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Human generation times across the past 250,000 years

Richard J. Wang, Samer I. Al-Saffar, Jeffrey Rogers, Matthew W. Hahn

2023 · Science Advances

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From the abstract

The generation times of our recent ancestors can tell us about both the biology and social organization of prehistoric humans, placing human evolution on an absolute time scale. We present a method for predicting historical male and female generation times based on changes in the mutation spectrum. Our analyses of whole-genome data reveal an average generation time of 26.9 years across the past 250,000 years, with fathers consistently older (30.7 years) than mothers (23.2 years). Shifts in sex-averaged generation times have been driven primarily by changes to the age of paternity, although we report a substantial increase in female generation times in the recent past. We also find a large difference in generation times among populations, reaching back to a time when all humans occupied Africa.

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owenversteeg
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Alright, to the core argument here: you say if we all ate a diet of potatoes, bread, corn, milk, etc we would all die young of a heart attack and be obese. I say the opposite, which is that modern processed foods are what is giving us heart attacks and making us obese. So, about the article we're all commenting on. Pollan wrote this in 2007, and I quote: >Don’t eat anything your great-great-grandmother wouldn’t recognize as food. (Sorry, but at this point Moms are as confused as the rest of us, which is why we have to go back a couple of generations, to a time before the advent of modern food products.) Generation length varies significantly across human history,…
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geographical location, population groups etc. but the average across the last quarter million years is twenty seven years [5]. The average American is 39 (Pollan was 52 when he wrote this) so let's say roughly speaking we're looking at 39+(4*27) =147 so 2007-147=1860. In the 1860s life expectancy at birth was about 36 and life expectancy at age 15 was about 60. So we're talking roughly the mid-late 1800s to early 1900s. In other words, before the modern use (and quantity) of vegetable oils, food processed on a large scale, most preservatives, modern food advertising, packaging, foods designed for texture, et cetera. These things only started in the early 1900s, but it took time for production to increase, around WW2 - and by the 1960s the average Eastern European was consuming about 6kg of mass-produced vegetable oil a year. Not enough to make everyone obese, but enough to show up as a blip on a chart. Does it? Yes. The heaviest segments of society were already increasing in weight at this time [0]. In the 1960s, texture science and research on the appearance of food started to take off [3] - and yes, even in the USSR this was something people paid attention to. Packaging was now intentionally designed to stimulate appetites. Stabilizers, colorants and flavorings were in use, even in many poorer countries. By the 1970s, soda was in full swing. There were local sodas (Baikal in the USSR, Kofola in Czechoslovakia) but even Pepsi entered the Soviet market in 1971, and it was immediately popular, despite its high price. Now you can see obesity becoming a problem societally; in 1975 it was considered an issue and measured nearly worldwide for the first time [4]. Defending my claim that "obesity rates back then were near zero" is a bit tricky because it was so rare it wasn't considered a societal problem in the early 1900s. But we do have some data points. For example, the heaviest 1% of 18-26yo men in Denmark had a BMI of 28 in 1939 [0], and this did not cross 30 (obese) until 1951. The heaviest 5% of 18-26yo men had a BMI of under 25 in 1939; today, the Danish national average is 25.3. As for heart issues, in 1900 there were 137.4 deaths of heart disease per 100k, vs 192.9 deaths per 100k in 2010. That is despite the fact that 92 million US adults are on statins, which often have serious side effects. Personal anecdotes unfortunately don't hold up to the data, which is crystal clear: in the year 1900, when we ate a pre-modern diet, rates of obesity were near-zero and deaths from heart disease were significantly fewer. But, like you said, what if someone ate that farmers' diet today? Turns out the Amish have significantly lower rates of obesity than their neighbors. Must be the physical exercise, not the diet, no? Well... the US military is quite physically active compared to your average person, and yet 70% are overweight or obese. [0] https://www.science.org/doi/10.1126/sciadv.adg6237 [1] see e.x. Romania, Yugoslavia https://ourworldindata.org/grapher/vegetable-oil-production?... [2] https://www.nejm.org/doi/full/10.1056/NEJMp1113569 [3] https://doi.org/10.1080/20549547.2017.1355720 [4] https://ourworldindata.org/obesity [5] https://doi.org/10.1126/sciadv.abm7047
JumpCrisscross
Neutral mention · rule
> bit difficult to arrive at any number of years past 10,000 for any invention imaginable The mean time between paradigm shifts in the natural sciences [1] is 25 years. (Max: 144 years, between Copernican cosmology and Vesalius's work on anatomy in 1543 and the transition to classical mechanics in 1687. Exempting that, the mean time is 18 years.) I would take that, which is remarkably close to to the length of a generation [2], as being a fundamental factor of the maximum extent of our technological forecasting abilities. A century, 4x that factor, strikes me as the upper bound, though I could be convinced of even 10x in a very stable field. 400x, on the other hand, seems absurd. [1] https://en.wikipedia.org/wiki/Paradigm_shift#Natural_science... ranges taken at midpoint [2] https://www.science.org/doi/10.1126/sciadv.abm7047
mighmi
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Historically, having your first child around 27 was average except for the wealthy. The post war period was a historical aberration of young marriage. > fathers consistently older (30.7 years) than mothers (23.2 years) https://www.science.org/doi/10.1126/sciadv.abm7047
waterhouse
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Can you point to the text that addresses this? The closest thing I see in the article is this paragraph: Children's DNA inherited from their parents contains roughly 25 to 75 new mutations, which allows scientists to compare the parents and offspring, and then to classify the kind of mutation that occurred. When looking at mutations in thousands of children, IU researchers noticed a pattern: The kinds of mutations that children get depend on the ages of the mother and the father. Later: Hahn, Wang and their co-authors built a model that uses de novo mutations—a genetic alteration that is present for the first time in one family member as a result of a variant or mutation…
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in a germ cell of one of the parents or that arises in the fertilized egg during early embryogenesis—to separately estimate the male and female generation times[...] So, it is saying it can measure results for male and female parents separately. But can their analysis of the "kinds" of mutations tell the difference between e.g. "30yo mother, 45yo father" or "20yo mother, 30yo father, plus lots of environmental factors that increase mutations"? The article doesn't make that clear to me. The article links to the study (at "10.0.4.102" instead of a domain name?), but the link doesn't load, nor is it on the Internet Archive... Edit: Ok, there is a working link at the bottom: https://www.science.org/doi/10.1126/sciadv.abm7047

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