generations intervals implies two things to me: 1.) the ancestors of Eurasians were diverged for a very, very long time from the ancestors of contemporary Africans 2.) likely post-Neolithic differences in marriage patterns between populations aren't the main determinants of paternal age differences between populations (at least not on the macro-level between Africans and Eurasians).
This begs the question of why the ancestors of Eurasians would have had such lower parental ages compared to Africans for so long? And circling back to my initial point about genetic load, a lower long-term generation interval among Eurasians would also have the effect of increasing the accumulation of mutations among the Eurasian population, which would in turn also necessitate higher load accumulation as well, right?
I suspect we don't currently have a good general understanding of the actual phenotypic consequences of the mutation rate differences between populations. I also wonder if our current estimates for population divergences and molecular clock calibration are biased without taking these generation interval variances into account.
For many years here at Wisconsin I was friends with James Crow, and he spent many years working to understand the relationship between mutation rates and paternal age. Culture does have an effect on the average parental age, for some of the reasons you bring up and for others.
One of the biggest effects on generation length is demography. Most theory is looking at equilibrium populations, where population growth is low or negligible over the long term. When populations grow, things are different. Younger parents and especially younger mothers are overrepresented across generations in a growing population. The faster the growth, the more this skews the average generation length.
Of course both African and Eurasian populations have grown a lot in the last 10,000 generations if you look at the continental level. But I expect the details matter. My first guess is that the bottleneck and subsequent dispersal of modern humans across Eurasia probably swamps all other demographic effects on generation length. That was probably 10,000 to 20,000 years of younger parents having a massive impact on all later populations.
Do you think the bottleneck could also distort the divergence estimates as well between Eurasians and Africans? I've seen in various papers (using other methods unrelated to generation lengths) divergences reported as high as 100,000 years, and even longer when comparing against San and other African hunter-gatherers.
The "10-20,000 years of younger parents" would have to be the time immediately following the end of the bottleneck and the corresponding expansion in Eurasia right? Initial Upper Paleolithic beginning around 50,000 years ago, followed by dramatic population increase the following 10-20k years leading to lower generation length? Because I wouldn't expect that the proto-Eurasian population during the bottleneck period itself would have a lower generation interval, since that would seem counter-intuitive based on your second paragraph.
Come to think of it, do we have a proper estimate of when the bottleneck period actually started? 50k years pretty well established for the ending but I don't know that we have strong handle on the start?
These estimates are in fairly rapid flux lately as geneticists using different approaches are finding ways that they are model-dependent. First cut is always a model in which one parameter varies holding all else constant, but of course many parameters actually are poorly estimated and changed over time across populations. At the moment it's looking like bottleneck period was fairly long and started well before 50k, releasing in the range of 45k, with Neanderthal mixture happening in a narrow window around 47k. Probably lower generation time has characterized descendants of that founder group for the entire period since then.
Putin forgot/overlooked that the brain ages and obviously cannot be replaced with new brain having the life experience, person-ness of the original--at least, not yet.
His comment reveals his morality and ego that an individual would choose to maintain their life at the expense of humans, using current science. I immediately thought of Trump choosing to live to 150, getting new organs to maintain himself. It really is, to me, disgusting.
I have to assume that the "open mic" was deliberate in order to drive news of this event. With that in mind, it is fascinating the way that political leaders are using biology in their messaging and disruption of global health.