Chris, so appreciate your making this post as it coincided with me having a week or so to really drill down on this climate change issue. I listened to your podcast with Charlie Zender first. Terrific.
I've listened to many others and done a lot of reading. Suffice to say I'm significantly less anxious about climate change than I was two weeks ago.
A few additional resources you might find interesting: Steve Koonan speech to the GWPF in November of 2021. A data-rich presentation. I think you'd like it. Around minute 25 he addresses SW US droughts and specifically mentions the impact on the Anasazi Indians circa 1100.
You might also like the 4-hour climate conversation between Lex Fridman, Bjorn Lomborg and Andrew Revkin. It's episode #339. Absolutely worth the 4 hours.
Useful to contemplate how we are allocating our resources versus building resilience, and how the west is allocating resources, toward CO2 reduction specifically, that are unlikely to have a meaningful long-term impact. Meanwhile, there are plenty of other immediate impact problems that we can solve with significantly less money. E. G. Tuberculosis.
As you note, we live in a ever-changing world. We also live in a world of limited resources. Over focusing on one issue by definition means under focusing on others. Thanks for all you do!
To me parts of town where the paint is chipping, sidewalks are cracked, fences are saggy, and grass is abundantly tall appear to be islands of change in a sea of stability. But when you look at the rich parts of town you realize that the trimmed grass, fancy fencing, recoated buildings, and smooth sidewalks are really just the illusion of stability that requires huge amounts of energy to maintain.
This is true and yet the way change is framed is as important as the change itself. I find myself in the very awkward position of disagreeing with Chris on a couple of points. Most natural climatic cycles don't cause chaos everywhere without a moment’s notice. Much of what paleoanthropology is coming to grips with is the fact that using ice core samples in Greenland, for example, allows us to understand an average state of climate but that it shouldn't be used as a proxy for every ecosystem. As they gather more samples, anthropologists are realizing that entire regions were often unaffected by seemingly large climatic events. This is causing evolutionary anthropologists to reconsider certain assumptions about human evolution.
My point is just because glacial sheets expand doesn't mean its mass chaos everywhere. One reason is the rate of change. If you look at the glacier/interglacial figure, the high interglacial peaks to low glacial peaks are usually 50k to 25k years apart. There's no doubt this causes massive change, but the consequences exponentially amplify if these peaks and valleys were to occur in 2k or 5k year increments. I've been thinking about how we perceive time on geological and evolutionary scales and how creating narrative around scales results in the discounting of time (I think it will be the first episode topic of my podcast).
Really the biggest point I have to make is when it comes to the Toba eruption and its effect on humans. I'm surprised that this hypothesis is still so popular. I know the likes of Randall Carlson and Graham Hancock continue to push it but in 2022 none of the evidence supports it. Paleoanthropologist John Hawks has a great blog discussing this topic https://johnhawks.net/weblog/the-so-called-toba-bottleneck-didnt-happen/
I won't go on about it too much other than to say that the cooling event that Toba supposedly triggered appears to have already begun before the eruption, the supposed population crash is now closer to 50 kya and is due to the out of Africa migration bottleneck rather than a population crash. The foundation of the hypothesis is based on early models that were constructed in 1992. With more current data the impact of the Toba eruption, on humans and most other ecosystems, appears to be minimal.
When I think about the Toba eruption one thing that always comes to mind is Sumatran orangutans. These apes have called this region home for millions of years. When evolutionary anthropologist Herman Pontzer compared the metabolisms of all the great apes, he found that orangutans had, by far, the lowest metabolism (with humans having the highest.) In fact, the orangutan metabolism is so low that its closest comparison is to that of the sloth. I find it hard to believe that if Sumatran orangutans (or Bornean orangutans for that matter) survived the wrath of Toba, and right on its doorstep, it would still somehow devastate Homo sapiens over 3,400 miles away in Africa. Yes, a layer of ash from the Toba eruption exists across much of the earth but that doesn't say anything about the effect, or lack thereof.
The link to John Hawks' blog (above) will do a better job of laying out specific arguments against the Toba hypothesis. Nonetheless, I'll address it from a more basic standpoint.
Direct sequencing is near impossible. The oldest human DNA comes from the Atapuerca cave in Spain. This very early Neanderthal DNA is about 430,000 years old. The record for the oldest ancient DNA to be sequenced, of any type, was recently broken. This environmental DNA (think of DNA embedded in cores of soil) was used to reconstruct a 2 million year old Greenland ecosystem.
Quite old DNA (120-30 thousand years ago) has been sequenced from both fossil remains and soil in regions like the Altai mountains of Russia (Neanderthals/Denisovans), and the Bacho Kiro cave of Bulgaria (Neanderthals/sapiens).
Unfortunately DNA rapidly degrades in hot and/or humid regions such as Africa, the Levant, etc. The oldest African DNA sequenced is only about 20,000 years old. Because of this, population size and migrations is mostly inferred through genetic sequencing of current populations.
The various arguments of the Toba hypothesis don't really line up with much of the available evidence. Different versions make slightly different assertions. For example, one argument states that about the time of eruption Homo sapiens, as a species, experienced a bottleneck and between 2,000 and 10,000 individuals survived. This argument can immediately be discarded as this argued size was already within the known range of human populations. Genomic analysis indicates that our ancestral lineage, up to 1.2 million years ago, was always a very small population with no more than ~18,500 sexually mature individuals. https://www.pnas.org/doi/full/10.1073/pnas.0909000107
And the paper that analyzes the genomes of ancient Africans (linked above) also shows an estimated range of ~2,000 to 18,000 (but shows it is likely on the higher end of the spectrum). When dealing with our species as a whole, our population was already small.
However, this population size of 1,000-2,000 probably didn't come out of thin air. Using the Tibetan ancestral lineage as an example, you can kind of guess where they got this number and argument. The out-of-Africa bottleneck has been known to have occurred sometime between 100k years ago and 50k years ago. Most current research seems to point to sometime after 65k years ago. The ancestral Tibetan lineage experienced two bottlenecks. The first being the initial out of Africa bottleneck that all Eurasians experienced. One estimate has this migrating population at only about 1,860 sexually mature individuals. About 50k years ago this Eurasian population split into ancient Europeans and Asians (the ancient European branch appears to have gone extinct). After the split, the Asian branch appears to consist of about 1,000 sexually mature individuals and would go on to reach an equilibrium of about 7,000.
With all this genetic information, which has nothing to do with the Toba eruption, it appears to me that the proponents of the Toba eruption are trying to shoehorn the theory into a narrative where the eruption is the cause of already occurring population dynamics. There was probably never a population "collapse" within Africa. If this was the case, African genetic diversity would be much reduced. Instead, genetic anthropologists, paleo-geneticists, and population geneticists see that as populations moved away from Africa, (I.E. Africa -> the Levant -> Asia/Europe -> North America -> South America) genetic diversity reduces. This is a result of continuous bottlenecks and new founding populations migrating into distant regions.
I've mostly read these research papers for other purposes, but after having read them and seeing the Toba argument I feel the need to push back because the data doesn't really support it. Especially when it's someone like Graham Hancock and Randall Carlson who are front facing towards the general population and are keeping these ideas alive. When you throw in archeological evidence and climate data it makes the argument even weaker.
With DNA and climate analysis technology improving exponentially every year, concrete answers to many questions are likely to emerge.
It's been a few years since I read David Reich's "Who we are & how we got here", in which he invokes a current "ancient-DNA revolution" that now makes it possible to use far more recent DNA to interpret past events.
For example, apparently this Eurasian population you mention split, with one group headed west (basically us Europeans) & the other east. He says that this explains why Europeans are more closely related genetically to Amerindians than to East Asians since it was a different population that spread into East Asia & stayed there, while the eastward post-split migration of the Eurasians basically headed across into the Americas.
Reich also says, for what it's worth, that they've discovered a small area buried deep within the anterior skull where you might find DNA that has lasted while everything else has degraded. All you have to do is find that part of a skull...
So I was thinking that if you looked at the DNA, even today, of various populations around the world, then considered Youngest Toba eruption (74,000 years ago) and calculated Who-Where would be most severely affected by it immediately, & Who-Where might have best ridden out its affects over the long term, you could assess the validity of the hypothesis that way. Am well aware that this wouldn't be an easy thing to do but it might be a way for proponents of the Toba catastrophe hypothesis to test it.
Reich certainly makes it sound as if there's been a great deal they could divine in recent decades that had been simply inaccessible previously.
There's no doubt that advanced computation is allowing recent DNA to provide more predictive value. But its also true that improved DNA sequencing is really driving the explosion of data in ancient DNA and especially environmental DNA. I've come across studies where stretches of ancient DNA as small as 35 base pairs in length are reconstructed into a single genome. That's insanely small! Imagine the ease of putting a 100 piece puzzle together. Now imagine putting a 10,000 piece puzzle together.
The petrous bone does seem to conserve DNA more than other bones. Reich's lab was actually criticized when the amount of these bones, which his lab destroyed
trying to sequence DNA, became public. Part of the criticism was the fact that if you destroy specimens now you won't be able to apply advanced technology to them in the future. It's a common practice of geneticists and even paleoanthropologists to leave some portions of a dig/specimen intact in order to give future generations a better chance of securing DNA or dates from dig sites.
When it comes to ancient, or fossilized remains, any DNA that can be obtained has already been sequenced. In fact, most of the sequenced DNA is available to the public and can be analyzed using online tools such as the NCBI online tool https://blast.ncbi.nlm.nih.gov/Blast.cgi
The great thing about having all this DNA available in a database is the fact that it can be mined for secondary uses. There's a ton of information on so many species: Mammoth, mastodon, Homo sapiens, Neanderthals, Denisovans, and countless other plants and animals. There are signals in the data for ecosystem collapses and extinctions but none that match near the ~74 kya Toba eruption. For instance, there are probably dozens of papers that document a collapse in population of eastern Neanderthals (a region that was already one of the coldest occupied by hominins). But this occurred 120-100 kya. The data even shows that a group of European Neanderthals migrated east and eventually took over the areas formerly occupied.
Using environmental DNA sequencing another study basically documents the last stand of the woolly mammoth in the Siberian Tundra. As the ecosystem changed from an open grassland to woodland the mammoths appeared to cling to the grassland until it too disappeared, and they with it, about 4,000 years ago.
Yes, it's natural enough, I guess, that people interested in X then discover Y, & say "Bingo! X+Y = Z". It reminds me of the hypothesis that the Chicxulub asteroid caused dinosaur extinction. Does seem pretty convincing. But there remain geologists who doggedly favour the Deccan Traps as the cause.
All this is fine provided everybody can keep ego out of the discussion.
Absolutely! I think it also matters in which order something is learned. I've casually read a science article, that I have no particular opinion on, and when reading a second article (on the same subject/announcement) I've found myself almost unconsciously disagreeing with the second article because it didn't agree with the first. Then I think to myself "So, if I would have read the second article first I would be disagreeing with the initial articles points?" And this happens on topics that I have no particular opinion or attachment towards. What happens when it's on a subject that you have actually invested time and resources in? I think this is a big driver of science that we are all mostly blind to. It's also why it seems to take the next generation to reconsider such theories and assumptions.
Wow. Thank you for this. A question I've always had is around this concept of how many individuals were in a given bottleneck population. When you write, "about 1,000 sexually mature individuals," do you mean that the DNA of around 1,000 people is detectable in downstream genetic information? In which case, it's not that there were 1,000 people, but that only 1,000 people had offspring whose offspring survived and so on down the centuries? Otherwise, how do we know how many people were alive and DID NOT have offspring who carried their DNA into the distant future? I find this confusing.
I'm also confused by the notion that human population levels were as low as 18,000 people a million years ago. Why would the population be that low in Africa, when even today, when much of the continent is uninhabitable for any primates other than humans, there are far more chimps alive (estimates range from 200k to 300k). Such a low base population of early humans seems counter-intuitive to me. Maybe you can help me see this better.
Lastly, WHO ARE YOU? Are you a geneticist? You are obviously very well-versed in this stuff. I'd love to know more about your background, if you are willing to share.
I am definitely not a geneticist although I work very hard to understand ancient DNA. I just find human origins fascinating and currently research it as a hobby. After high school I joined the Air Force and became a radio frequency/signals communication technician. After four years I left the AF and that's still my day job in the civilian world.
In 2016, I decided to get a BA in evolutionary anthropology which I finished in 2020. My undergrad thesis was on the evolution of running, which was an absurdly broad topic and a terrible choice as a thesis topic. But in the long run, it was the best choice I could have made as each section was an introduction into what we currently know about the different aspects of human evolution. Brain growth/organization, energetics of bipedal walking, the reduction of body hair, sweat gland emergence, dietary shifts, etc. I've been going down these different rabbit holes for the last five years or so.
The last two years I noticed how ancient DNA and environmental DNA research was exploding so I went back to school and got a certificate in Computational Life Sciences. I completed that earlier this year. I'm definitely not an expert but just someone trying to understand this stuff enough to figure out what the hell happened in our ancestral lineage. With that being said I've probably learned more by wading through studies and having my mind blown by the information that I find. The plan is to apply to grad school this year. But either way I'll still be learning on my own. I tell myself I am researching to incorporate what I learn into writings or YouTube videos but find that researching is too fun to stop and create a finished product. I have managed to create some mediocre videos. This one on the Denisovans is relevant to the discussion we are having.
(Notice how I hypocritically indicate an out of Africa migration at 70 kya. I am planning a whole series on out of Africa migrations where that will be updated.)
I also maintain a blog that is mostly just random ponderings on human evolution dawnofsapiens.com
I actually think that understanding population size is one of the hardest aspects of genomic analysis. Math has never really been a strong point, but it is still interesting to see how it is done. Researchers aren't actually detecting individual genomes downstream. They pick different aspects of DNA to run different analyses. If I'm really trying to understand I'm likely to read a section 10 times before I even begin to grasp what the research is getting at. For example, in the paper that predicted an effective population size of 18,500 individuals, https://www.pnas.org/doi/full/10.1073/pnas.0909000107 they use rare events known as Alu insertions. By measuring the length of the haplogroup that an insertion resides on they can determine genetic diversity and population size. Another way of measuring is by dividing the genetic diversity of a population by four times the average mutation rate.
These calculations get very convoluted and to be honest, even when using freely available online computational tools you don't really need to understand the algorithms. Just input the variables and wait for the results. At some point I'd like to ask a geneticist, such as John Hawks, to explain effective population predictions.
I should add that effective population only determines the average breeding pairs of a population. For a group like the San (according to information that I've read) 1/3 of the population is adults, 1/3 is children, and 1/3 is elderly (it's not that unbelievable). So, in this case the effective population size would more than likely predict only about 1/3 of the actual population size (depending on how you treat elderly males). Even accounting for this 1/3rd prediction, effective population can sometimes become nonlinear with absolute population. It's not a perfect measurement for absolute population size but so far it's what I have seen used in the academic literature. It can at least be used to make relative comparisons among different populations or species.
Your point of unaccounted for individuals is well taken. There are several hints of archaic Homo sapiens groups that are unaccounted for in such genetic analyses. For instance, the skull of a Homo sapiens individual was found in Greece and dated to about 210 kya. This individual, and likely others, left Africa well before the more well-known out of Africa migration. How many were in this group? And how many other such groups existed that aren't recorded in our genomes? It's hard to tell. On the other hand, even some previously unknown branches would be captured by genomic analysis.
For example, in 2021 a paper was released that analyzed several individuals from the Bacho Kiro cave in Bulgaria. They were dated to ~45 kya. When they analyzed their genomes, they found that they were, surprisingly, more closely related to East Asians and Native Americans, than to modern day Europeans. Other remains in the area that are dated to about ~40 kya are related to modern day Europeans. This indicates that the ancestral East Asian population split at least 45 kya and one group continued to East Asia while the other turned toward Europe. This European branch went extinct. But a genomic analysis of the population before the split would have still accounted for the European bound individuals.
I think most population figures given are on the low side. But everything I've seen does seem to indicate that hominins were a relatively small population, overall, when compared to other species.
Several points come to mind as to why this might be the case. Both are ecological in nature. One, with the number of bipedal species we are learning existed alongside Homo sapiens (and especially early Homo sapiens) we should consider the niches they fill as well. This isn't the sexy argument of human agency where humans go to war with other bipedal species and push them out, but I think not viewing our species as integrated in their environment is a mistake.
The anatomy of the different species offers clues to their niches. For example, Homo naledi is dated to about 230 kya in South Africa. They are well suited to bipedal locomotion and yet they retained longer arms and curved fingers for climbing. To me this indicates they inhabited more wooded areas of Africa (similar to the habitat of our ancestors the australopithecines). It appears that Homo erectus, or its derivative Homo heidelbergensis, was also still kicking in the early years of Homo sapiens. They would have kept our ancestors from expanding to an extent.
But what I've really been thinking about lately is the influence of the environment itself. This is the most overlooked and ignored aspect of humans, both today and in the past. Moving into open territory would have exposed our ancestors to predators. This likely had an effect on population. But the most important factor that shaped human beings and their ancestors is the change in density of food in savanna environments.
I’ve conducted some preliminary research on savannah chimpanzees and am amazed at how a change of environment shapes the behavior and demography of the species. For example, the population size reduces dramatically to an average of 29 individuals compared to 90 individuals for forest chimpanzees. During an online lecture I asked a primatologist about the difference in behavior of forest chimps versus savannah chimps when two groups meet at the edge of territory borders. She stated that because savannah chimps require such large territories, to support even small groups, that they rarely encounter other populations. But even when they do run into each other violence is rare and dominance displays are usually as far as things escalate.
The open savannah requires much more physical activity to survive. Chimpanzees are much less active. I would argue that high activity levels reduced fertility. Evolutionary Anthropologist Herman Pontzer’s work has showed that the Hadza (and many other physically active populations) have sex hormone levels that are up to 30% less than industrialized populations. These are healthy individuals but their metabolism goes elsewhere and this likely results in less babies. In the book Nisa: The Life and Words of a !Kung Woman, Nisa points out that sex in San populations rarely resulted in pregnancy. Different environments may change the results but then again Neanderthals and Denisovans appeared to have even smaller group and population sizes. Even human groups that live in rainforests such as the Piraha and African Pygmies don’t really see expanded populations. They even have reduced life spans where 45 years really is old.
By the way, I reached out to Professor Alan Rogers, who is a coauthor of
one of the papers I linked to earlier. I asked if he could point to something that broadly explains the science of population inference through DNA. He directed me to this tutorial he made for one of his classes https://arxiv.org/pdf/2201.02668.pdf
So far I've only briefly skimmed it but it looks like it does a pretty good job of laying the science out.
Brilliantly put point. It's always good to be reminded of the instability of this world. Buddhism is always doing that, because it's only when you wish/hope/believe that this life is anything other than unstable and difficult, that you get into REAL trouble.
Just a tiny revision for anybody who searched for "Apocalyptic Earth: Field Guide to the Future of the Earth" & couldn't find it. I found it under the name "Apocalyptic Planet: ...". I'm sure most would have just searched the authers name & found it anyway but just in case. Thanks for another great, thought provoking read Chris.
When it comes to things being fine or stable, it depends on the perspective one takes. It is very unlikely that a rapid planetary change would happen within persons lifetime. So things are usually stable from that point of view - and fine. When the shit hits the fan, life becomes a struggle, people need to rely on each other and life becomes charged with meaning - which is fine too. In both cases one could overly concentrate on finding the negative, but I don’t think it does any good and may even hinder people living a life of fullfilment and harmony with nature and fellow humans. Even rocks start to look like liquid if you consider wide enough time frame. Choose the outlook that serves you the best, focus on the moment and enjoy the ride.
Yes. I find it both profoundly sad and beautiful at the same time, both scary and comforting. It’s an acknowledgement which demands us to dive deep into the human experience. Every time I find myself wasting time doing meaningless things in front of a screen, I feel like I’m betraying it. It’s a time to make some changes.
This is great - I really appreciated hearing the Charlie Zender ep too!
Please forgive me for this, but it’s a bugbear of mine about climactic/climatic. ‘Climactic’ refers to ‘climax’, whereas ‘climatic’ refers to the climate. Although the idea of an extra-ordinary climactic situation sounds quite... exciting, no? Anyway, as a fellow word lover, I’m hoping you’ll take this as in the positive spirit intended; I do not actively want to be a dick 🤪
Craig Childs' writing is beautiful -- I've read The Way Out and The Secret Knowledge of Water, both outstanding, intimate portraits of desert exploration and the ways of water in the arid Southwest.
According to this website "https://www.theworldcounts.com/stories/how-many-babies-are-born-each-day" which shows the number of births on the planet each day clocking over in real time at an absolutely ridiculous rate of knots, we need approximately 1.79 planet Earths to provide adequate resources & absorb our waste. I'm not sure how they calculate that but if true would indicate the ideal maximum human population would be not much more than half the current number. Try telling that to everyone who believes "there's no overpopulation, the entire human population could comfortably live in the state of Texas alone"
I think in reality it is a bit more complicated than that. In many developed countries population growth has plateaud. Educated women are having fewer children because they don’t need that support around them. Some even think that we might be hitting the peak population at the moment, since in countries like India and China people are moving more and more to the cities and joining the workforce, thus earning a decent living and not necessary needing children. The absence of the old thriving village communities has already increased the ”greening” of the rural areas in those countries. Nature takes back the vacant lands. If you look at the places where there is most war and most health issues, you see that in those places people also are having more children.
Chris, so appreciate your making this post as it coincided with me having a week or so to really drill down on this climate change issue. I listened to your podcast with Charlie Zender first. Terrific.
I've listened to many others and done a lot of reading. Suffice to say I'm significantly less anxious about climate change than I was two weeks ago.
A few additional resources you might find interesting: Steve Koonan speech to the GWPF in November of 2021. A data-rich presentation. I think you'd like it. Around minute 25 he addresses SW US droughts and specifically mentions the impact on the Anasazi Indians circa 1100.
You might also like the 4-hour climate conversation between Lex Fridman, Bjorn Lomborg and Andrew Revkin. It's episode #339. Absolutely worth the 4 hours.
Useful to contemplate how we are allocating our resources versus building resilience, and how the west is allocating resources, toward CO2 reduction specifically, that are unlikely to have a meaningful long-term impact. Meanwhile, there are plenty of other immediate impact problems that we can solve with significantly less money. E. G. Tuberculosis.
As you note, we live in a ever-changing world. We also live in a world of limited resources. Over focusing on one issue by definition means under focusing on others. Thanks for all you do!
Thanks, Nolan, I just found that speech and will check it out. Not sure I can handle a 4 hour podcast though!
Edit: less anxious about "anthropogenic" climate change.
To me parts of town where the paint is chipping, sidewalks are cracked, fences are saggy, and grass is abundantly tall appear to be islands of change in a sea of stability. But when you look at the rich parts of town you realize that the trimmed grass, fancy fencing, recoated buildings, and smooth sidewalks are really just the illusion of stability that requires huge amounts of energy to maintain.
This is true and yet the way change is framed is as important as the change itself. I find myself in the very awkward position of disagreeing with Chris on a couple of points. Most natural climatic cycles don't cause chaos everywhere without a moment’s notice. Much of what paleoanthropology is coming to grips with is the fact that using ice core samples in Greenland, for example, allows us to understand an average state of climate but that it shouldn't be used as a proxy for every ecosystem. As they gather more samples, anthropologists are realizing that entire regions were often unaffected by seemingly large climatic events. This is causing evolutionary anthropologists to reconsider certain assumptions about human evolution.
My point is just because glacial sheets expand doesn't mean its mass chaos everywhere. One reason is the rate of change. If you look at the glacier/interglacial figure, the high interglacial peaks to low glacial peaks are usually 50k to 25k years apart. There's no doubt this causes massive change, but the consequences exponentially amplify if these peaks and valleys were to occur in 2k or 5k year increments. I've been thinking about how we perceive time on geological and evolutionary scales and how creating narrative around scales results in the discounting of time (I think it will be the first episode topic of my podcast).
Really the biggest point I have to make is when it comes to the Toba eruption and its effect on humans. I'm surprised that this hypothesis is still so popular. I know the likes of Randall Carlson and Graham Hancock continue to push it but in 2022 none of the evidence supports it. Paleoanthropologist John Hawks has a great blog discussing this topic https://johnhawks.net/weblog/the-so-called-toba-bottleneck-didnt-happen/
I won't go on about it too much other than to say that the cooling event that Toba supposedly triggered appears to have already begun before the eruption, the supposed population crash is now closer to 50 kya and is due to the out of Africa migration bottleneck rather than a population crash. The foundation of the hypothesis is based on early models that were constructed in 1992. With more current data the impact of the Toba eruption, on humans and most other ecosystems, appears to be minimal.
When I think about the Toba eruption one thing that always comes to mind is Sumatran orangutans. These apes have called this region home for millions of years. When evolutionary anthropologist Herman Pontzer compared the metabolisms of all the great apes, he found that orangutans had, by far, the lowest metabolism (with humans having the highest.) In fact, the orangutan metabolism is so low that its closest comparison is to that of the sloth. I find it hard to believe that if Sumatran orangutans (or Bornean orangutans for that matter) survived the wrath of Toba, and right on its doorstep, it would still somehow devastate Homo sapiens over 3,400 miles away in Africa. Yes, a layer of ash from the Toba eruption exists across much of the earth but that doesn't say anything about the effect, or lack thereof.
I'm out of my depth in all these areas, but wouldn't genetic sequencing make it possible to establish whether there was a population crash or not?
The link to John Hawks' blog (above) will do a better job of laying out specific arguments against the Toba hypothesis. Nonetheless, I'll address it from a more basic standpoint.
Direct sequencing is near impossible. The oldest human DNA comes from the Atapuerca cave in Spain. This very early Neanderthal DNA is about 430,000 years old. The record for the oldest ancient DNA to be sequenced, of any type, was recently broken. This environmental DNA (think of DNA embedded in cores of soil) was used to reconstruct a 2 million year old Greenland ecosystem.
https://www.nature.com/articles/nature17405
https://www.nature.com/articles/s41586-022-05453-y
Quite old DNA (120-30 thousand years ago) has been sequenced from both fossil remains and soil in regions like the Altai mountains of Russia (Neanderthals/Denisovans), and the Bacho Kiro cave of Bulgaria (Neanderthals/sapiens).
https://www.pnas.org/doi/full/10.1073/pnas.2004944117
Unfortunately DNA rapidly degrades in hot and/or humid regions such as Africa, the Levant, etc. The oldest African DNA sequenced is only about 20,000 years old. Because of this, population size and migrations is mostly inferred through genetic sequencing of current populations.
https://www.nature.com/articles/s41586-022-04430-9
The various arguments of the Toba hypothesis don't really line up with much of the available evidence. Different versions make slightly different assertions. For example, one argument states that about the time of eruption Homo sapiens, as a species, experienced a bottleneck and between 2,000 and 10,000 individuals survived. This argument can immediately be discarded as this argued size was already within the known range of human populations. Genomic analysis indicates that our ancestral lineage, up to 1.2 million years ago, was always a very small population with no more than ~18,500 sexually mature individuals. https://www.pnas.org/doi/full/10.1073/pnas.0909000107
And the paper that analyzes the genomes of ancient Africans (linked above) also shows an estimated range of ~2,000 to 18,000 (but shows it is likely on the higher end of the spectrum). When dealing with our species as a whole, our population was already small.
However, this population size of 1,000-2,000 probably didn't come out of thin air. Using the Tibetan ancestral lineage as an example, you can kind of guess where they got this number and argument. The out-of-Africa bottleneck has been known to have occurred sometime between 100k years ago and 50k years ago. Most current research seems to point to sometime after 65k years ago. The ancestral Tibetan lineage experienced two bottlenecks. The first being the initial out of Africa bottleneck that all Eurasians experienced. One estimate has this migrating population at only about 1,860 sexually mature individuals. About 50k years ago this Eurasian population split into ancient Europeans and Asians (the ancient European branch appears to have gone extinct). After the split, the Asian branch appears to consist of about 1,000 sexually mature individuals and would go on to reach an equilibrium of about 7,000.
https://www.pnas.org/doi/full/10.1073/pnas.2020803118
With all this genetic information, which has nothing to do with the Toba eruption, it appears to me that the proponents of the Toba eruption are trying to shoehorn the theory into a narrative where the eruption is the cause of already occurring population dynamics. There was probably never a population "collapse" within Africa. If this was the case, African genetic diversity would be much reduced. Instead, genetic anthropologists, paleo-geneticists, and population geneticists see that as populations moved away from Africa, (I.E. Africa -> the Levant -> Asia/Europe -> North America -> South America) genetic diversity reduces. This is a result of continuous bottlenecks and new founding populations migrating into distant regions.
I've mostly read these research papers for other purposes, but after having read them and seeing the Toba argument I feel the need to push back because the data doesn't really support it. Especially when it's someone like Graham Hancock and Randall Carlson who are front facing towards the general population and are keeping these ideas alive. When you throw in archeological evidence and climate data it makes the argument even weaker.
With DNA and climate analysis technology improving exponentially every year, concrete answers to many questions are likely to emerge.
Thanks very much.
"African genetic diversity would be much reduced"
Powerful argument, since it's pretty diverse.
It's been a few years since I read David Reich's "Who we are & how we got here", in which he invokes a current "ancient-DNA revolution" that now makes it possible to use far more recent DNA to interpret past events.
For example, apparently this Eurasian population you mention split, with one group headed west (basically us Europeans) & the other east. He says that this explains why Europeans are more closely related genetically to Amerindians than to East Asians since it was a different population that spread into East Asia & stayed there, while the eastward post-split migration of the Eurasians basically headed across into the Americas.
Reich also says, for what it's worth, that they've discovered a small area buried deep within the anterior skull where you might find DNA that has lasted while everything else has degraded. All you have to do is find that part of a skull...
So I was thinking that if you looked at the DNA, even today, of various populations around the world, then considered Youngest Toba eruption (74,000 years ago) and calculated Who-Where would be most severely affected by it immediately, & Who-Where might have best ridden out its affects over the long term, you could assess the validity of the hypothesis that way. Am well aware that this wouldn't be an easy thing to do but it might be a way for proponents of the Toba catastrophe hypothesis to test it.
Reich certainly makes it sound as if there's been a great deal they could divine in recent decades that had been simply inaccessible previously.
There's no doubt that advanced computation is allowing recent DNA to provide more predictive value. But its also true that improved DNA sequencing is really driving the explosion of data in ancient DNA and especially environmental DNA. I've come across studies where stretches of ancient DNA as small as 35 base pairs in length are reconstructed into a single genome. That's insanely small! Imagine the ease of putting a 100 piece puzzle together. Now imagine putting a 10,000 piece puzzle together.
The petrous bone does seem to conserve DNA more than other bones. Reich's lab was actually criticized when the amount of these bones, which his lab destroyed
trying to sequence DNA, became public. Part of the criticism was the fact that if you destroy specimens now you won't be able to apply advanced technology to them in the future. It's a common practice of geneticists and even paleoanthropologists to leave some portions of a dig/specimen intact in order to give future generations a better chance of securing DNA or dates from dig sites.
When it comes to ancient, or fossilized remains, any DNA that can be obtained has already been sequenced. In fact, most of the sequenced DNA is available to the public and can be analyzed using online tools such as the NCBI online tool https://blast.ncbi.nlm.nih.gov/Blast.cgi
The great thing about having all this DNA available in a database is the fact that it can be mined for secondary uses. There's a ton of information on so many species: Mammoth, mastodon, Homo sapiens, Neanderthals, Denisovans, and countless other plants and animals. There are signals in the data for ecosystem collapses and extinctions but none that match near the ~74 kya Toba eruption. For instance, there are probably dozens of papers that document a collapse in population of eastern Neanderthals (a region that was already one of the coldest occupied by hominins). But this occurred 120-100 kya. The data even shows that a group of European Neanderthals migrated east and eventually took over the areas formerly occupied.
www.pnas.org/cgi/doi/10.1073/pnas.2004944117
Using environmental DNA sequencing another study basically documents the last stand of the woolly mammoth in the Siberian Tundra. As the ecosystem changed from an open grassland to woodland the mammoths appeared to cling to the grassland until it too disappeared, and they with it, about 4,000 years ago.
https://doi.org/10.1038/s41586-021-04016-x
The data from all this DNA sequencing is deep. But it fails to show anything that specifically aligns with the Toba Eruption.
Yes, it's natural enough, I guess, that people interested in X then discover Y, & say "Bingo! X+Y = Z". It reminds me of the hypothesis that the Chicxulub asteroid caused dinosaur extinction. Does seem pretty convincing. But there remain geologists who doggedly favour the Deccan Traps as the cause.
All this is fine provided everybody can keep ego out of the discussion.
Absolutely! I think it also matters in which order something is learned. I've casually read a science article, that I have no particular opinion on, and when reading a second article (on the same subject/announcement) I've found myself almost unconsciously disagreeing with the second article because it didn't agree with the first. Then I think to myself "So, if I would have read the second article first I would be disagreeing with the initial articles points?" And this happens on topics that I have no particular opinion or attachment towards. What happens when it's on a subject that you have actually invested time and resources in? I think this is a big driver of science that we are all mostly blind to. It's also why it seems to take the next generation to reconsider such theories and assumptions.
Wow. Thank you for this. A question I've always had is around this concept of how many individuals were in a given bottleneck population. When you write, "about 1,000 sexually mature individuals," do you mean that the DNA of around 1,000 people is detectable in downstream genetic information? In which case, it's not that there were 1,000 people, but that only 1,000 people had offspring whose offspring survived and so on down the centuries? Otherwise, how do we know how many people were alive and DID NOT have offspring who carried their DNA into the distant future? I find this confusing.
I'm also confused by the notion that human population levels were as low as 18,000 people a million years ago. Why would the population be that low in Africa, when even today, when much of the continent is uninhabitable for any primates other than humans, there are far more chimps alive (estimates range from 200k to 300k). Such a low base population of early humans seems counter-intuitive to me. Maybe you can help me see this better.
Lastly, WHO ARE YOU? Are you a geneticist? You are obviously very well-versed in this stuff. I'd love to know more about your background, if you are willing to share.
Hey Chris,
I am definitely not a geneticist although I work very hard to understand ancient DNA. I just find human origins fascinating and currently research it as a hobby. After high school I joined the Air Force and became a radio frequency/signals communication technician. After four years I left the AF and that's still my day job in the civilian world.
In 2016, I decided to get a BA in evolutionary anthropology which I finished in 2020. My undergrad thesis was on the evolution of running, which was an absurdly broad topic and a terrible choice as a thesis topic. But in the long run, it was the best choice I could have made as each section was an introduction into what we currently know about the different aspects of human evolution. Brain growth/organization, energetics of bipedal walking, the reduction of body hair, sweat gland emergence, dietary shifts, etc. I've been going down these different rabbit holes for the last five years or so.
The last two years I noticed how ancient DNA and environmental DNA research was exploding so I went back to school and got a certificate in Computational Life Sciences. I completed that earlier this year. I'm definitely not an expert but just someone trying to understand this stuff enough to figure out what the hell happened in our ancestral lineage. With that being said I've probably learned more by wading through studies and having my mind blown by the information that I find. The plan is to apply to grad school this year. But either way I'll still be learning on my own. I tell myself I am researching to incorporate what I learn into writings or YouTube videos but find that researching is too fun to stop and create a finished product. I have managed to create some mediocre videos. This one on the Denisovans is relevant to the discussion we are having.
https://youtu.be/1kW0Ezo2fu8
(Notice how I hypocritically indicate an out of Africa migration at 70 kya. I am planning a whole series on out of Africa migrations where that will be updated.)
I also maintain a blog that is mostly just random ponderings on human evolution dawnofsapiens.com
I actually think that understanding population size is one of the hardest aspects of genomic analysis. Math has never really been a strong point, but it is still interesting to see how it is done. Researchers aren't actually detecting individual genomes downstream. They pick different aspects of DNA to run different analyses. If I'm really trying to understand I'm likely to read a section 10 times before I even begin to grasp what the research is getting at. For example, in the paper that predicted an effective population size of 18,500 individuals, https://www.pnas.org/doi/full/10.1073/pnas.0909000107 they use rare events known as Alu insertions. By measuring the length of the haplogroup that an insertion resides on they can determine genetic diversity and population size. Another way of measuring is by dividing the genetic diversity of a population by four times the average mutation rate.
These calculations get very convoluted and to be honest, even when using freely available online computational tools you don't really need to understand the algorithms. Just input the variables and wait for the results. At some point I'd like to ask a geneticist, such as John Hawks, to explain effective population predictions.
I should add that effective population only determines the average breeding pairs of a population. For a group like the San (according to information that I've read) 1/3 of the population is adults, 1/3 is children, and 1/3 is elderly (it's not that unbelievable). So, in this case the effective population size would more than likely predict only about 1/3 of the actual population size (depending on how you treat elderly males). Even accounting for this 1/3rd prediction, effective population can sometimes become nonlinear with absolute population. It's not a perfect measurement for absolute population size but so far it's what I have seen used in the academic literature. It can at least be used to make relative comparisons among different populations or species.
Your point of unaccounted for individuals is well taken. There are several hints of archaic Homo sapiens groups that are unaccounted for in such genetic analyses. For instance, the skull of a Homo sapiens individual was found in Greece and dated to about 210 kya. This individual, and likely others, left Africa well before the more well-known out of Africa migration. How many were in this group? And how many other such groups existed that aren't recorded in our genomes? It's hard to tell. On the other hand, even some previously unknown branches would be captured by genomic analysis.
For example, in 2021 a paper was released that analyzed several individuals from the Bacho Kiro cave in Bulgaria. They were dated to ~45 kya. When they analyzed their genomes, they found that they were, surprisingly, more closely related to East Asians and Native Americans, than to modern day Europeans. Other remains in the area that are dated to about ~40 kya are related to modern day Europeans. This indicates that the ancestral East Asian population split at least 45 kya and one group continued to East Asia while the other turned toward Europe. This European branch went extinct. But a genomic analysis of the population before the split would have still accounted for the European bound individuals.
https://www.nature.com/articles/s41586-021-03335-3
I think most population figures given are on the low side. But everything I've seen does seem to indicate that hominins were a relatively small population, overall, when compared to other species.
Several points come to mind as to why this might be the case. Both are ecological in nature. One, with the number of bipedal species we are learning existed alongside Homo sapiens (and especially early Homo sapiens) we should consider the niches they fill as well. This isn't the sexy argument of human agency where humans go to war with other bipedal species and push them out, but I think not viewing our species as integrated in their environment is a mistake.
The anatomy of the different species offers clues to their niches. For example, Homo naledi is dated to about 230 kya in South Africa. They are well suited to bipedal locomotion and yet they retained longer arms and curved fingers for climbing. To me this indicates they inhabited more wooded areas of Africa (similar to the habitat of our ancestors the australopithecines). It appears that Homo erectus, or its derivative Homo heidelbergensis, was also still kicking in the early years of Homo sapiens. They would have kept our ancestors from expanding to an extent.
But what I've really been thinking about lately is the influence of the environment itself. This is the most overlooked and ignored aspect of humans, both today and in the past. Moving into open territory would have exposed our ancestors to predators. This likely had an effect on population. But the most important factor that shaped human beings and their ancestors is the change in density of food in savanna environments.
I’ve conducted some preliminary research on savannah chimpanzees and am amazed at how a change of environment shapes the behavior and demography of the species. For example, the population size reduces dramatically to an average of 29 individuals compared to 90 individuals for forest chimpanzees. During an online lecture I asked a primatologist about the difference in behavior of forest chimps versus savannah chimps when two groups meet at the edge of territory borders. She stated that because savannah chimps require such large territories, to support even small groups, that they rarely encounter other populations. But even when they do run into each other violence is rare and dominance displays are usually as far as things escalate.
https://doi.org/10.1016/j.jhevol.2021.103137
The open savannah requires much more physical activity to survive. Chimpanzees are much less active. I would argue that high activity levels reduced fertility. Evolutionary Anthropologist Herman Pontzer’s work has showed that the Hadza (and many other physically active populations) have sex hormone levels that are up to 30% less than industrialized populations. These are healthy individuals but their metabolism goes elsewhere and this likely results in less babies. In the book Nisa: The Life and Words of a !Kung Woman, Nisa points out that sex in San populations rarely resulted in pregnancy. Different environments may change the results but then again Neanderthals and Denisovans appeared to have even smaller group and population sizes. Even human groups that live in rainforests such as the Piraha and African Pygmies don’t really see expanded populations. They even have reduced life spans where 45 years really is old.
https://doi.org/10.1371/journal.pone.0270221
http://dx.doi.org/10.1073/pnas.0708024105
It seems that I have written a book here…
By the way, I reached out to Professor Alan Rogers, who is a coauthor of
one of the papers I linked to earlier. I asked if he could point to something that broadly explains the science of population inference through DNA. He directed me to this tutorial he made for one of his classes https://arxiv.org/pdf/2201.02668.pdf
So far I've only briefly skimmed it but it looks like it does a pretty good job of laying the science out.
Brilliantly put point. It's always good to be reminded of the instability of this world. Buddhism is always doing that, because it's only when you wish/hope/believe that this life is anything other than unstable and difficult, that you get into REAL trouble.
Just a tiny revision for anybody who searched for "Apocalyptic Earth: Field Guide to the Future of the Earth" & couldn't find it. I found it under the name "Apocalyptic Planet: ...". I'm sure most would have just searched the authers name & found it anyway but just in case. Thanks for another great, thought provoking read Chris.
Fuck. Thanks. I'll edit that.
Great article! Video is pretty good, too.
When it comes to things being fine or stable, it depends on the perspective one takes. It is very unlikely that a rapid planetary change would happen within persons lifetime. So things are usually stable from that point of view - and fine. When the shit hits the fan, life becomes a struggle, people need to rely on each other and life becomes charged with meaning - which is fine too. In both cases one could overly concentrate on finding the negative, but I don’t think it does any good and may even hinder people living a life of fullfilment and harmony with nature and fellow humans. Even rocks start to look like liquid if you consider wide enough time frame. Choose the outlook that serves you the best, focus on the moment and enjoy the ride.
I say this every time people start freaking about the climate. Nothing in this life lasts forever.
Yes. I find it both profoundly sad and beautiful at the same time, both scary and comforting. It’s an acknowledgement which demands us to dive deep into the human experience. Every time I find myself wasting time doing meaningless things in front of a screen, I feel like I’m betraying it. It’s a time to make some changes.
This is great - I really appreciated hearing the Charlie Zender ep too!
Please forgive me for this, but it’s a bugbear of mine about climactic/climatic. ‘Climactic’ refers to ‘climax’, whereas ‘climatic’ refers to the climate. Although the idea of an extra-ordinary climactic situation sounds quite... exciting, no? Anyway, as a fellow word lover, I’m hoping you’ll take this as in the positive spirit intended; I do not actively want to be a dick 🤪
"Forgive you?" I thank you! That's a significant error. Many thanks, Jon.
Your writing is so good. Bastard.
Craig Childs' writing is beautiful -- I've read The Way Out and The Secret Knowledge of Water, both outstanding, intimate portraits of desert exploration and the ways of water in the arid Southwest.
According to this website "https://www.theworldcounts.com/stories/how-many-babies-are-born-each-day" which shows the number of births on the planet each day clocking over in real time at an absolutely ridiculous rate of knots, we need approximately 1.79 planet Earths to provide adequate resources & absorb our waste. I'm not sure how they calculate that but if true would indicate the ideal maximum human population would be not much more than half the current number. Try telling that to everyone who believes "there's no overpopulation, the entire human population could comfortably live in the state of Texas alone"
I think in reality it is a bit more complicated than that. In many developed countries population growth has plateaud. Educated women are having fewer children because they don’t need that support around them. Some even think that we might be hitting the peak population at the moment, since in countries like India and China people are moving more and more to the cities and joining the workforce, thus earning a decent living and not necessary needing children. The absence of the old thriving village communities has already increased the ”greening” of the rural areas in those countries. Nature takes back the vacant lands. If you look at the places where there is most war and most health issues, you see that in those places people also are having more children.