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Yes. The number of breeding pairs present at one time could have coincided with a large population of human-like creatures that went extinct. The key point in

Yes. The number of breeding pairs present at one time could have coincided with a large population of human-like creatures that went extinct. The key point in your phrasing is: "There were many different hominid species alive at that time, and humans were in competition with them." If humpback whales eventually become extinct and blue whales eventually dominate global ecosystems we aren't going to say that means blue whales didn't experience a near extinction because "hey! plenty of whale-critters". A minimal number of breeding pairs is the definition of near-extinction. To imply otherwise is misleading. Homo-sapiens is not the same as Homo-neanderthalensis.

borissk 3y ago
This bottleneck occurred before the split between "us" and neanderthals - so if this small population didn't survive there wouldn't be not only modern humans, but neanderthals as well.
- daveguy 3y ago
  Ahh, yes. Good point. Neanderthals wasn't a good example. The ones that didn't survive from that point would have been called something else.
titzer 3y ago
Even then, there could have been many breeding pairs of humans that were alive and operating and their descendants just did not survive until today. As I wrote in my comment, it doesn't actually say that the population was 1280 individuals, just that some 1280 individual subset of the population passed on their genetic material to us. The descendants of the rest could have died out at any point between now and that time.
- daveguy 3y ago
  Okay. That's a valid hypothesis. Genetic information from only 1280 identified alive during this particular time seems evidentiary of a low population during a specific time more than something that "just happened". For instance, if the 8 billion alive today only propagated through 1280 alive sometime in the future you would expect a near extinction event to be the cause (we know near extinction and extinction aren't particularly rare). Is there evidence that it just happened to be 1280 from a thriving population of hundreds of thousands or millions? Edit: otherwise I'm not sure you can claim the hypothesis that a near extinction bottleneck is somehow more "misleading" than it was something that "just happened" to appear as a common event among species. Note -- near extinction does not have to be cataclysmic.
  - 22c 3y ago
    Perhaps it would help to give an overly simplistic scenario. If you have 12,800 critters all alive at one point in time, they each spread evenly to 10 different regions and then each 10x their population sizes before 9/10 of those regions experienced some cataclysmic event which wiped ALL of that group out. At no point did you have less than 12,800 critters alive, however all critters alive now show as descending from only 1280 critters.
    - totetsu 3y ago
      If 9/10ths of your population is living in doomed regions isn’t that a state of near-extinction?
      - 22c 3y ago
        The overly contrived/simplistic scenario would have catastrophic events happening to 9/10 populations certainly seems doomsday-ish but it's just meant to illustrate how overall a thriving species can still end up originating from only small subset.
saalweachter 3y ago
It's pretty trivial to fabricate a thought experiment where the genetic record looks one way and the historical record another. Let's imagine we've got a thousand islands a million years ago, each with a thousand proto-humans living on them. These islands live in peace and tranquility, with people occasionally swimming from one island to another to trade or visit or start a new life. Then one year, one island decides it's had enough of peace and tranquility. It cuts off contact with all the other islands. From this point on, everyone born on that island is a descendant of only the thousand people living on that island, instead of intermingling with the neighboring islands over time, but there's still a million people. Then, one generation, they go to war. They swim to a neighboring island, kill everyone there, and take it over, and then divide themselves between the two islands. The population drops from 1 million to 999,000. Over time, they expand to fill the two islands, and the population rises back to 1 million. A hundred years later, they decide they need another island, so they swim to a third island, kill everyone there, and repeat. Bit by bit, over the course of a hundred thousand years, the descendants of the original xenophobic island swim to each of the other thousand islands, kill everyone there, and repopulate. In the genetic record, you have a bottleneck -- everyone descends from this small starting population. In the historic record, you just have a gradual pattern of migration and genocide. At no point does the population drop much below the original million; at no point does the population of pre-humans "almost go extinct".
- titzer 3y ago
  Exactly!
- sally_glance 3y ago
  Great write-up! I wonder if it would be possible to enumerate all possible scenarios like this and assign probabilities to them. For example in the scenario described here, I'd expect the probability it actually occured to be pretty low given that the geographical facts (the world is not made of small islands) and the archeological findings (no mass graves that can be assigned to a periodic timeline) don't line up. Maybe I'm just not creative enough but somehow I feel there can't be that many different scenarios and most of them should be easily falisifieable/verifiable.

borissk 3y ago

This bottleneck occurred before the split between "us" and neanderthals - so if this small population didn't survive there wouldn't be not only modern humans, but neanderthals as well.

daveguy 3y ago
Ahh, yes. Good point. Neanderthals wasn't a good example. The ones that didn't survive from that point would have been called something else.

titzer 3y ago

Even then, there could have been many breeding pairs of humans that were alive and operating and their descendants just did not survive until today. As I wrote in my comment, it doesn't actually say that the population was 1280 individuals, just that some 1280 individual subset of the population passed on their genetic material to us. The descendants of the rest could have died out at any point between now and that time.

daveguy 3y ago
Okay. That's a valid hypothesis. Genetic information from only 1280 identified alive during this particular time seems evidentiary of a low population during a specific time more than something that "just happened". For instance, if the 8 billion alive today only propagated through 1280 alive sometime in the future you would expect a near extinction event to be the cause (we know near extinction and extinction aren't particularly rare). Is there evidence that it just happened to be 1280 from a thriving population of hundreds of thousands or millions? Edit: otherwise I'm not sure you can claim the hypothesis that a near extinction bottleneck is somehow more "misleading" than it was something that "just happened" to appear as a common event among species. Note -- near extinction does not have to be cataclysmic.
- 22c 3y ago
  Perhaps it would help to give an overly simplistic scenario. If you have 12,800 critters all alive at one point in time, they each spread evenly to 10 different regions and then each 10x their population sizes before 9/10 of those regions experienced some cataclysmic event which wiped ALL of that group out. At no point did you have less than 12,800 critters alive, however all critters alive now show as descending from only 1280 critters.
  - totetsu 3y ago
    If 9/10ths of your population is living in doomed regions isn’t that a state of near-extinction?
    - 22c 3y ago
      The overly contrived/simplistic scenario would have catastrophic events happening to 9/10 populations certainly seems doomsday-ish but it's just meant to illustrate how overall a thriving species can still end up originating from only small subset.

saalweachter 3y ago

It's pretty trivial to fabricate a thought experiment where the genetic record looks one way and the historical record another. Let's imagine we've got a thousand islands a million years ago, each with a thousand proto-humans living on them. These islands live in peace and tranquility, with people occasionally swimming from one island to another to trade or visit or start a new life. Then one year, one island decides it's had enough of peace and tranquility. It cuts off contact with all the other islands. From this point on, everyone born on that island is a descendant of only the thousand people living on that island, instead of intermingling with the neighboring islands over time, but there's still a million people. Then, one generation, they go to war. They swim to a neighboring island, kill everyone there, and take it over, and then divide themselves between the two islands. The population drops from 1 million to 999,000. Over time, they expand to fill the two islands, and the population rises back to 1 million. A hundred years later, they decide they need another island, so they swim to a third island, kill everyone there, and repeat. Bit by bit, over the course of a hundred thousand years, the descendants of the original xenophobic island swim to each of the other thousand islands, kill everyone there, and repopulate. In the genetic record, you have a bottleneck -- everyone descends from this small starting population. In the historic record, you just have a gradual pattern of migration and genocide. At no point does the population drop much below the original million; at no point does the population of pre-humans "almost go extinct".

titzer 3y ago
Exactly!
sally_glance 3y ago
Great write-up! I wonder if it would be possible to enumerate all possible scenarios like this and assign probabilities to them. For example in the scenario described here, I'd expect the probability it actually occured to be pretty low given that the geographical facts (the world is not made of small islands) and the archeological findings (no mass graves that can be assigned to a periodic timeline) don't line up. Maybe I'm just not creative enough but somehow I feel there can't be that many different scenarios and most of them should be easily falisifieable/verifiable.