The idea of (at least one) population bottleneck in the evolutionary history of humans is fairly widely accepted. I haven't reviewed the paper or methods but generally their results fit the range of expectations of many in the field.
This new paper is interesting in that they developed a new method in population genomics specifically to attempt to pin down all of: the time, the duration, and the size of the population.
There are many earlier papers describing different methods for arriving at similar conclusions. The below paper used similar genetic signatures from bottleneck events such as the loss of rare alleles. Their methods were different. It explains one such process fairly well and is available to read:
> There are many earlier papers describing different methods for arriving at similar conclusions.
The paper under your link is claiming a recent second bottleneck (in addition to the out-of-Africa one at ~60kya) but the Science paper is claiming an ancient bottleneck at ~900kya. These are very different conclusions.
Note that the method in the Science paper is unable to find this second bottleneck directly in non-Africans. The authors have to fix recent population sizes to find it. This doesn't sound right. The new method is also inconsistent with earlier established methods (disclaimer: one of them is mine) which the authors don't have an adequate explanation to. More discussions at:
They are very different times, yes, but the idea of a human population bottleneck at all in my experience is foreign to most people outside of the evolutionary anthropology/archaeology/etc fields.
Is there more discussion at your link or just the single dismissal post? Maybe I need to log in?
Every Christian, Jew, and Muslim (over 50% of the world population) have the same two “bottleneck” stories in their traditions and religious texts. I find it hard to believe that the idea is foreign to most people, maybe just most people you interact with.
It's a single creation and flood story from a single Middle Eastern culture
Just because it spread across half the world by the later military and commercial success of its practicioners doesnt mean the "distant history" aspect of its mythology has any more basis in reality than gods manipulating lightning, the divinity of cats or tree nymphs (or indeed the same religious tradition's emphasis on creation as a six day process). Especially since a couple birthing children and a flood are near-universally experienced concepts that don't really have that much in common with tribal migrations and non-flood near-extinction events many millenia earlier.
this reaction here reminds me of a party in Denmark where I made a comment about the concept of a genetic eve having been found and one party goer got very indignant and explained how humans came from Africa, in short I don't think the person you're replying to said anything about the flood myth being true, they just said that the concept of a genetic bottleneck is actually pretty widespread throughout the world and many people would be familiar with the idea even if not actually believing in the story that gave them that idea.
I can't divine exactly what the OP meant, but it's a pretty common argument amongst nonbelievers that ancient religious myths (especially the Flood, also present in a handful of non-abrahamic traditions) were somehow inspired by even older oral traditions of stuff that actually happened in their dim and distant past (as opposed to the flooding they experience on a regular basis). It appears I'm not the only person that perceived that was being implied.
Regardless, I don't think "genetic bottlenecks scientists believe exist in the human evolutionary tree" and "religious stories that may or may not be interpreted literally" has much conceptual overlap, either in terms of modern people's awareness of modern bottleneck theories or in terms of links between prehistoric events and mythology which became popular much later.
I think they overlap. The assumption the stories are based on older events doesn’t have to be correct, it still makes for a familiarity with the idea. I wouldn’t mind chatting with you about this at a party. :)
Sure but I think that what was pointed by the parent post is that many people are very acquainted with the concept of human population going through a bottleneck.
Just because you learnt it in a fairy tale doesn’t mean you didn’t understand a concept.
hundreds of thousands of people have passed this information across generations, and you an individual can say "it means the same as complete fiction" .. It is hubris on your part in some real way.
It seems to me that the comment suggested (either intentionally or not) that the same event has been recorded independently in the mythologies of a few separate religions, to which the reply was that these religions have only been split from each other long after these stories have been written down, so in this regard they all should count as just a single religion.
While I’m not as familiar with Islam as the other two, my understanding is its oral history diverged long before there was any written Jewish history. So while they do have a common origin, its split was about 350 years prior to any written Jewish history and about 1800 years before Christianity.
It sounds like you actually know nothing about any of these religions!
Judaism obviously claims its story is continuous from the beginning of creation, but the timeline in its own narrative suggests approximately 7000 BC. At first this was oral tradition, but estimates as for when it was written down range from 900 BC to about 450BC.
As far as Christians are concerned, the last Jewish books chronologically were Ezra and Nehemiah, written approximately 400 BC. After the period recorded in this book, the Jews were waiting for their Messiah to arrive.
Christianity per se didn't start until after Jesus' death around (around 32 AD), and the first books were written between about 40AD and 70AD. But obviously, Christianity didn't even start until many centuries after the Jewish tradition was recorded in written form, because it needed Jesus to have been born first.
The selection of which books make up the bible today was decided upon by the Council of Nicea in the late 4th century AD, and is mostly unchanged to this day, although some religious groups also include some other books, collectively called the Apochrypha, in their bibles. Some argue these aren't important, others argue they are, but whatever in the 4th century, the leaders of the church from all around the world met up several times to choose to selection of books they felt were most important for people to know. It was mostly limited because paper was expensive then, and they wanted the minimal set that contained everything considered essential to Christianity.
The Jews continued writing and considered some books important after that point, but essentially 400 BC was the last significant event even in their canon.
Islam is much later than this, and certainly much later than Christianity. As I said above, the bible in its current form was decided on in the 4th century AD and the prophet Muhammad wasn't born until the 6th century AD. Most people date Islam to 610, which is when Muhammad recorded his first revelation. You can even see Islamic teaching that references Christianity - initially positive, recognising Jesus as a prophet from God, and later more combative when Islam was largely ignored by Christians as being unnecessary.
I've read more cynical interpretations that Muhammad was hoping to ally with Christians to avoid persecution, and when they all largely ignored everything he was saying, then he decided they too were infidels who oppose the will of God, and later parts of the Quran are distinctly anti-Christian in contrast to the earlier parts.
Muhammad also re-framed old Jewish stories (accepted as true by both Jews and Christians) in a way that tried to discredit their traditions, but paint Islam more favourably. The most contentious of these is regarding Abraham and Isaac - in the Jewish tradition, he and his wife Sarah had been childless for many decades after God had promised him that his children would have many children and become many nations. Finally had a son, and God asked him to sacrifice his firstborn as a test of his faith in God to provide another son. When God saw that he would be willing to obey him and perform the sacrifice, God tells him to stop, reaffirmed his promise to bless all nations through his son, and provided a substitute animal for the sacrifice. This is all in Genesis 22. The Islamic tradition, on the other hand, re-frames this as Abraham going crazy for some reason, trying to kill his only son after decades of being childless, and God having to stop in to stop him from murdering the son he'd been longing for for decades.
So, far from divergent history long before any written Jewish history, it's the complete opposite - Jewish history largely ends in 400 BC still waiting its Messiah; Christianity claims to be about that Messiah and covers the period from about 3 BC to around 40 AD, and was largely finished being recorded around 70 AD; Islam claims to have yet more revelation recorded between around 610 AD and 650 AD. If it wasn't for the fact that the previous believers didn't agree with the new revelations each time, you could consider them to be linear and not divergent at all, rather continuing from where the previous tradition finished.
I think you are taking a too strong stance on interpretation of those stories by holy books. What stood out to me is the case of Islam twisting Abraham story. Perhaps they were not trying to shame jewish version, but were displeased with depiction of god as "playing games" and chose to present him as "wise observer that intervenes". Just wanted to provide an extra look, but if you have some more proof/info on that interpretation (I am not knowledgeable on the subject) I would love to hear.
Hypothetically speaking, and I'm putting an emphasis on the "hypothetical" part, you could have two individuals starting a new population of arbitrary size, without ill-effects of inbreeding.
There is only one requirement. And one caveat. The requirement is that both individuals need to be free of genetic defects in their alleles, so that no matter how many generations down you go you never end up with two defective alleles in the same descendant. That is impossible in practice. Eventually you would get some diversity from random mutation and at that point you would be back to "normal" state of affairs.
The caveat is disease resistance. All of their descendants would have the same immune system. If one gets sick, they all do. Any infection will spread like wildfire, if it spreads. And nothing short of total quarantine would stop it.
There an amazing number of coincidences that have led to human life existing. I only know of the anthropic principle greatest hits from physics including The Moon, plate tectonics, distance from sun, etc but I assume there are more from the natural world of evolution.
So I wouldn’t be surprised to hear that the bottleneck population also wiped their bottoms with leaves from a tree that grows only in natural uranium ore, thereby artificially boosting their genetic diversity as well as putting pressure on them to reproduce frequently and often before they reach their radiologically reduced life expectancy of 25.
All of this in light of the very literal form of survivorship bias.
Try a few billion or trillion planets to get the conditions JUST right and there will probably be at least one getting it right. Inhabited by folks who wonder why it was their planet that had everything going for it.
Even back with Leibniz, arguing this is the 'best of all possible worlds' because it is the one we exist in that god provided. It's circular, or calls for some mysticism or parallel universes.
This seems like such a contradiction with Christians. They just do lot of hand-waving and ignore it.
Then went and read the Bible and what did I find, there were other people at the time of Adam and Eve. The Bible actually discusses the other humans that were living in other lands At The Same Time As Adam and Eve. Totally blown away.
So then, why do Christians today completely believe that God Created Adam And Even and they were the very first humans and thus Evolution is Wrong. How can you argue that Evolution is wrong, because of Adam and Eve, when right in the Bible it discusses the other groups of humans?
> I don't like to be harsh about a paper, but the fanfare around this one makes it necessary to respond.
> There are many ways to go wrong when inferring past events from genomic data; the datasets are large and noisy, and computational methods get complicated.
> Thus it's essential to demonstrate clearly that your results are not an artefact of data processing or methodology, or the consequence of overfitting to a particular aspect of the data. Simulations are a vital tool for this, and they need to show that your results are robust..
> to alternative scenarios that violate the assumptions of your model. They also need to show that the observed data are indeed consistent with the model you have inferred. Sadly, it's not clear that these requirements have been met in the paper published in Science.
It could mean more than that, or maybe not. Velikovsky had the interesting hypothesis that you could compare this histories of different traditions to see if they synchronize.
For example, joshua stopping the sun for three days, which would have been in the evening (you’d stop the sun at sunset, not at noon)… so you can look a Chinese history where it was dark for three days, or aztec history where the sun was about to rise.
He does play fast and loose with his source material (based on the ones I’m familiar with) but I think the general idea is interesting…
Written words are deemed more valid than Spoken words.
So tweets are true, but what someone just spoke to me is not-true.
Better to take stance that all communication is fallible and has noise.
Plato 'wrote' about 'Atlantis'. Written means true?
A lot of Roman Historians, like Livy, etc... Embellished or were Propaganda, or even pumped up travel guides.
Where some Oral Traditions put a great deal of emphasis on memorization and can be just as good at passing information, even if the information is also wrong.
They both have fallibilities.
The Telephone effect exists in Oral.
But in Written, it is wildly miss-interpreted.
But, if across continents, cultures, methods of communication, there are flood myths everywhere. It is ok to wonder if they are based on some common occurrence. Can we put money on an exact date and cause based on some myth? Maybe not, but we can't ignore them either.
What's the argument against the seemingly obvious possibility of instead of it being a bottleneck, it was the result of a dominant group? So for the contemporary example, something like 8% of Asian men are related to Genghis Khan [1]. And that's in a very recent time frame, and in a world that was already much more spread out than the ones in the distant past.
It seems that if there was a group that was particularly dominant (killing competitors, spreading their own genes far and wide), as were their offspring and so on, then it could easily lead to a scenario that would look like a bottleneck due to a surge of a very limited number of individuals taking over a disproportionate dominance of the human gene pool. It seems this would look near identical to a bottleneck, even if it wasn't.
Mitochondrial DNA, which most people understand to be inherited entirely along the female line, is believed to point back to some single individual female “Eve” 100kya.
> Even if most Western men don’t take multiple wives, men tend to father children with more females than females do with males, a practice called “effective polygamy”.
Maybe I'm oversensitive to men's issues, but I feel western society is very biased against men, to the point that this bias overrides basic logic.
No, "men" cannot father children with more females than females do with males, but SOME (highly successful) men father children with more women whereas MORE men are left childless than women.
But God forbid we don't portray ALL men as pigs trying to father children with as many women as possible whereas women are helpless victims to this process.
While it sounds extraordinary it's a commonly held view. Not in the sense that men (overall) are structurally oppressed but there are various places where males are disadvantaged. (Note : I am not supporting this notion, just reporting what is a popular view).
Why all the disclaimers?
Unless, you know, all the knee-jerk reactions about talking about any mens issue have very serious, negative consequences in the modern world.
Experience that it's useful to be clear what you're advocating vs explaining. Not particularly serious consequences but it's irritating when you come back to a post where you say "Holocaust deniers believe X" and find multiple people have read that as "I love Hitler". (Only a slight exaggeration). That's less of an issue here than elsewhere but one develops habits.
That would look very different genetically from a population bottleneck.
There are two factors at play: inheritance and mutation. If you had a large population of genetically similar individuals, you'd expect after a few gereations many parallel lineages each with their own distinct mutations.
Imagine everyone starts out with a gene that looks like AAAAAAAA; some lines would wind up with AACAAAAA while others wind up with AAAACAAA. In later generations you might see a gene like GACCATTA which came from that first group, whereas a gene like TTAACACG which came from the second (note the position of the C).
Alternatively, if you have a small population, mutations are going to accumulate in series. Perhaps you start out with some AAAAAAAA and some TTTTTTTT variants, in later generations you'd expect to find versions of the gene like AATCAGAT and AAACAGAAT which descend from the first line and TTTCAGTC and TGTCAGTT which descend from the second. The lineages' distinctness is conserved, but they both spent a lot of time developing mutations before they radiated.
Time estimates can get a little wonky because we don't really know what the mutation rate was at any given point in the past; we can kind of calibrate by sequencing genes of fossil specimens but there are only so many specimens of sufficient quality, and they only tell us which mutations had already occurred by that point in time. But the sequence of events is much clearer.
Killing competitors means competitors are dead. Thus bottleneck. How many competitors that group could have killed? Up to 1000 - maybe, 10000 - that would be very interesting. 2000 is still bottleneck
Killing was an extremely very poor choice of words on my part, as this certainly doesn't have to involve death. Take South Korea as a contemporary example with their publicized 0.7 fertility rate. That trends towards extinction at an exponential pace. But now imagine there was another group within South Korea that started going the opposite direction and just having massive numbers of children.
You could even create an equilibrium level (probably more theoretic than practical at the population levels in modern times, but not necessarily in ancient) where this group's fertility trends up end perfectly balancing against the rest of South Korea's low fertility trends, such that the population doesn't even meaningfully change, or maybe even increases, yet the DNA pool ends up near to 100% controlled by a tiny minority. I'm curious if and how this would look different (from a long distant DNA analysis) from the suggestion that suddenly all of South Korea just mysteriously died and these were the only people left.
By sensitive to interbreeding do you mean that's the reason why humans can't have offspring with other apes? Curious to know how this is implied by a genomic bottleneck.
I think they meant incest. If we already did our share of it in the distant past, then fun with your cousin leads to a baby with a pig's tail. Or at least it did for the Buendía family: https://en.wikipedia.org/wiki/One_Hundred_Years_of_Solitude
First time hearing about this. I'm surprised the whole region isn't massively degenerated after centuries of traditional incest. The numbers are pretty staggering
I've heard it argued that it could be the reason the middle east is the way it is now as opposed to the world's hub of scientific discoveries and great culture that is used to be.
However, that's racist-adjacent so I doubt there's any actual research or scientific basis for it. They certainly have much higher rates of genetic diseases. As noted in that Wikipedia article: "While babies of Pakistani heritage accounted for roughly 3.4% of all births in the UK (2005), "they had 30% of all British children with recessive disorders and a higher rate of infant mortality," according to research done by the BBC.[46]"
Why is the bottleneck idea widely accepted? It seems to my non-academic brain that each bottleneck would make an ongoing population less likely, as it is an opportunity for the population to die out. So it seems like us having this chat today is evidence that there weren’t too many bottleneck events. The more we would have had, the less likely it would be that humans would have survived until today. 0 bottleneck events seem most likely though that lens, 1 - less likely, 2 - even less, and so on.
As far as I understand it, the bottleneck idea is based on a back-calculation of "effective population size" in the past from existing genetic diversity in the present. (This is definitely the case in the article, which specifies "the population of breeding individuals".)
There are a couple of things that tend to be miscommunicated:
1. An effective population size of N means an actual population size that is significantly larger; children too young to reproduce, adults too old to reproduce, and nerds too awkward to reproduce are all not counted in effective population size.
2. If a group gets demographically wiped out at time T, their ancestors at time T-1000 vanish from the effective population at time T-1000, even though those same ancestors were part of the effective population at time T-1000 if you did the same calculation at time T-200.
(This is true to the extent that the vanishing ancestors don't also have other descendants in groups that survive. But the effect is quite significant - the effective size of the pre-Cherokee population in the year 1000 was much larger in the year 1450 than the same quantity, the effective size of the pre-1450-Cherokee population in the year 1000, is today. Was there a bottleneck? Sure; Amerinds in the region of the United States got wiped out. How long did that process take? When did it happen? We know a lot about the shape of the population over the relevant time period - is it something we're comfortable calling a "bottleneck"?)
So we might estimate our group of 1300 effective individuals as reflecting maybe 430 men of reproductive age, 870 women of reproductive age, plus 220 more women of reproductive age who fail to reproduce, 650 more men of reproductive age who fail to reproduce, and a few thousand children and elders not of reproductive age. And if this group later loses a war, their population could be a lot higher than that.
At minimum you need a breeding pair to keep the population going. That's a whole lot less than 1200, so from that macro perspective, I'd say it's fairly hard to wipe most things out, especially the things that have made it this far, just like it's hard for me to completely get rid of the duckweed that keeps growing in my fish tank. Even if I pluck out all the visible duckweed, there's always one or two in the filter that re-seed the population and within a few days the whole surface is covered again. Most life is a little bit like this, to the point where I don't think it's very improbable for a species to have bottlenecks. For a species to make it, surviving bottlenecks has to be a defining feature, and for the most part we are exposed to species that make it.
If you have a fair coin, and then you toss it ten times and it lands ten heads in a row, that result is no longer unlikely -- it has a probability (in whatever sense that word is now meaningful) of 100 %.
You can only judge hypotheses more or less likely in relation to each other. When you have multiple hypotheses that all explain the current situation, one may be more likely to have happened in the past than another. So if all you know is that on the first 20 tosses half were heads, you might say it's less likely the sequence was ten heads followed by ten tails, than some mix of heads and tails.
But of course, the difficult part is judging whether two hypotheses explain the same outcome. That's often somewhat subjective when it comes to historical analyses like these.
Once you've won the lottery, the odds of you having won the lottery is 1 no matter how small they were before the draw.
So, no, in other words, you can't draw that conclusion. Consider that in any instance where bottlenecks led to extinction we couldn't be here to discuss it, and so the only possibilities is that we won the lottery, whatever the odds were.
That’s an interesting point about the dependence of likelihood on the outcome.
However, a counter-argument is that if you win a lottery 250 times, it would be reasonable to conclude that the lottery is biased in your favor. If you lost a bet on a coin toss picking tails 250 times in a row, you’d assume the coin is biased.
In that case, every toss with the same outcome informs you of the bias.
So does an outcome really say nothing of the chance for that outcome?
In a similar way, our survival might say that a chance for extinction was sufficiently low each year/month/day/period. The longer we survive, the more confidently we can say that the possibility of survival was high and extinction — low.
If you knew the number of attempts, the outcome would say something of the probability.
So to your last paragraph, yes, we can say something about the odds of survival any given period, because we see many periods.
But we see only one instance of our survival, and we inherently need to be here to see it, so our survival in general for the whole period tells us nothing of how likely (few events reducing our chances) or unlikely (many such events) our survival was in the past, because no matter how unlikely we wouldn't be here to discuss the probability if we didn't survive, and unlikely things do happen.
Yes, if you look at survival as one instance, it does become difficult to say anything about the likelihood based on the outcome.
But I think it's too easy to dismiss this as survivorship bias. There are also other selection biases, which might explain the higher chances of survival of a species if an alive species is selected.
There's also the multiverse theory, or more locally, something we could call "multi-environment". It does make sense that if we were here at all, we would most likely be in an environment where we were most likely to survive. Imagine 20 planets, or 20 timelines, where some make our survival nearly impossible, some - very difficult, and some - relatively easy and likely. We'd probably find ourselves alive on a planet or in a timeline where it was relatively easy and likely.
I just read a bit more on this and it looks like the debate for whether human survival implies the low risk of extinction in the past is ongoing with good arguments on each sides. So I think I'll leave it up to more academic people than me to debate this, but thanks for your thoughts.
Whether or not there are other instances of long term survival, without having access to them, they can't form a basis for our probability calculations, so the point remains that our single survival is insufficient to use as a basis for the probability of events in our past.
And, according to the article, it's not just lucky that we survived that, but that very bottleneck could have itself produced H. Hiedelbergensis, and thus H. Sapiens Sapiens.
Which also implies that while one remote group could have shrunk to a colony of about 1,300 hominids and leading to us, elsewhere other species of humans could have survived just fine for longer, later dying out due to other exogenous pressure, perhaps from our closer ancestors.
I have read that the world's cheetah are so genetically similar that they appear to have suffered two population bottlenecks, the recent one being only 10-12Ky ago in which the population might have shrunk as low as 30-40 cheetahs.
Fun fact about cheetahs is that they’re so interrelated that any cheetah can accept a skin graft from nearly any other cheetah. They’re so similar that their immune system can’t recognize that the transplanted skin is from a different individual
Or, at one point a mutation, or a group of mutations, gave rise to a small number of super-cheetahs that interbred, and those cheetahs completely out-competed all other cheetahs.
The bottleneck consists in the fact that the present cheetahs are the descendants of a group of 30-40 cheetahs that have lived at a certain time.
There are multiple possible explanations for why the bottleneck happened.
There might have been a climate change or another abiotic cause that has killed the other cheetahs, there might have been a disease that has killed the other cheetahs, their prey might have disappeared, another predator, like lions or hyenas might have killed most of them, and so on.
Among the possible causes, both in this case and in the case of humans, there is also the possibility that there has been, as you say, some mutation that has given to a small group an unusually important advantage, allowing them to outcompete any other cheetahs, so in time only their descendants have survived while the descendants of any other cheetahs have disappeared.
In the case of cheetahs, such a cause for the apparent bottleneck seems much less likely than in the case of humans, because it is hard to imagine a decisive advantage of the mutated cheetahs. Something like one extra meter per second in maximum speed does not seem to give enough advantage over competing predators.
Or, more likely, at one point a mutation, or a group of mutations, gave rise to a small number of super-cheetahs that interbred, and those cheetahs completely out-competed all other cheetahs until the remaining standard cheetahs, that had been enslaved rebelled under the cheetah Spartacus, overwhelming and eradicating the super-cheetahs using the super-cheetah's own aircraft and other weapons, though even in victory leaving only a small number of normal ones to continue the species.
There do seem to be some evolutionary branch points in which a single occurrence of a mutation or adaptation seems to have proven overwhelmingly successful.
The one I'm most familiar with is of the integration of mitochondria into eukaryotic cells. My understanding is that all mitochondria seem to trace to a common ancestor, which would suggest that this mutation appeared once, and was so overwhelmingly energetically advantageous that all eukaryotic life descended from that single individual.
(There are non-mitochondrial life forms, including prokaryotic bacteria. But so far as I'm aware every complex multicellular life form, and quite a few unicellular ones, are all prokaryotes.)
I'm not qualified to say anything about the science, but every since reading about the theory described in "When the Sea Saved Humanity" (https://www.scientificamerican.com/article/when-the-sea-save...), something about the idea of a small band of humans holed holding on to survival near the southern tip of Africa has captivated me.
I always thought that was a nice fiction but without some serious evidence to back it up it will likely remain so. You'd expect at a minimum either some fossils with unique properties or maybe even a descendant alive today since apes are still here as well on the land. Absent both it looked like someone had a neat idea and attempted to rewrite history to match the idea based on cherry picked data, rather than that a piece of evidence was discovered that didn't match the view up to that point requiring a re-thinking of how we got here.
The accepted explanation seems to be - by far - the simpler of the two.
Is it an either-or thing? The Nature link I responded to above proposes that human ancestors were coastal dwellers for a few 10's of thousands of years to survive a climate catastrophe. How long would it take for this to start shaping physiology and behavior? This isn't my area of expertise, it's more fanciful fascination than opinion.
I never bought into the aquatic ape theory. besides the fact that its not backed up at all by fossil record, we are built runners, not swimmers. Furthermore, we are built to be vertically oriented, which is horrible for swimming. its one of the reasons why humans don't make natural swimmers.
Consider that sea levels have changed considerably over the past ~5 million years, over which the Aquatic Ape (Hardy/Morgan) hypothesis might have occurred, and might be anywhere from 100 metres blelow current levels (putting fossils underwater at present) to 300 metres above.
Plus all the other usual challenges to fossil preservation.
That record is quite probably far more partial than appreciated.
There's one situation where all apes are vertically oriented: when wading. There's a great talk by evolutionary anthropologist Elaine Morgan[1] that goes through all the weird aquatic mammal-type traits humans display.
That's not really evidence though, is it? You wade because you want to keep the largest portion of your body dry and you want to be able to breathe. You swim when you have to or when you really want to, but you walk when you can. Wading is the better option in undeep water from an energy expenditure perspective as well, and likely safer than trying to swim in undeep water.
I think the "aquatic ape hypothesis" as originally proposed is a lot weaker than people in this thread seem to think. It wasn't a proposal that humans lived in the water, merely that:
> My thesis is that a branch of this primitive ape-stock was forced by competition from life in the trees to feed on the sea-shores and to hunt for food, shell fish, sea-urchins etc., in the shallow waters off the coast. I suppose that they were forced into the water just as we have seen happen in so many other groups of terrestrial animals. I am imagining this happening in the warmer parts of the world, in the tropical seas where Man could stand being in the water for relatively long periods, that is, several hours at a stretch.[1]
So, wading hunter-gatherers.
In this - as an primarily land based creature - wading seems reasonably effective.
Yes, and that's exactly what makes the hypothesis so unlikely, all this immense adaptation for something that seems to come more-or-less for free with a standard mammalian body plan. The timescales we're talking about for such invasive changes would be far longer than available for the whole of the aquatic ape hypothesis, but is recent enough that there should be plenty of fossil evidence. I just don't buy it, but if ever someone digs up fossil proof I'll be happy to eat a hat or two. It is roughly in line for me with 'Hollow Earth' and 'Water as a fuel'. It smacks of backwards reasoning and wishful thinking.
But: it's harmless and whoever wants to believe in it is obviously welcome to do so.
It's not proof, but it is evidence. It's not a smoking gun but at the same time, there are other peculiarities that line up with aquatic-ness: the hairlessness, the extensive subcutaneous fat, the breath control, the descended larynx, the swimming reflex. None of them on their own is proof, but combined they're difficult to hand-wave away. They're each traits that are very out of place in terrestrial mammals, and at the same time very normal in aquatic mammals.
I think they're all just super useful to have in a world where 2/3rds consists of water even if you predominantly live on the land. Note that there is no driving force behind any of this other than dumb selection and mutation and that it would be very strange to first lose all this stuff upon emerging from the sea but still living predominantly in coastal areas (as we still do today!) and then to re-acquire those traits over a relatively short period of time because suddenly they are pre-requisites for survival. Much easier to take them along for the ride where they are handy all the time, as evidenced by many other mammals that have all of these (and sometimes more).
But you're right in that in theory it could have happened and like any essentially unfalsifiable theory it will likely remain that way.
It's funny because depending on which field we're looking at I probably have my own 'aquatic apes' based on how solid I think a particular theory is but without dedicating a lifetime to it I'll just take the easy way out and align with the largest body of scientists until there is hard proof to the contrary. But in some fields the theories are known to be broken and then such discussions get a lot more interesting.
aquatic animals (otters, beavers, could go on) have plenty of hair. Our lack of hair is function of avoiding parasites using our brain to protect our skin instead of fur armor.
All mammals have fat so I'm not going to get into that one.
All mamals have a swimming reflex, except even though most of them are not aquatic, their reflex actually works. humans that dont spend a long time to learn how to swim ... drown.
but there are features that are very much against us being aquatic: shellfish and fish allergies.
Most certainly they did by then. About 1.8 million years ago is when the hand axe (handheld stone axes used as weapons and for cutting) was first developed, and fire control was developed by 1.5 million years ago by earlier hominids.
It's pretty crazy to think about this: if a generation would be 25 years on average, only 5 million individuals lived during those 100k years. But today, 100k years in the future sounds like a 100x longer time than what would already be unimaginable science fiction...
No, it doesn't mean that. The bottleneck doesn't say anything about how many people were alive then, just how many contributed DNA surviving until present day. There could have been millions of individuals whose offspring eventually ended up as genetic dead ends and we'd never know, except for fossils.
I meant half a million years ago when (so the narrative goes) Big Leader Ug ruled a small band of early humans by physical force and could club anyone who wanted to mate with Ug's Womans. I was wondering if a protracted period of this could produce an equivalent genetic effect to a single population choke point under the relatively modern assumption that humans pair off.
Of course that doesn't mesh with the simultaneous narrative that humans haven't significantly changed biologically since then. You get that.
> ...if a generation would be 25 years on average, only 5 million individuals lived during those 100k years.
Related: roughly 8% of people who have ever lived are still alive today [1]. And in one year we have 25x more children born than homo sapiens in those first hundreds of thousands of years (140M/yr vs. a few millions).
That perspective - is why we can say that we live in a very busy world right now. So much human life going on at the same time in this moment. A lot more than compared with 100k, 10k, 1k and 100 years ago.
The paper places the bottleneck "between around 930,000 and 813,000 years ago" and has it lasting "for about 117,000 years" [1]. This overlaps with the bottleneck found back in 2017 (also by genetic analysis) in early Neanderthal and Denisovan populations [2][3]:
Approximately 750,000 years ago, according to Rogers, the forerunners of Neanderthals and Denisovans left the ancestors of modern humans behind in Africa to make their way across Eurasia’s expansive territory. Once on their own, something nearly wiped them out entirely; the genetic data shows the population passed through a severe bottleneck, never observed in previous studies.
Headline is misleading. The existence of a population bottleneck of approximately 1200 individuals does not imply that humans almost went extinct. It doesn't say anything about the size of the population before or after that bottleneck. In fact, it doesn't even say anything about the size of the population at that time. It just means that those 1200 individuals are the only ones that have contributed genes to the gene pool that survives today. There could have been other human populations that did not pass on their genetic material to modern humans, but were the same species as those who did. In fact, there could have been a lot of them. There were many different hominid species alive at that time, and humans were in competition with them. We have no idea of their relative number. It could have been millions for all we know.
Absent any other evidence, a population bottleneck (derived through studies of live human DNA) suggests nothing about the population at the time, or over time.
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.
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.
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.
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.
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.
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".
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.
Nice, so that's another scenario. Not sure if we should rank it higher in terms of probability though - at some point they would either have had to survive some catastrophe while all others died (basically the bottleneck scenario?) or go out and kill all the others (no archeological evidence).
According to the article, that bottleneck lasted for 100,000 years. So in your scenario, the ancestor island cuts themselves off for 100,000 years before starting the extermination.
Also the time period of the bottleneck corresponds with a hole in the archaeological record.
So while your thought experiment is possible, a bottleneck is more plausible.
I think there's actually a really trivial modification for that: every thousand years or so, one of the colonizer islands decides the other colonizers are impure, cuts itself off, and begins the cycle all over again.
Wow. That is a very powerful thought experiment. Is there any evidence that a series of very slow non-comingling death marauders. Took over a population of one million vs there just being a dangerous few individuals at one point? I feel like we haven't seen successful slow march death marauders more often than low populations.
It's entirely a thought experiment. There's no evidence for it whatsoever, and it doesn't even aim to be an accurate portrayal of even my shallow understanding of the history of human precursors.
It's just an example of a scenario where only a thousand people have living descendants today that isn't "a volcano erupted and almost everyone died" or something.
I didn't mean is there evidence in human history. But is there evidence of it ever happening with any species in any recorded natural history? Because we have lots of examples of near extinction crisis.
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.
The number is also referring to effective population size vs the true population size which is larger. For reference the effective population size today is estimated to be between 10,000-20,000 individuals.
IMHO you're only partially correct. The population of our ancestors was larger before and after the bottleneck. And it's a very important event, no doubt modern human genetics and behavior is influenced by it.
The romantic optimist in me will keep some hope out that that sort of thing was the Great Filter which felled so many of our unseen galactic neighbours.
The Great Filter is really just an arbitrary speculation since we don't know most of the parameters in the Drake equation with any certainty.
It's also a fallacy to assume that a great filter, if it exists, must be a single discrete climactic test or have a single explanation. It could be that there exists on average a continuous low probability of an event or evolutionary path that rules out advanced intelligence in a given biosphere.
Let's say that the yearly probability of such a terminal event or path is about 0.00000002%. Over 500 million years this would amount to a 99% chance of failing the great filter.
If this is true it would mean that we're almost there, very likely to succeed, but also very likely pretty alone at least in our galaxy since there won't be that many advanced intelligences around.
The difference though is that unlike the discrete great filter hypothesis there is no single apocalyptic event to fear. It's a small probability spread over aeons.
This is just to show that we don't know the answer to the Fermi paradox at all. There's no testable or scientific answer at least. Only way to really know is to go out there and look around.
There may be 99% chance of failing the great filter in the 500M years before an industrial evolution and 99.99999999% chance of failing it in the 10K years past. Humankind invented nuclear weapons and had a lot of luck that they are hard to make and so far only 2 were used in anger. There's a good chance that with the progress of AI, nanotech, CRISPR very powerful weapons will become available to groups like ISIS - greatly decreasing humankind's chances of survival.
How do you actually get a number like that? What are the computations, simplified? Is it a coincidence that 1280 = 2⁷ * 10? (I mean, it makes me wonder if it isn't basically a result of using some sort of a decision tree splitting some set by 2 or something, and 10 is perhaps just some hard-coded into the model assumption — which it most probably isn't, of course, I'm just wondering: what is that number?)
1280 is the nearest threshold we can estimate to, for the reason you've describe. In the OP's title it suggests "exactly 1280", while the original published piece in Science[1] uses the phrase "around 1280".
According to current consensus, the Finnish population has gone through several bottlenecks. There might have been just two surviving paternal lineages from the bottle neck 4000 years ago. And after that, there were plenty of times when only a 1/3 or less survived the famines related to wars and plunders.
So, interestingly, Finnish DNA is an isolate but highly diverse within itself.
I wonder if it was 1280 in one community or split across several disparate and possibly warring groups.
I suppose competition from other hominid species might have pushed one community to band together for survival.
I just can’t imagine one community of any size surviving for very long without carving up territory and battling for scarce resources or hoarding to create artificial resource scarcity.
We’re such a fractured and combative species. If we were down to 1280 today I think we’d still figure out how to fight each other.
Remember that Black Monolith in 2001: A Space Odyssey? 1280 Individuals is in the realm of what some alien mission could do in terms of genetically a bunch of apes to become smarter
Offtopic: I switched to the scifi/fantasy genre and wonder why the number is not 1024 or 2310 (2 x 3 x 5 x 7 x 11) or other number based on series such as Fibonacci.
The closest from Wolfram Alpha is: 1280 has a representation as a sum of 2 squares:
1280 = 16^2 + 32^2
A long time ago there was a Sci-Fi story about the first humans crash-landing in Africa and fighting for survival among the hominids. I think the number of people on that ship was about 2k.
Is that one of the subsequent Hitchhikers Guide to the Galaxy books (satirical scifi)? Like we're all descendants of lawyers and other undesirables (iirc a civilization put all the lawyers on a ship to go to the sun, but it went off course and landed on earth?)
The article says: "Of greater surprise is the estimated length of time that this small group survived. If this is correct, then one imagines that it would require a stable environment with sufficient resources and few stresses to the system."
Maybe they were kept in a nature preserve run by friendly aliens, until the climate got sorted out ?
This is the number supported by DNA evidence. There will be a margin of error.
The bigger issue, for me, is that I'm not sure how they can rule out the possibility that there were lots of other people around at that time whose lineages gradually died out. Modern genetic lineages may trace back to 1280 people (+/- the margin of error), but it seems pretty dubious to assume that those were the only people living at that time. It seems highly likely to me that there were infertile people, people who died young, people whose only living children were infertile or died young, etc.
(I did not read the original paper, so maybe they accounted for this, or maybe they that specify that this was a genetic bottle neck for modern humans, but not necessarily the actual size of the population.)
"1280 people" is just a misleading simplification early in the linked article. Both the news article and the original paper speak of 1280 breeding individuals.
Also, the way population dynamics work, lineages tend to die out quickly or not at all. Isolated populations can die out gradually, but it takes exceptional circumstances for a population to survive in the long term while remaining isolated.
There is a minimum in the fossil record at that time. There may be other explanations for it, but one very reasonable one is that there just weren't very many skeletons to potentially fossilize.
Certainly. However, I am still highly doubtful that there were only 1280 people alive at that time. I'm not sure that this is what the article is claiming; however, it is written in a way that makes it very easy to come away with that message (as evidenced in this comment section).
What are the chances that every person alive today, for example, will still have living descendants in 400,000 years? If people 400,000 years in the future do a genetic study on themselves to determine how many of their ancestors were alive in the year 2023, what percentage of the 2023 population will they be able to account for? My guess is a fair bit lower than 100%.
"there were lots of other people around at that time whose lineages gradually died out"
It seems to me that if those lineages aren't in the DNA data, then they didn't --in the intervening years-- intermix with the lineages in the DNA data.
So, ipso facto, those lineages went extinct, and the 1280 ancestors posited in the study are the non-extinct lineages. QED.
Now, that doesn't necessarily mean they were isolated from each other, however. If we suppose that the population was actually 5000 people (just an example; I have no idea if this is a realistic number), then some percentage of those people died with having children, some may have seen their children die, etc. Of the 1280 people who still have living descendants, many of them would have had children with those people who did not, but those children (or grandchildren, etc.) eventually did not have any children themselves.
Within your own social circle, you likely know some people who will still have living descendant generations from now and some who will not.
If those lines died out from intertribal competition though, it wasn’t a near-extinction era. Some slightly less competitive group could have made it into the present day in that case.
I'm not saying it's an issue with the research. It's very likely the researchers thought of this.
It IS an issue with the article linked here, since it does not explain the research and causes readers to walk away believing there were only 1280 people.
The actual linked article isn't the paper, and doesn't even name the paper as far I can tell, it's just given as "Hu, W. et al. Science 381, 979–984 (2023)." in a footnote.
This is the actual paper, which (presumably, I cannot access) is specifically about how they made the estimate: Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition:
It's obviously the result of Roll Call:
SMITH Here!
JOHNSON Here!
WILLIAMS Here!
BROWN Here!
JONES Here!
GARCIA Here!
MILLER Here!
DAVIS Here!
RODRIGUEZ Here!
MARTINEZ Here!
HERNANDEZ Here!
LOPEZ Here!
GONZALEZ Here!
WILSON Here!
ANDERSON Here!
THOMAS Here!
TAYLOR Here!
MOORE Here!
JACKSON Here!
MARTIN Here!
LEE Here!
PEREZ Here!
THOMPSON Here!
WHITE Here!
HARRIS Here!
SANCHEZ Here!
CLARK Here!
RAMIREZ Here!
LEWIS Here!
ROBINSON Here!
WALKER Here!
YOUNG Here!
ALLEN Here!
KING Here!
WRIGHT Here!
SCOTT Here!
TORRES Here!
NGUYEN Here!
HILL Here!
FLORES Here!
GREEN Here!
ADAMS Here!
NELSON Here!
BAKER Here!
HALL Here!
[ ... ]
ROSADO
[ ... Crickets ... ]
Many were increasingly of the opinion that they'd all made a big mistake coming down from the trees in the first place, and some said that even the trees had been a bad move, and that no-one should ever have left the oceans.
Human evolution science keeps expanding for the longest time it was thought Africa was the origin. It is seeming more like a global phenomenon as time passes. I have said this a lot. Don't look at Earth from today's lens, look at it from the 900k years ago lens. What animals were around, what sort of animals we hunted and sought after. How communities were formed and how we were able to safely breed. The answer is less complicated, we had a lot of closely genetic relatives all over the planet which we reproduced with creating a various diverse human race. And we is as in past caveman like ancestors. I am not refuting the earliest ancestors found in Africa, I am just pointing out it is easier to find ancestral sites from an undeveloped part of the world.
Even China has dug fossils of ancient humans, but we have yet to really put that to study.
However again Africa is the perfect place to find the ancient human origins because it has had less human development in terms of civilization than the rest of the world.
This new paper is interesting in that they developed a new method in population genomics specifically to attempt to pin down all of: the time, the duration, and the size of the population.
There are many earlier papers describing different methods for arriving at similar conclusions. The below paper used similar genetic signatures from bottleneck events such as the loss of rare alleles. Their methods were different. It explains one such process fairly well and is available to read:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2842629/