There's a British comedian called Dave Gorman who tried to travel from California to the Atlantic Coast using only small independent businesses, independent stores, gas stations, restaurants, hotels etc. It took him the better part of 2 months, he nearly had a nervous breakdown and the woman who was travelling with him filming the trip for a documentary had to be hospitalised due to a back injury from sleeping on substandard motel mattresses. I call bullshit on Selina Zito's claims that that's what she does whenever she travels.
But bottlenecks are not rare. They can and do happen to any population, any species. Have you met a bulldog? In the case of humans, we can already tell that the ancestors of all of our extant groups today had to squeeze through bottlenecks somewhere between 60,000 and 120,000 years ago. And not just the very-not-diverse. But as you probably already guessed, the very-not-diverse got hit the hardest, the very-diverse the least and the not-very-diverse somewhere in between.
Here is how the groups break down: Scarcely half a million of us are very-diverse. 1.14 billion of us are not-very-diverse. 6.42 billion of us are very-not-diverse.
93-98.5% of the ancestry of humans outside of Sub-Saharan Africa (among those with no recent Sub-Saharan African ancestry, obviously) derives from a breeding population of 1,000 to 10,000, which expanded rapidly 60,000 years ago (reaching Australia and Europe around 45,000 and 50,000 years ago, accordingly).
We’ve covered the student-body’s-worth of genetic diversity that improbably went on to settle five continents and the habitable islands strung between. But that leaves all of Africa. How genetically diverse are most Africans? Scattered in their midst are tiny clusters of the planet’s most genetically diverse humans. But genetically, all other Sub-Saharan Africans more closely resemble their bottle-neck-surviving brethren who left for other continents than they do their own very-diverse geographical neighbors.
In the case of the very-not-diverse (fully 6.42 billion-ish of us), our models suggest that life on earth threw a funnel across their path, and only 1,000-10,000 lucky humans made it through the impossibly narrow neck. Our best (always provisional) models suggest they dwindled from an earlier population maybe 10 times bigger. So this round of cuts diminished the breeding pool by 90%. Think about that. Only 1,000 to 10,000 total humans could survive whatever those harsh conditions were. On a planet with 7.7 billion humans today, that small a group is a rounding error, the student body of a large high school or a small college, an isolated mountain village that could disappear tomorrow without anyone noticing. How close did we come to losing the ancestors of every single one of 6.42 billion of us alive today? Well, we came within 1000-10,000 people of it.
So the simple “Out of Africa” narrative of a population crash and explosion across the world holds for North Africans, Eurasians, Oceanians, and Amerindians, some six and a half billion of us. But the origins of modern populations south of the Sahara are clearly more complex. Any bottleneck’s effects were much weaker within Africa, and multiple proto-modern populations seem to have been separating into distinct lineages as early as 200,000 years ago.
Finally, of course, we have that most unique group, our scant half-million genetically very-diverse relatives. People like the Khoi, the Mbuti, the San, those last thousand purely Hadza humans on the planet, seem to all be descended from a population whose crash was a little gentler. Our best guess today is that when they hit a bottleneck, they probably lost 25% of their prior diversity. So, if they only fell from an effective breeding population of 100,000 to 75,000, you can see why 60,000 to 120,000 years later, they are able to retain such a massively greater breadth of diversity within their genomes than all the other 7.7 billion of us combined.
What about the millions of humans around the world, and especially in the Western Hemisphere who carry both African and non-African ancestry? Well, that’s our fourth, intermediate group. If you are among the 140 or so million humans who are, for example, African-American, Brazilian, Caribbean, etc., look at your Ancestry, 23andMe, FamilyTree etc. results. The proportions in which you are genetically Sub-Saharan African vs. absolutely anything else are your ratio of not-very-diverse to very-not-diverse human ancestry. What if you simply have an 100% African parent and a 100% non-African parent? Then you don’t even need a genetic test. You are a 50-50 hybrid of not-very-diverse and very-not-diverse human lineages.
Additionally, Africa’s small populations of hunter-gatherers (that scant half-million people from above) are very different from agriculturalists (the other 1.14 billion Sub-Saharan Africans), the latter of whom are genetically closer to all the rest of humanity than to the hunter-gatherers near them on their same continent. We don’t have an exhaustive and comprehensive model to account for all these disparate facts. At least yet.
Alone on our planet today, those maybe half a million very-diverse souls hint at our species’ one-time amazing levels of genetic diversity. In our DNA, we all contain multitudes. But once, we all contained mega-multitudes. Only the very-diverse retain much of it today.
The very-diverse are hunter-gatherer populations who live in clusters scattered across Central and Southern Africa, in Namibia, Botswana, the Congo and a dozen other nations. They include the Khoi, the San, the Mbuti, the Mbenga, the Twa and the Hadza. Inside their DNA, they carry such a dazzling diversity of single-nucleotide-polymorphisms (SNPS), that even two San from different groups both living in Namibia’s Northern Kalahari desert, and speaking click languages from the same family, are more genetically distinct from one another, by a solid 20%, than a person from Stockholm is from a person from Shanghai. That is, they average a rate of 1.2 nucleotide differences per kilobase (1000 SNPs), where a Northern European and Chinese person differ from each other at a rate of only one difference per kilobase. And the San in this example were both from the Kalahari; imagine comparing samples from peoples who live thousands of miles apart!
The founder population of today’s genetically not-very-diverse Sub-Saharan Africans shows signatures of a population crash, probably with a toll of 50% and probably from an effective breeding population of something like 50,000 people down to 25,000. So out of a founding population on the scale of a very small city 60,000-120,000 years ago, today’s 1.14 billion Sub-Saharan Africans have gone on to people every habitable space of that hugely varied continent. They are significantly more genetically diverse than their relatives on five other continents, but nowhere near as diverse as the neighbors in their midst.
Do you know which you are? You don’t have to tell me anything else about you; by the very fact that you are reading this I can almost guarantee you are in group 2 or 3. Just based on the numbers, I’ll put my money on 3. Six to one odds.
Those 1,000-10,000 human beings who made it through their ordeal, smuggled out in their nuclei all the genetic diversity 6.42 billion very-not-diverse humans among us today would have to draw on ever after. Take a native each from say Santa Fe, Stockholm, Shanghai, Ulaanbaatar in Mongolia, Uluru in the Australian outback and a Sentinelese person from the Andaman Islands and you behold a little of the amazing superficial variety of the human race. They and their relatives have peopled almost every corner of the earth. They speak a riot of different languages and they look nothing like one another. And yet, aside from a dash of Denisovan here and a trace of Neanderthal there, as far as we can tell, they all trace the entirety of their ancestry back to a single founder event about 60,000 years ago. An event when just a tiny subsample of 1,000-10,000 humans of that day passed through a brutal, extended bottleneck. Whether it was in Africa or just after leaving the continent, they burst out of that dire strait and re-peopled the globe.
Why are the vast majority of us not-very-diverse and very-not-diverse? And which is which? Genetically, all the rest of modern humanity is one of two similar flavors (or a swirl of the two) with lessened genetic diversity, because along the path to today, we lost most of our diversity. How? Severe population contraction. Inbreeding, if you must. As far as we can tell, all of humanity, at some point in the past 60,000-120,000 years was forced through one or more funnels. And most of our glorious diversity of potential ancestors didn’t survive the successive culls.
James Adomian is a super underrated impressionist.
Will Menaker sounds so young and healthy
Caught in a lie again, Mr Traphouse: the Minneapolis light rail DOES NOT go directly to the state fair grounds
The real raccoons where the friends we made along the way.
Open season on ICE agents would be helpful.
There's a British comedian called Dave Gorman who tried to travel from California to the Atlantic Coast using only small independent businesses, independent stores, gas stations, restaurants, hotels etc. It took him the better part of 2 months, he nearly had a nervous breakdown and the woman who was travelling with him filming the trip for a documentary had to be hospitalised due to a back injury from sleeping on substandard motel mattresses. I call bullshit on Selina Zito's claims that that's what she does whenever she travels.
He sounds like Da’ Maniac
Was that the My Pillow guy doing a Jesse Ventura impression?
dang this content is coming out very quickly =-)
Many an apple lass
But bottlenecks are not rare. They can and do happen to any population, any species. Have you met a bulldog? In the case of humans, we can already tell that the ancestors of all of our extant groups today had to squeeze through bottlenecks somewhere between 60,000 and 120,000 years ago. And not just the very-not-diverse. But as you probably already guessed, the very-not-diverse got hit the hardest, the very-diverse the least and the not-very-diverse somewhere in between.
Here is how the groups break down:
Scarcely half a million of us are very-diverse.
1.14 billion of us are not-very-diverse.
6.42 billion of us are very-not-diverse.
93-98.5% of the ancestry of humans outside of Sub-Saharan Africa (among those with no recent Sub-Saharan African ancestry, obviously) derives from a breeding population of 1,000 to 10,000, which expanded rapidly 60,000 years ago (reaching Australia and Europe around 45,000 and 50,000 years ago, accordingly).
We’ve covered the student-body’s-worth of genetic diversity that improbably went on to settle five continents and the habitable islands strung between. But that leaves all of Africa. How genetically diverse are most Africans? Scattered in their midst are tiny clusters of the planet’s most genetically diverse humans. But genetically, all other Sub-Saharan Africans more closely resemble their bottle-neck-surviving brethren who left for other continents than they do their own very-diverse geographical neighbors.
In the case of the very-not-diverse (fully 6.42 billion-ish of us), our models suggest that life on earth threw a funnel across their path, and only 1,000-10,000 lucky humans made it through the impossibly narrow neck. Our best (always provisional) models suggest they dwindled from an earlier population maybe 10 times bigger. So this round of cuts diminished the breeding pool by 90%. Think about that. Only 1,000 to 10,000 total humans could survive whatever those harsh conditions were. On a planet with 7.7 billion humans today, that small a group is a rounding error, the student body of a large high school or a small college, an isolated mountain village that could disappear tomorrow without anyone noticing. How close did we come to losing the ancestors of every single one of 6.42 billion of us alive today? Well, we came within 1000-10,000 people of it.
So the simple “Out of Africa” narrative of a population crash and explosion across the world holds for North Africans, Eurasians, Oceanians, and Amerindians, some six and a half billion of us. But the origins of modern populations south of the Sahara are clearly more complex. Any bottleneck’s effects were much weaker within Africa, and multiple proto-modern populations seem to have been separating into distinct lineages as early as 200,000 years ago.
Finally, of course, we have that most unique group, our scant half-million genetically very-diverse relatives. People like the Khoi, the Mbuti, the San, those last thousand purely Hadza humans on the planet, seem to all be descended from a population whose crash was a little gentler. Our best guess today is that when they hit a bottleneck, they probably lost 25% of their prior diversity. So, if they only fell from an effective breeding population of 100,000 to 75,000, you can see why 60,000 to 120,000 years later, they are able to retain such a massively greater breadth of diversity within their genomes than all the other 7.7 billion of us combined.
What about the millions of humans around the world, and especially in the Western Hemisphere who carry both African and non-African ancestry? Well, that’s our fourth, intermediate group. If you are among the 140 or so million humans who are, for example, African-American, Brazilian, Caribbean, etc., look at your Ancestry, 23andMe, FamilyTree etc. results. The proportions in which you are genetically Sub-Saharan African vs. absolutely anything else are your ratio of not-very-diverse to very-not-diverse human ancestry. What if you simply have an 100% African parent and a 100% non-African parent? Then you don’t even need a genetic test. You are a 50-50 hybrid of not-very-diverse and very-not-diverse human lineages.
Additionally, Africa’s small populations of hunter-gatherers (that scant half-million people from above) are very different from agriculturalists (the other 1.14 billion Sub-Saharan Africans), the latter of whom are genetically closer to all the rest of humanity than to the hunter-gatherers near them on their same continent. We don’t have an exhaustive and comprehensive model to account for all these disparate facts. At least yet.
Alone on our planet today, those maybe half a million very-diverse souls hint at our species’ one-time amazing levels of genetic diversity. In our DNA, we all contain multitudes. But once, we all contained mega-multitudes. Only the very-diverse retain much of it today.
Chain restaurants don't count as locally owned. Jfc
Usually franchises are owned locally, especially with places like McDonald’s and Starbucks
The very-diverse are hunter-gatherer populations who live in clusters scattered across Central and Southern Africa, in Namibia, Botswana, the Congo and a dozen other nations. They include the Khoi, the San, the Mbuti, the Mbenga, the Twa and the Hadza. Inside their DNA, they carry such a dazzling diversity of single-nucleotide-polymorphisms (SNPS), that even two San from different groups both living in Namibia’s Northern Kalahari desert, and speaking click languages from the same family, are more genetically distinct from one another, by a solid 20%, than a person from Stockholm is from a person from Shanghai. That is, they average a rate of 1.2 nucleotide differences per kilobase (1000 SNPs), where a Northern European and Chinese person differ from each other at a rate of only one difference per kilobase. And the San in this example were both from the Kalahari; imagine comparing samples from peoples who live thousands of miles apart!
The founder population of today’s genetically not-very-diverse Sub-Saharan Africans shows signatures of a population crash, probably with a toll of 50% and probably from an effective breeding population of something like 50,000 people down to 25,000. So out of a founding population on the scale of a very small city 60,000-120,000 years ago, today’s 1.14 billion Sub-Saharan Africans have gone on to people every habitable space of that hugely varied continent. They are significantly more genetically diverse than their relatives on five other continents, but nowhere near as diverse as the neighbors in their midst.
Do you know which you are? You don’t have to tell me anything else about you; by the very fact that you are reading this I can almost guarantee you are in group 2 or 3. Just based on the numbers, I’ll put my money on 3. Six to one odds.
Those 1,000-10,000 human beings who made it through their ordeal, smuggled out in their nuclei all the genetic diversity 6.42 billion very-not-diverse humans among us today would have to draw on ever after. Take a native each from say Santa Fe, Stockholm, Shanghai, Ulaanbaatar in Mongolia, Uluru in the Australian outback and a Sentinelese person from the Andaman Islands and you behold a little of the amazing superficial variety of the human race. They and their relatives have peopled almost every corner of the earth. They speak a riot of different languages and they look nothing like one another. And yet, aside from a dash of Denisovan here and a trace of Neanderthal there, as far as we can tell, they all trace the entirety of their ancestry back to a single founder event about 60,000 years ago. An event when just a tiny subsample of 1,000-10,000 humans of that day passed through a brutal, extended bottleneck. Whether it was in Africa or just after leaving the continent, they burst out of that dire strait and re-peopled the globe.
Why are the vast majority of us not-very-diverse and very-not-diverse? And which is which? Genetically, all the rest of modern humanity is one of two similar flavors (or a swirl of the two) with lessened genetic diversity, because along the path to today, we lost most of our diversity. How? Severe population contraction. Inbreeding, if you must. As far as we can tell, all of humanity, at some point in the past 60,000-120,000 years was forced through one or more funnels. And most of our glorious diversity of potential ancestors didn’t survive the successive culls.
Open season on ICE agents would be helpful.