Are the majority of your ancestors farmers or non-farmers?
post by Linch · 2023-06-20T08:55:31.347Z · LW · GW · 2 commentsThis is a question post.
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Answers 7 Radford Neal 7 ChristianKl 3 athom 3 noggin-scratcher 1 archeon 1 Alexander Turok 1 Cervera None 2 comments
Assume humanity began with homo sapiens ~300,000 years ago. Are the majority of your ancestors farmers or non-farmers?
My friend and I had very differing intuitions on this, and after thinking about it some, both of us currently think it's very non-obvious.
Answers
Providing a sensible answer is dependent on arriving at a sensible interpretation of the question. I'll assume that it is aimed at understanding to what degree farming or non-farming lifestyles have had an influence on the selection of genes that you carry. I assume that "farming lifestyle" includes people who don't actually farm, but obtain food from farmers, one way or another.
On that basis, and assuming you are a typical inhabitant of a society that hasn't recently engaged in much hunting/gathering (maybe some fishing, but not dominant), I would say that about 1/30 of your ancestors were of a farming lifestyle. That is, if you trace back what the selective influences were on your ancestors, about 1/30 of it was selection for reproduction in a farming community. I get the 1/30 by dividing 300,000 years of homo sapiens into 10,000 years of agriculture.
I don't think the population sizes at different times, and collapse of the pedigree (some of your ancestors being the same people), make any difference. It might make a difference if the number of children per person varied, since each child is a new object for selection, but I think this may be rather constant until very recent times. And of course, the number of children who survive to reproduce themselves is close to two at all times. (The population has grown over time, but at nowhere near the rate it would if, say, three children per couple survived to reproduce themselves.)
Now, depending on how quick evolution can act, the fact that the 1/30 of the selection influence is the most recent 1/30 could be crucial.
↑ comment by Dagon · 2023-06-20T20:57:33.104Z · LW(p) · GW(p)
Now, depending on how quick evolution can act, the fact that the 1/30 of the selection influence is the most recent 1/30 could be crucial.
This is an important insight, if that's the reason behind the question. If you break one's genetic heritage into 30 equal slices, 29 of which are hunter-gatherer, one of which is farming, and the last fragment is a rounding error too short for evolution to matter. You'll likely find that evolution is punctuated by reactions to large changes in what makes for fitness in the environment. The first slice (change from little cooperation and very low cultural adaptations to cooperative hunter-gatherer tribes with some amount of cultural knowledge transfer) likely saw a fair bit of change. The second through 29th slices saw continued adaptation to previous adaptations, but no major disruptions at the evolutionary/genetic level. The 30th slice saw a huge environmental change, and a somewhat different selection pressure.
The most recent 1/30 could EASILY have more impact than the 28 10000-year segments before it.
↑ comment by Linch · 2023-06-21T00:08:17.965Z · LW(p) · GW(p)
I'll assume that it is aimed at understanding to what degree farming or non-farming lifestyles have had an influence on the selection of genes that you carry.
This was not my question, but you're free to answer a different one! :)
Replies from: Radford Neal↑ comment by Radford Neal · 2023-06-21T14:46:31.540Z · LW(p) · GW(p)
Ahh, but without a purpose, how can one tell what the question actually is?
You could be asking about who you get by tracing back births and matings over the last 300,000 years that led to you. But do you then count people more than once if they show up more than once in this back trace?
Or are you really asking where your genetic material came from? It's quite possible that none of your genetic material came from one of your great-great-great-great-great-great-great-grandfathers. Genes aren't selected independently to be included or not in sperm or egg, but instead come in larger chunks (I think a few hundred of them), which means that it's entirely possible for the entire genetic contribution of one "ancestor" to by chance be lost in relatively few generations (of course, that means that some other ancestor contributes more than one might have thought). If you define "ancestor" as "person some of whose genes I have", then the number of distant ancestors you have is much less than you might have thought.
In the above, I'm tracing back where from a physical point of view the genes came from. But of course, the fact that the genes of some ancestor did not by a physical process result in any genes in you does not imply that you don't have some of the exact same genes as them - which you may have obtained from some other ancestor. Does that count?
Replies from: Linch↑ comment by Linch · 2023-06-21T22:48:33.170Z · LW(p) · GW(p)
Not every question has to have a purpose! :) Imagine that this is intellectual interest only, at least to me.
But do you then count people more than once if they show up more than once in this back trace?
No? This question would be trivially easy if you did lol.
Or are you really asking where your genetic material came from?
No. I personally wanted a literal answer to my literal question.
Replies from: LinchWikipedia suggests an average of 50,000 individuals for prehistoric humans in Africa. Population sizes after farming were so much larger, that I would expect the majority of my ancestors to be farmers.
↑ comment by [deleted] · 2023-06-20T22:21:47.648Z · LW(p) · GW(p)
Ah but your "ancestors" means every individual who contributed to your genetics. If "humans" existed for longer as hunter gatherers, even if there were far fewer of them, then far more generations of individuals contributing to your existence would have come from them.
Gwern points out below that since at a certain point we all share common ancestry, only ancestors who can be considered "different" can count as an "ancestor".
Replies from: ChristianKl↑ comment by ChristianKl · 2023-06-20T23:05:06.201Z · LW(p) · GW(p)
I would expect that if we go back 1000 years, then all Eurasian farming humans alive at that point are your ancestors.
Populations got much bigger post-Industrial revolution, after which very few people were farmers. I'm pretty sure more people who have existed were non-farmers just from that growth, by a huge margin.
But I'm not sure whether or not that should carry over to ancestors. On one hand, you can only have so many ancestors at a time, and explosive industrial population growth doesn't change that. But smaller farming populations might mean more of my family tree crossing over itself, and so fewer unique farming ancestors?
↑ comment by Linch · 2023-06-21T00:06:12.236Z · LW(p) · GW(p)
I'm pretty sure more people who have existed were non-farmers just from that growth, by a huge margin.
This is wrong, if we date the Industrial revolution to ~1750. According to this article, the halfway point for "number of humans who have ever lived" is likely before 1200 CE.
I would expect the general breakdown to be a few recent generations of maybe not farmers, several thousand years of mostly farmers, and then the remainder of the time between the dawn of humanity and the beginning of agriculture being "farmers didn't exist yet".
Exactly when agriculture began isn't an entirely settled question, but there doesn't seem to be any suggestion that it was early enough to make up any more than a small fraction of the last 300k years.
Even if you include some proto farming, like a hunter-gatherer occasionally choosing to scatter seeds in a convenient foraging spot, I don't know if you get back to 150kya (or whenever the halfway point would be when accounting for changing generation times, and counting ancestors rather than years)
Or are we thinking that it gets weirder when you account for population size expanding after farming? That would provide more people to be distinct ancestors (past a certain point, everyone who was alive at the time either has no living descendants or is a universal ancestor), but I'm dubious of that out weighing the long (long) period of pre-farming.
↑ comment by Linch · 2023-06-20T09:32:27.029Z · LW(p) · GW(p)
Or are we thinking that it gets weirder when you account for population size expanding after farming?
Yes. Keep in mind that there's like an order of magnitude more people post agricultural revolution.
Replies from: noggin-scratcher↑ comment by noggin-scratcher · 2023-06-20T09:45:53.276Z · LW(p) · GW(p)
That does make it more difficult. Order of magnitude (or more) more people in each generation after farming, but more than an order of magnitude more years in the period before farming.
The "if you go back far enough, everyone was your ancestor" argument only kicks in part way through the farming period whereas it would be in full effect for pre-farming. But also probably a greater proportion of hunter gatherers died without leaving any descendants, or have had their line of descendants die out in the time since.
Ok, you've successfully induced uncertainty. I don't feel able to do math to come to a clear answer.
Replies from: gwern↑ comment by gwern · 2023-06-20T20:10:29.116Z · LW(p) · GW(p)
'Pedigree collapse' happens shockingly fast. You apparently do not have to go back more than 1-2000 years before everyone shares a common ancestor and the pedigrees are all linked. So, you will have pedigree collapse in your local population well before that. This means that your particular ancestry can't matter much (since soon you'll share the same total population of unique ancestors as everyone else), only the ratios of ever-farmers:ever-nots over the total human population history. Since the non-farming lifestyle only supports on the order of millions of humans rather than billions of humans, the ratio is pretty decisive. Farming just supports much, much, much larger populations of humans, and thus, ancestors. As long as you are not too close to the Neolithic (as we are not inasmuch as farming began ~11,000 years ago), I would expect the exponential rise of the farming human population to have long ago reduced your hunter-gatherer ancestry to some extremely small percentage of 'all your ancestors' like 1%, and thus extremely far from >50%.
Replies from: Linch↑ comment by Linch · 2023-06-20T20:29:54.613Z · LW(p) · GW(p)
OWID claims that there were ~9 billion people, or about 8%, of people before the agricultural revolution. So I don't think you can get to quite as low as ~1%.
If we make the simplifying assumption that everybody in the past are ancestors, then we get 8% non-farmers. This assumption is ofc false, but if it's true across a fairly small number of generations, farmers will outweigh non-farmers as you say.
According to this article, the halfway point for "number of humans who have ever lived" is between 1 CE and 1200 CE.
Linch, unless you are African then you have 1% to 4% Neanderthal genes, there was interbreeding and presumably we had "mixed" individuals on both sides. Neanderthal (and Denisovans etc) must have had similar levels of consciousness to us so there would have been an exchange of culture. Homo Sapiens are not your only ancestors.
↑ comment by Linch · 2023-06-22T20:38:40.950Z · LW(p) · GW(p)
I'm East Asian, which likely means significant Neanderthal and Denisovan influence.
Hmm well I also have small mammal and bacteria ancestors, presumably. So we need a cutoff somewhere. But I guess with my (arbitrary) cutoff of 300K years ago, I'd also be happy to include the non-Homo sapiens ancestors, not that it's very likely to flip the final answer.
According to this, there were only 9 billion humans alive before the agricultural revolution, as compared to 109 billion who have lived and died:
If ancestor is parent/mother/grandparent etc but nothing else. Obviously non hunters.
If we count how many people dead or alive are you related to. Farmers.
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comment by Dagon · 2023-06-20T18:00:05.706Z · LW(p) · GW(p)
So, figure 25-year generations (probably too long, but this is a Fermi estimate at best), so humanity began 12000 generations ago. If you assume no consanguinity (definitely false), going backward in time each generation has twice as many of your ancestors as the previous (in counting, next in time) generation.
There have not been 2^12000 people at any point in history, or even in the sum of history. Which means we need to add some complexity. Probably a LOT of merges in that family tree (meaning it's a family directed graph, not a tree :). Far enough back, it probably stabilizes at a few hundred each generation (meaning: effectively all pairings are (perhaps distant) cousins, so ancestors are multiply-pathed and not added at each generation). But that's likely too constrictive. You get to make a modeling choice how you want to calculate that expansion.
And that modeling choice overwhelms most of the rest. So you have to figure out what elements are important to get right, and what expected experience you're trying to predict. How will this bet resolve? What will happen if you're closer to correct, vs further?
In my world, where nobody cares about the answer, but I get meaningless points for sounding smart, I'll either refuse to answer (as above), or be super-simple and say "ancestor "width" probably stabilizes at some point less than a few thousand years back, so this is likely close to "how long was humanity mostly farmers vs mostly non-farmers". Which is roughly 1/25 of the total human existence.