My assumption is that most of my ancestors (if you set a reasonable cutoff in the past at the invention of farming, or written records) would be farmers because from ca. 10kya to only a few hundred years ago, most people were farmers by a huuuge margin.
The question very specifically asked for starting 300,000 years ago, not 10,000.
This seems very surprising/wrong to me given my understanding of the animalkingdom, where various different bands/families/social groups/whatever precursor to tribes you think of have ways to decrease inbreeding, but maybe you think human hunter-gatherers are quite different? I’d expect population bottlenecks to be the exception rather than the rule here across the history of our species.
I’d trust the theory + animal data somewhat more on this question than (e.g.) studies on current uncontacted peoples.
On the intuition question, my intuition was probably the other way because most of human history was non-farming, and because the vast majority of farmers (those born in the last millennium) weren’t my ancestors.
I updated my model to account for an error—it’s now a bit closer. 7.8 billion non-farmers to 6.4 billion farmers, and 4.9 billion exclusive farmers, but I still basically stand by the logic.
To respond to your question, why I didn’t pick a fixed number of personal ancestors:
We have fewer recent ancestors, assuming 16 generations, we’d have around 20k to 50k ancestors at 1600. (2^16 - inbreeding). If we want to count these ancestors carefully, we should count back with an algorithm accounting for population size and exponentially increasing inbreeding.
We could also plausibly try to use this strategy to draw a more accurate number of ancestors from 1200-1600--- this might be a period where individual/geographical differences, or population constraints, play a significant role. If you’re Icelandic, most of your ancestors in this period will still be from Iceland, but if you are Turkish, your ancestors from this period are more likely to extend from Britain to Japan. My model doesn’t do this, because it sounds difficult, and because the numbers are negligible anyway- I just estimate that 0.1% to 1% of total humans born from 1200- today were my ancestors.
By around 1200 AD, it surely becomes impractical to rely on a personal family tree to track ancestry, because of the exponential growth in the number of ancestors. Beyond that point, your total potential ancestors (in the billions, without factoring in inbreeding) massively exceed the global population (in the 100s of millions). The limited population size becomes the constraint.
So an Italian might assume that they are descended from a significant portion (40%?) of Europe’s population in 1200 AD. By 800 AD, this would extend to a majority (60%?) of people living across Eurasia and Northern Africa. By the time we reach 500 BC to 1000 AD, it’s likely that most people from the major Old World civilizations and peripheries (where the bulk of the global population lived) were direct ancestors of people alive today. My numbers could be way off, but I think this is a better way of getting in the right ballpark than trying to trace back individual ancestry. I used these figures as a baseline. https://www.prb.org/articles/how-many-people-have-ever-lived-on-earth/
You’re right that I don’t account for major bottlenecks—my assumption is that they basically even out over time, and there’s a constant 20-60% chance of humans born in each period not passing down ancestors to the modern day. If you wanted to refine this model you’d take into account more recent (e.g. Black Death) and less recent (Neolithic Y-chromosome bottleneck) bottlenecks.
Well, you can stick your own numbers into the model and see what you get—a few tweaks in the estimates puts farmer ancestors higher, as would assuming more prehistoric lineage collapses.
For example, if you think that almost everyone who had offspring from 2000BC-1200AD was your ancestor, then you get more farmer ancestors. I initially put it closer to 40% (assuming little to no Sub-Saharan or Native American ancestry, and a more gradual spread throughout Eurasia), but the model is sensitive to these estimates.
From a “Eurasia-centric” perspective, my sense is that personal ancestry doesn’t make a major difference except for pockets like Siberia and Iceland, perhaps. It’s noticeably different for people with some New World or Sub-Saharan ancestry, and wildly different if you’re pure-blooded Aboriginal Australian.
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The question very specifically asked for starting 300,000 years ago, not 10,000.
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This seems very surprising/wrong to me given my understanding of the animal kingdom, where various different bands/families/social groups/whatever precursor to tribes you think of have ways to decrease inbreeding, but maybe you think human hunter-gatherers are quite different? I’d expect population bottlenecks to be the exception rather than the rule here across the history of our species.
I’d trust the theory + animal data somewhat more on this question than (e.g.) studies on current uncontacted peoples.
Sorry, just read this response.
On the intuition question, my intuition was probably the other way because most of human history was non-farming, and because the vast majority of farmers (those born in the last millennium) weren’t my ancestors.
I updated my model to account for an error—it’s now a bit closer. 7.8 billion non-farmers to 6.4 billion farmers, and 4.9 billion exclusive farmers, but I still basically stand by the logic.
To respond to your question, why I didn’t pick a fixed number of personal ancestors:
We have fewer recent ancestors, assuming 16 generations, we’d have around 20k to 50k ancestors at 1600. (2^16 - inbreeding). If we want to count these ancestors carefully, we should count back with an algorithm accounting for population size and exponentially increasing inbreeding.
We could also plausibly try to use this strategy to draw a more accurate number of ancestors from 1200-1600--- this might be a period where individual/geographical differences, or population constraints, play a significant role. If you’re Icelandic, most of your ancestors in this period will still be from Iceland, but if you are Turkish, your ancestors from this period are more likely to extend from Britain to Japan. My model doesn’t do this, because it sounds difficult, and because the numbers are negligible anyway- I just estimate that 0.1% to 1% of total humans born from 1200- today were my ancestors.
By around 1200 AD, it surely becomes impractical to rely on a personal family tree to track ancestry, because of the exponential growth in the number of ancestors. Beyond that point, your total potential ancestors (in the billions, without factoring in inbreeding) massively exceed the global population (in the 100s of millions). The limited population size becomes the constraint.
So an Italian might assume that they are descended from a significant portion (40%?) of Europe’s population in 1200 AD. By 800 AD, this would extend to a majority (60%?) of people living across Eurasia and Northern Africa. By the time we reach 500 BC to 1000 AD, it’s likely that most people from the major Old World civilizations and peripheries (where the bulk of the global population lived) were direct ancestors of people alive today. My numbers could be way off, but I think this is a better way of getting in the right ballpark than trying to trace back individual ancestry. I used these figures as a baseline. https://www.prb.org/articles/how-many-people-have-ever-lived-on-earth/
You’re right that I don’t account for major bottlenecks—my assumption is that they basically even out over time, and there’s a constant 20-60% chance of humans born in each period not passing down ancestors to the modern day. If you wanted to refine this model you’d take into account more recent (e.g. Black Death) and less recent (Neolithic Y-chromosome bottleneck) bottlenecks.
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Well, you can stick your own numbers into the model and see what you get—a few tweaks in the estimates puts farmer ancestors higher, as would assuming more prehistoric lineage collapses.
For example, if you think that almost everyone who had offspring from 2000BC-1200AD was your ancestor, then you get more farmer ancestors. I initially put it closer to 40% (assuming little to no Sub-Saharan or Native American ancestry, and a more gradual spread throughout Eurasia), but the model is sensitive to these estimates.
From a “Eurasia-centric” perspective, my sense is that personal ancestry doesn’t make a major difference except for pockets like Siberia and Iceland, perhaps. It’s noticeably different for people with some New World or Sub-Saharan ancestry, and wildly different if you’re pure-blooded Aboriginal Australian.
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I explained why I think tracing back personal history is impractical.
Your separate method to spot check my model is just a simplified version of the same model.