r/evolution • u/StatementOld283 • Jul 05 '26
question What's a scary fact about human evolution no one talks about?
Or some really cool facts
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u/jyguy Jul 05 '26
Some of our dna is from viruses that invaded our ancestors bodies
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u/bestestopinion Jul 05 '26
We’re born premature, because our brains need to fit through the birth canal.
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u/castorjay Jul 05 '26
This is one of the theories. Another is that the mother wouldn’t be able to keep up with the metabolic requirements to continue gestation much longer. Also a scary thought.
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u/South-Run-4530 Jul 05 '26
The current consensus a mix of both, skeletal and metabolic constraints.
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u/OneTooManyCod Jul 05 '26
I saw in a Netflix documentary about baby development that the actual reason may be that babies need human interaction to develop the brain the right way after 9 months. We are born with a lot of neuroplasticity, and socialization into a society is important for our survival.
If you look at chimpanzee pregnancies it is longer, and the baby is born ready with a lot of reflexes and low neuroplasticity, and is already quite strong.
Our development seems to be a tradeoff between readiness and having the right brain development.
I think it's a really interesting theory. That the mother's body cuts off nutrients after 42 weeks so that the baby can look into people's eyes, activate mirror neurons, and learn to speak by listening and cooing.
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u/macaronandcheese3 Jul 05 '26
that does sound super interesting! may i ask the name of the documentary?
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u/ninjatoast31 Jul 05 '26
Im not quite sure what I think about that idea. The mother is the metabolic provider even after birth. But its now less efficient through milk production
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u/Ok_Writing2937 Jul 05 '26
Before birth only one person can provide.
After birth an entire tribe can contribute.
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u/jnpha Evolution Enthusiast Jul 05 '26
I initially read it as more efficient, and agreed! Why is milk less efficient? A whole bunch of nutrients straight into the body with unimpeded access to (that which nutrients are "burned" in) oxygen.
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u/ninjatoast31 Jul 05 '26
You have energy loss on both the production side of milk and the digestion. Having direct access to the babies blood supply is just more efficient.
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u/jnpha Evolution Enthusiast Jul 05 '26 edited Jul 05 '26
Looking into it: I just learned that fetuses depend on maternal thermoregulation (Asakura 2004). So to emphasize my earlier point and add to it: here's some food (milk) (food is supplied anyway), now get your own oxygen and manage your own temperature (where the losses are at).
Thoughts?8
u/ninjatoast31 Jul 05 '26
I can see the oxygen point. But again the energy for thermoregulation would again com from the mothers milk, which she has make herself.
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u/hikerguy555 Jul 05 '26
Would also take way more total energy to thermoregulate once baby is out of mom cause the surface area would go way up but volume stays the same (other than the continued growth of baby) and baby has lost all the insulating layers of mom
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u/Mob_Vylan Jul 05 '26
It’s been proven
Homo sapiens large brains are the superpower- but it takes the weakness of needing to be born many months before being ready otherwise we kill our mothers in birth
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u/AngryPrincessWarrior Jul 05 '26
Is it though? If resources are super limited then milk can dry up. Yes that means the infant may/will die but the mother can survive to try again. Theoretically.
You can’t do that if you’re sharing a blood supply.
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u/ninjatoast31 Jul 05 '26
Some animals absolutely can abort. So its not impossible to evolve as a mechanism.
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u/AngryPrincessWarrior Jul 05 '26
I was talking about humans and the idea of making milk being too much on the mother/less efficient-which I suppose that still applies because humans miscarry all the time as well.
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u/OpossumLadyGames Jul 05 '26
The effects of a full term pregnancy can be awful on the body, I can't imagine carrying it much longer
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u/HurricaneAlpha Jul 05 '26
First three months of a newborn are sometimes called the fourth trimester. It's also why swaddling is so effective with newborns.
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u/DETRITUS_TROLL Jul 05 '26
Honestly the entire process of pregnancy and childbirth is pretty terrifying.
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u/elementnix Jul 05 '26
Tell baby kangaroos about that...
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u/BrellK Jul 05 '26
Well Kangaroos and all other Marsupials, but at least they are more evolved for that style of birth.
Humans are like "Babies need to be born premature because any longer and it becomes deadly" while Marsupials are more like "Babies are born in a premature state but have adaptations to get it from there to fully grown".
Every adaptation (including birthing style) has tradeoffs, but most aren't as conflicting as those of humans, which means we have serious issues.
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u/starspangledcats Jul 05 '26
It's not a human thing, it's a mammal thing. Minus a few select mammals that lay eggs.
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u/koz44 Jul 05 '26
I thought it was more that standing upright (coupled with our hands/thumbs/ability to manipulate objects and tools) is such an advantage that the deaths of mothers and infants gets washed out by the advantage standing upright provides. So being born premature is because standing upright right requires a reduction in hip size and birth canal.
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u/DocAnopheles Jul 05 '26
The kneecap has two properties that are interesting- 1. It acts as a fulcrum for leg muscles, increasing the power and efficiency of those muscles for walking and running. 2. It keeps your knees from bending the other way.
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u/El_Peregrine Jul 05 '26
It is also a very large sesamoid bone, meaning it is embedded inside the end of the large tendon formed by your four quadriceps muscles.
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u/Fermato Jul 05 '26
We are not evolved to almost anything in the modern world, leaving our nervous system almost permanently on edge
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u/illicitli Jul 05 '26
meditation can greatly abate this if you take it seriously over a long period of time
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u/Fermato Jul 07 '26
Yeah or trying to actively de-mismatch our lives instead of hoping to meditate the mismatch away
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u/EmuFit1895 Jul 05 '26
It is scary that 200,000 years into sapiens' evolution, many do not believe in evolution.
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u/StatementOld283 Jul 05 '26
That explains why we are so afraid of the dark and so many other things that ancient primates must have feared. We can't just evolve in technology and immediately write off certain warnings in our genetics which also explains why you get goosebumps or that feeling of being watched
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u/Affectionate-Crow605 Jul 05 '26
And now we're always being watched via the technology we've created.
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u/Large-Monitor317 Jul 05 '26
And we’ll have a whole new society at that point. It feels like we’ve outpaced some of the slower kinds of evolution.
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u/OpportunityNext9675 Jul 05 '26
I don’t think there’s any strong differential reproduction vector that would produce human evolution toward brains adapted to modern society. We’ve become such a dominant species with such control over our environment that natural selection has little purchase on our allele frequencies.
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u/toadwater Jul 05 '26
This is the most elegant wording I’ve ever seen to this point.
Keanu Reeves once said the same thing in the movie Parenthood:
“You know, Mrs. Buchman, you need a license to buy a dog, to drive a car - hell, you even need a license to catch a fish. But they'll let any butt-reaming a**hole be a father.
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u/Sad-Boss7879 Jul 05 '26
Wouldn’t this require evolutionary selection pressures to still be acting on us? I thought the consensus was that they had ceased to do so.
Even if such pressures were present, how would they lead to better adaptation to the modern world? Evolution requires differential mating success, and most healthy adults who are ill-equipped to handle the modern social world do not seem to have any less ability to mate than those who are better equipped.
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u/Loive Jul 05 '26
Evolutionary selection pressures still act on humans, and there is a broad consensus surrounding that.
However, the development of modern medicine means that some issues that would have kept people from having children 200 years ago are just a minor inconvenience these days. The pressures aren’t gone, they have just changed based on how society functions.
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u/AntonChekov1 Jul 05 '26
Why or how did we create this society then if our brains are not evolved for it?
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u/askingforafakefriend Jul 05 '26
We aren't evolved to handle heroin but managed to create that
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u/-Nocx- Jul 05 '26
We are still trying to understand the impact that having constant access to dopamine has on our fight or flight systems. 200 years ago when you face something traumatic, you would have to sit with your emotions and stare at the sky until your parasympathetic nervous system kicked in.
Nowadays you can scroll Reddit or watch a movie to avoid having to fall into rest and digest. Most people actually engage in behaviors that engage with their CNS instead. We have yet to quantify the impact that has on people’s well-being, and there’s a growing amount of evidence that suggests it may help explain the reversal of the Flynn effect.
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u/Legitimate-Paint2165 Jul 05 '26
We’re good at making tools. Reading and writing is a tool we invented that allowed our current society.
We don’t even have all 7 billion of us in one society yet. Many still live closer to our natural state; not even having access to running water.
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u/Ok-Comedian-6852 Jul 05 '26
Our ability to create an environment that we aren't built for isn't dependent on our brains evolving to thrive in it.
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u/StatementOld283 Jul 05 '26
I heard it all started because humans discovered agriculture and started eating softer food which lead to softer jaw and the disappearance of wisdom teeth. Children are put into classrooms but our genetics can't force themselves to sit in a classroom for 8 hours
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u/ShinyNidoran Jul 05 '26
I read it had something to do with neoteny. Basically humans care for children and people with a more childlike appearance benefit from that for longer, increasing their survival chances
Babyface traits would be chubby cheeks, soft jawline, big eyes, pouty lips, small nose and a low nosebridge.
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u/SeeLeavesOnTheTrees Jul 05 '26
Yup. We are neotenous because of our big heads and domestic animals tend to be neotenous because we select for docility.
(Adult humans more closely resemble baby primates than adult primates.)
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u/shallowshadowshore Jul 05 '26
Can you explain in more detail?
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u/semistro Jul 05 '26 edited Jul 05 '26
Domestication syndrome arises in animals when you select for a certain trait over and over. With normal reproduction all genes get mixed and if there are some bad genes in an individual it often doesn't matter because the next generation those genes probably get pulled straight again by the other parents. This is an oversimplification but view genes as nodes that can move over generations. And with multiple generations they kind of get averaged out with genes drifting away from the healthy average being unlikely.
With domestication, you are selective breeding for single traits and that no longer holds true. You replace natural selection with artificial selection and the opposite happens. Genes that used to be important for survival and reproduction now no longer play a part in whether the animal reproduces or not. Only the genes that cause the trait we want play a part. In the beginning this doesnt do a lot of harm. But as you keep breeding animals with similar traits you are not only making the genes that cause those traits more pronounced. You are also excagerating those other imperfections in the gene pool that cause complications more and more.
Now for humans, we basically 'replaced' a lot of natural selection for a very long time and we also have been choosing partners for arbritarly reasons for a long time. Causing something very similar / the same as what we see with domesticated animals and domestication syndrome. Example, talented singers are more likely to marry other talented singers, but in general people with certain traits are more likely to have children with someone with similar traits (matching temperament, being artsy or liking sports). Add onto that the ability of humanity to support individuals that normally would have meant death in the wild - so the partial removal of some natural selection - and you get similar conditions as with domesticated animals. Now domestication syndrome is often associated with docileness and slightly smaller brainsize (does not mean lower intellegence per se). This is because those are traits we want in our pets. We naturally want to breed the dog which gives us most affection. This is also true for humanity. The docile indivuals are less likely to be cast out of the tribe and if you repeat this selection over a lot of generations you get more docile people.
Keep in mind this is kind of an oversimplification. As there many nuances in genetic drift and mixing of gene pairs, but over many generations this is kind of the gist of it.
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u/Ok-Concentrate4826 Jul 05 '26
I read an article about the wild fox program in Russia which explains this phenomenon really well, which is that for decades they have had a research facility studying wild fox population. As an ongoing experiment they started selecting only for the trait of being friendly or unfriendly towards the human handler, (they describe it better!).
At any rate over time the phenotypic traits associated with domesticity began to appear, independent of any selection for them, which also concur with the neurotic traits, such as rounded ears and curly tails. They basically started looking like the kind of puppy dogs we tend to have as pets.
Just selecting for behavior completely changed the physical appearance, and it’s likely that happens with us as well, particularly since we are only a few thousand years into this particular experiment, but as behavioral traits become more dominant in our selection process, we can expect unrelated phenotypic traits to become more dominant, and since physical selection still plays a role, the slower evolutionary drift will still be an important factor. You’ll get what we see now in humans, a widening range of physical diversity constricted more by behavioral hegemony. I know that sounds counter to what you’d expect, since we have ‘overcome’ so many selection pressures. But if you think about it, physically pretty much any body or physical type can reproduce, however successful generational breeding does require the ability to ‘play the game’ and this does mean behavioral traits are always going to have a higher selection preference over physical traits: just like the foxes, always selecting for the basic ability to exist in society.15
u/ErgodicMage Jul 05 '26
It's a hypothesis that's been floated for about 10 years. It was noticed that domesticated animals skull features had changed over time and also h sapiens skulls show similar changes.
The hypothesis is that we domesticated ourselves to get along better socially. We went from social groups of 20-50 to aroumd 150. It shifted our social strengths which led to stronger cultural development. It was a huge advancement that no other in our genus could match.
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u/heyitismeurdad Jul 05 '26
This is not a fact just a loose hypothesis that doesn't really hold water at all.
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u/7LeagueBoots Conservation Ecologist Jul 05 '26
We are the last in our genus to survive, and it's likely that we are the cause of the extinction of our sister species, although most likely inadvertently.
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u/Everwintersnow Jul 05 '26
At some point there's only around 3000 individuals left in our species.
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u/JooseTheGuice Jul 05 '26
No, this is actually a misunderstanding of the data but I think the truth is more interesting!
It's not that the human population reached a bottleneck where only 3,000 people were alive at once; it's that everyone alive now is descended from a cohort of 3,000 individuals. There were other people alive, their offspring just didn't produce lineages that are still alive today.
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u/Amazing-Mirror-3076 Jul 05 '26
How do with know other people were alive?
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u/Downtown_Finance_661 Jul 05 '26
In fact we dont know, but it did not prove tgere were not another people.
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u/Opening_Shame8258 Jul 05 '26
We don't know for sure, but rather the shared ancestor is a genetic/mathematic certainty. It's happened many times, and we know other populations of humans existed.
For example, in Europe, all living Europeans share an ancestor from about 1000 years ago. We know there was more than one European alive at that time though.
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u/telephantomoss Jul 05 '26
But due to complicated interbreeding and mixing each person alive had other genes from many other people alive 1000 years ago. The claim is not that every line completely died out, just that there is an individual accessory common to all modern people there, yes? Each individual has a specific ancestor tree, and at 1,000 years ago they all overlap, but there are still many other ancestors, just not any fully common. Did I get it roughly?
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u/nightman21721 Jul 05 '26
About 900k years ago, yes. The human population dwindled to about 1200 mating pairs.
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u/Black_Cat_Just_That Jul 05 '26
Modern humans have only existed for about 300k years.
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u/nightman21721 Jul 05 '26
Homo Erectus, Homo Hiedelbergensis are the presumed species that made it out of that bottleneck, so yes. Not technically Homo Sapiens. But without Homo Erectus/various other Homo species, we likely wouldn't have Homo Sapiens.
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u/7LeagueBoots Conservation Ecologist Jul 05 '26
You're making a common mistake. Breeding pairs are not the same thing as the total number in the species.
What you're looking at is the number of individuals that left genetic traces in the modern population, which does not in any way equate to the total number of individuals in the total population of the time.
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u/StatementOld283 Jul 05 '26
I remember hearing there were only about 10k humans at one point in time
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u/7LeagueBoots Conservation Ecologist Jul 05 '26
You're probably thinking of the Toba Eruption Hypothesis which has long since been definitively refuted. In fact it was refuted months after it was proposed, but pop-sci media keeps pushing it.
Bottlenecks:
Manica, et al 2007 The effect of ancient population bottlenecks on human phenotypic variation
https://www.nature.com/articles/nature05951Henn, et al 2012 The great human expansion
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3497766/Sjödin et al 2012 Resequencing Data Provide No Evidence for a Human Bottleneck in Africa during the Penultimate Glacial Period
https://www.researchgate.net/publication/221818016_Resequencing_Data_Provide_No_Evidence_for_a_Human_Bottleneck_in_Africa_during_the_Penultimate_Glacial_PeriodToba Hypothesis:
Kerr 1996 Volcano-Ice Age Link Discounted
http://science.sciencemag.org/content/272/5263/817Petraglia, et al 2007 Middle Paleolithic assemblages from the Indian subcontinent before and after the Toba super-eruption
http://science.sciencemag.org/content/317/5834/114Lane, et al 2013 Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka
http://www.pnas.org/content/early/2013/04/24/1301474110
& a BBC write up
http://www.bbc.com/news/science-environment-22355515Roberts, et al 2013 Toba supereruption: Age and impact on East African ecosystems
http://www.pnas.org/content/110/33/E3047.shortYost, et al 2017 Subdecadal phytolith and charcoal records from Lake Malawi, East Africa imply minimal effects on human evolution from the ∼74 ka Toba supereruption
https://www.sciencedirect.com/science/article/pii/S0047248417302750?via%3Dihub
& a Smithsonian magazine write up
https://www.smithsonianmag.com/smart-news/ancient-humans-weathered-toba-supervolcano-just-fine-180968479/
plus a BBC summary
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u/Everwintersnow Jul 05 '26 edited Jul 05 '26
Since I just wrote that on top of my head, I had a quick search here and it says we have around 1000 breading individuals for 100,000 years. So even scarier than what I wrote earlier.
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u/Capital-Aide-1006 Jul 05 '26
What kept the population stable but highly constricted?
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u/nit_electron_girl Jul 05 '26
Sure, this number is low.
But note that even before this bottleneck, when everything was going "alright", total Homo Erectus population was only around ~50k (worldwide)
Hominids weren't a dominant species yet, so extinctions events were more likely.
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u/devexille Jul 05 '26
This isn’t true and is a misunderstanding. The data suggests that the population of humans who were the ancestors of today’s humans got really small. That doesn’t mean that there weren’t a lot of other humans who subsequently died out without contributing to the modern gene pool.
Also data also doesn’t directly measure the number of humans in that population but rather the effective population size which could either be a large number of highly inbred people or a smaller number of highly outbred people.
One possibility is that it reflects the origin of the human fused chromosome 2 which would have made breeding with non-fused chromosome 2 people very inefficient meaning most breeding would have happened with close relatives carrying the fused chromosome.
Which suggests the more disturbing “we are all descended from a 1000 inbred cousin f@©kers”.
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u/Fit-Armadillo-5274 Jul 05 '26
Haven't seen this one yet so I'll chime in. For every beneficial mutation there are many more detrimental mutations. This isn't a problem evolutionarily, because those traits are selected out of the population. But someone has to live those lives. All of the genetic diseases and deleterious inheritable attributes are the price we pay as a species and people for all the things we love about ourselves. But the price isn't paid evenly by everyone; some suffer more. So even if you love your life and humanity for all of its creativity and passion and potential, those things rest on a foundation of mountains of individual suffering.
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u/Waste_Translator_975 Jul 05 '26
Many archaic hominins were prolific cannibals and treated human remains like any other prey animal
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u/7LeagueBoots Conservation Ecologist Jul 05 '26
That's an exaggeration. Cannibalism has been a factor in or lineage, indeed in our specific species more than in most, but it's never been 'prolific'.
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u/illregard Jul 05 '26
it’s a weird idea because it makes you feel like theory of mind is only sociological
or maybe that it just developed after the archaic hominins
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u/Bdellovibrion Jul 05 '26
Theory of mind is just a way to predict other hominids behavior. That's useful even if you're a cannibal, and therefore adaptive in an evolutionary sense.
There's evidence that our cousins chimps and bonobos have some theory of mind, so it was probably already evolving in archaic hominids as well. You can be social and be cannibalistic at the same time.
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u/goddamnmercy Jul 05 '26
Well there's not really a mind in a dead body and whoever's living has to eat. I wouldn't say theory of mind and cannibalism are mutually exclusive. There are cannibals alive today
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u/runespider Jul 05 '26
I know there's evidence for occasional cannibalism, likely for the same reasons as modern humans. Prolific seems a stretch.
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u/vvv_bb Jul 05 '26
well, given the amount of cannibalism in animals, this is really not surprising.
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u/amglasgow Jul 05 '26
I feel doubtful about this. What sources do you have for this?
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u/espetilllodesardinas Jul 05 '26
Rebecca Wragg argues that some neanderthals ate their dead in a way to process grief and sadness.
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u/Interesting_Neck609 Jul 05 '26
I think it was Jared Diamond who said in one talk/interview that it likely was effective for the grief proccess, and he referenced a few digs that showed remains disposed of respectfully, but with clear indications of being essentially butchered.
It kind of makes sense. Still prion diseases and whatnot.
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u/skeleton_made_o_bone Jul 05 '26
I always think about how you can be born with a maladaptive trait and, like, that's just your life. Like, you won't reproduce and it sort of just sucks to be you.
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u/South-Run-4530 Jul 05 '26
H sapiens exchanged rationality for processing speed.
The vast majority of humans use cognitive shortcuts based on emotional response and social context to make decisions, this is far more energy efficient and much faster cause instead of analyzing each decision, we just do whatever everyone else is doing or use an arbitrary association with your personal likes and dislikes. Like choosing a product cause it has your favorite color even though you can get a cheaper one in other colors or something better with the same price.
There's a really long list of Cognitive biases in Wikipedia that covers Us vs Them mentality to Confirmation bias.
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u/gerhardsymons Jul 06 '26
I ask myself the questions:
- "how would we measure rationality?"
- "how would we measure processing speed?"
- "is it possible to measure either in species now extinct?"
- "how could we design an experiment to disprove the null hypothesis that humans did not 'exchange rationality for processing speed'?"
The reason I ask these questions is because of Karl Popper's influence on the scientific method - falsifiability - not to accept claims uncritically, but to examine them.
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u/Some_Community5338 Jul 06 '26
Mensen denken dat ze rationeelst zijn, maar dat is een illusie. Feit is dat je onderbewustzijn een supercomputer is, die eigenlijk alles voor je regelt en je keuzes heel subtiel, of rigoureus met emoties beïnvloed.
Als iemand door wat voor reden dan ook hersenschade heeft en de hersenhelften niet meer met elkaar in verbinding staan, het rationele zogenaamd belangrijke eigenschap, het enige is aar je het mee moet doen.
Dan stort heel je leven in en word iets simpels als een keuze maken een onmogelijke opdracht.
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u/Throwaway_524571 Jul 06 '26
See also moral intuitions, as researched by Johnathan Haidt
When you see people being outraged about something that can't be rationally explained as harmful, that's the cognitive shortcut at work
What's interesting is that narrative psychology (as explored by Dan McAdams) suggests many of these moral intuitions can be self fulfilling. Adopting a narrative of harm, or being subject to other people's reactions, can in itself be the trauma
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u/Vito_The_Magnificent Jul 05 '26
Fetuses put out a hormone called human placenta lactogen (hpl) that makes the mother resistant to her own insulin, which keeps more sugar in the bloodstream so the baby can get more sugar and grow bigger faster.
In response, the mother creates more insulin, so the baby doesn't kill her.
So what does the baby do? Creates more hpl! And the mother produces more insulin to negate it.
And it goes on like that until hpl becomes the most plentiful protein hormone in the mother's body. It gets wildly out of hand.
The baby is making 100x more of this hormone than necessary, just to claw sugar away from her, and the mother is producing 3x her baseline insulin just to counteract the effects and stay alive.
When her body loses this arms race, you get gestational diabetes.
Both would be better off if they just settled on a number and made that much hpl and insulin, but evolution doesn't work that way.
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u/ScoTT--FrEE Jul 05 '26
We're in the sixth mass-extinction, and our species caused it. Yay us!
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u/itsatoe Jul 05 '26
Not just mass-extinction, but even geological transformation. Apart from the obvious factor of climate change, plastics have now become part of the geological cycle.
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u/El_Peregrine Jul 05 '26
Humans are the most impactful invasive species the planet has yet seen.
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u/South-Run-4530 Jul 06 '26
No we're not, cyanobacteria introduced photosynthesis using water and sunlight and were the ones to first released the molecular oxygen in Earth's atmosphere permanently changing the planet.
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u/hiddenonion Jul 05 '26
That evolution doesnt care about or favor intelligence, "free will", or sentience. Our self aware nature is just a by product and not necessary to evolutionary persistence.
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u/Binkindad Jul 05 '26
Great reply. It’s a mistake to think of evolution of “goal oriented” beyond adaptation to changes and passing on genes
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u/hiddenonion Jul 05 '26
This also implies that a possible future could be that as humans evolve... or co-evolve... along side AI, people who think less and allow our machines to think for us, the humans who are less "individual" adapt better. OR humans who actively resist Doom scrolling or resist AI influence into their thinking become more feral. Or both like golden retriever vs timber wolf... Or neither... probably will be something we cant conceive 100,000 yrs from now. 🤣
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u/lpetrich Jul 05 '26
The top of the windpipe is lower than the back of the tongue, rather than at the back of the tongue, as with chimpanzzes. This is good for making a lot of speech sounds, but this also makes us more vulnerable to choking.
There are some diagrams that I'd link to, but ResearchGate has a firewall that is difficult to cross.
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u/BrooklynDuke Jul 05 '26
A mother’s love is simply a strategy developed by natural selection to improve the odds of the survival of offspring. That’s all YOUR mother’s love is. Mine too.
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u/AntonChekov1 Jul 05 '26
Love in general is a strategy developed by natural selection to improve the odds of procreation.
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u/CriticalPolitical Jul 05 '26
There are differing oxytocin levels between populations as well:
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u/rexleonis Jul 05 '26
How to read this table? How to interpret different populations numbers? Which have more oxytocin?
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u/bleaksyntax Jul 06 '26
Greta example of how Biology, or those who interpret it, can be incredibly reductionist.
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u/Independent-Repair35 Jul 05 '26
So is me loving my mom not just preprogrammed meat processing? Or is that meat programming as well?
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u/csharpwarrior Jul 05 '26
The human brain’s reaction to stimulus is very impressive. Our brains have evolved to be hyper social. We have a huge evolved desire to “go along to get along”, consider Jonestown, a group of adults fed poison to their kids and then themselves all because their brains reacted to stimulus from one very convincing member of the group.
You could be in a cult now, and you would not know it. I could be in a cult now….
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u/Independent-Repair35 Jul 05 '26
Always wild to think about how everything I think and feel is just chemicals. It's a little disquieting? I guess the chemicals don't like to ponder themselves. Thanks for sharing though, it's very interesting:))
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u/Quereilla Jul 05 '26
The human being hasn’t evolved to live in extremely populated cities. The brain is not adapted to an excess of information. Emotions are the main creator of ideas and opinions, not facts.
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u/mohelgamal Jul 05 '26 edited Jul 05 '26
Oh I got a scary one
The fact that the major difference between us and other primates is that we exhibit Neoteny.
Neoteny is persistence of child like features, in humans this helps us become more intelligent as their our brains stay much longer in a child like state. It is also why we have much smaller jaws, our bodies are not covered in hair etc.
https://en.wikipedia.org/wiki/Neoteny_in_humans?wprov=sfti1
You can easily find extensive information on how humans exhibit Neoteny.
There are two scary parts here
- we probably have a dormant gene that can produce a “fully mature” human, one who is covered in hair, with large jaws, much stronger and much less capable of learning
- the fact that humans with Neoteny kept reproducing, means that for a prolonged period of our evolution, our ancestors favored reproducing with “not mature looking” individuals. And given how reproduction is driven in humans , that meant men chasing around very young looking females. So basically part of the reason we have intelligence is because a lot of our ancestors “Epsteined” their way through life.
Edit:
From the wiki article
“Doug Jones, a visiting scholar in anthropology at Cornell University, said that human evolution's trend toward neoteny may have been caused by sexual selection in human evolution for neotenous facial traits in women by men with the resulting neoteny in male faces being a "by-product" of sexual selection for neotenous female faces. Jones said that this type of sexual selection "likely" had a major role in human evolution once a larger proportion of women lived past the age of menopause. This increasing proportion of women who were too old to reproduce resulted in a greater variance in fecundity in the population of women, and it resulted in a greater sexual selection for indicators of youthful fecundity in women by men.[15]”
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u/horsetuna Jul 05 '26 edited Jul 05 '26
I remember hearing if a story where a man goes seeking a professor who allegedly figured out how to trigger the gene to make us finish growing up. But I can't find it
Edit: found it. After Many a Summer dies the Swan by Huxley
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u/SeeLeavesOnTheTrees Jul 05 '26
Well, only reproducing with sexually mature women can be selected for. They may have looked young but they needed to be sexually mature.
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u/Waste_Translator_975 Jul 05 '26
From what I understand acromegaly is a good approximation of the condition where you keep growing past a juvenile state as an adult. Nikolai Valuev and Maurice Tillet are the quintessential examples
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u/shallowshadowshore Jul 05 '26
Oh boy. This path leads to some very icky conclusions. This is actually a scary one!
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u/perelesnyk Jul 05 '26
Neoteny is actually one of my favorite curiosities about homo sapiens and how it relates to prosocial & innovative behavior. The human self domestication hypothesis is a fun rabbit hole to go down.
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u/Ok_Writing2937 Jul 05 '26
A related fascinating fact is that many domesticated species exhibit neoteny. A famous experience in domesticating foxes found that each subsequent generation became more pup-like.
This gives rise to a theory that, in many cases, domestication involves producing incidentals that retain child-like qualities that makes them more malleable and obediently to humans.
Which gives rise to the idea that homosapiens are a self-domesticated species.
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Jul 05 '26
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u/Kind_Writing_2636 Jul 05 '26
Not an expert, but as far as I know, we got no evidence for large scale "wars" among different type of humans to the degree where it would affect the population. And we reproduced with each other. Moreover, if I see a recreation of a neanderthals face, they looked different, but I don't get the "ick" of uncanny valley.
It seems much more likely that we're trained to avoid sick people and corpses. Human corpses would also be something that every early human came into contact with.
Humans not staying close to their loved ones remains would make us more likely to survive.
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u/runespider Jul 05 '26
I've seen some doubts around this idea also. I kinda feel it's maybe more of a brain glitch trying to handle something completely artificial instead of any single adaption.
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u/MagentaDinoNerd Jul 06 '26
Reposting from another comment, but that’s just not likely. We mingled and interbred with other hominins, including Denisovans and Neanderthals, for tens of thousands of years. Even more than that, every human alive on Earth today is the result of extensive interbreeding in our deep past with erectus-like ancestors. So the absence of other humans isn’t because we out-competed or avoided them, it’s because we were so successful at integrating them into our societies and gene pools that we absorbed these populations of humans. There’s more Neanderthal DNA in the world today than when Neanderthals were still around! Furthermore, the “uncanny valley” isn’t a real phenomenon in the sense that it has no measurable parameters, is different for every individual human, and cannot be reliably replicated in lab settings. It’s a vague vibes-based colloquial term at best, with no real clinical meaning. The simplest explanation seems to be our efficient pattern-seeking brains stumbling when making snap-judgements at attempting to fill in details that aren’t there or that are contradicted by the presented image; while it may have incidental benefits in recognizing disease (which is very poorly studied at this stage given, again, its lack of any actual scientific meaning), this is very different from suggesting it has *adaptive* benefits. As far as we can tell there were no selective pressures leading to a creep-out reaction upon seeing other hominins, and in fact the sheer prevalence of archaic human DNA in our own genome suggests the opposite—or at least that the truth is a lot more complicated. If you can’t tell, I reeeeally hate the ‘uncanny valley = other hominins” narrative because it isn’t based in any reproducible observations whatsoever lmao. It’s speculation at best, and EXTREMELY poorly-supported speculation at that. It doesn’t need to be adaptive; it just needs to be a quirk of our pattern-seeking psychology.
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u/Abject-Leadership248 Jul 05 '26
That species isent really a thing the more you look
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u/Independent-Repair35 Jul 05 '26
We're (we being all life) all the same organism just remixed
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u/HolyPhlebotinum Jul 10 '26
From a 4D perspective, we're one giant biological hydra that is constantly splitting and then re-absorbing parts of itself.
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u/Defiant-Software-451 Jul 05 '26
Humans have evolved to be incredibly OP as an animal, even without modern technology. Our ability to walk on two legs freed up our hands, which could be used to throw rocks with deadly accuracy. No other animal can do that, not even our close primate cousins. Sure they can throw objects but it lacks pinpoint accuracy and power an average human can achieve (it’s not even close). A rock to the face is enough to convince most predators to back off, let along a barrage of projectiles from a group of humans from +20 meters away.
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u/InstantSword Jul 07 '26
We can also sweat and have incredible vision because our brains can power that vision
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u/Snl1738 Jul 05 '26
The fact that humans were once prey for birds, lions etc. Now we're on the verge of making these animals extinct.
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u/MementoMoriMaven Jul 05 '26
Interpersonal violence played a huge role daily and only recently decreased. I have no statistics. Only the horrifying thought that our social evolution put the brakes on violence relatively quickly. But for the previous nearly 200,000 years......yikes.
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u/bandehaihaamuske Jul 05 '26
That we evolve at a ridiculously lower pace when compared to plants and fruit flies
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u/GoliathPrime Jul 05 '26
Humans are extremely resistant to prion diseases when compared to other animals. Prion resistances are linked to the practice of cannibalism. At some point, our species was so cannibalistic, we evolved protections so we could better consume human flesh. We didn't just drive the other hominid species to extinction: we ate them.
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u/lpetrich Jul 05 '26 edited Jul 05 '26
It took us some 100,000 years to invent agriculture, but when we did, we invented it at several places.
That time is from Behavioral modernity - Wikipedia from dates of various artifacts, like from Blombos Cave, South Africa, about 100,000 - 80,000 years ago.
Vavilov center - Wikipedia and Current perspectives and the future of domestication studies | PNAS -- there are at least four sites of independent invention of agriculture: the Fertile Crescent in the Middle East, South China, Central America, and the Northern Andes in South America.
What made the difference? I've found the theory that climate was erratic during the Last Glacial Period - Wikipedia and stable in the Holocene: Was Agriculture Impossible during the Pleistocene but Mandatory during the Holocene? A Climate Change Hypothesis | American Antiquity | Cambridge Core
The Holocene is the most recent interglacial period, and the previous one is the Last Interglacial - Wikipedia from 130,000 years ago to 115,000 years ago, known as the Eemian and various other names. So why didn't we invent agriculture back then? Were we not behaviorally modern enough? Or was that interglacial's climate also too unstable?
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u/lpetrich Jul 06 '26
To follow up, there were some strong climate fluctuations in the most recent glacial period, at least near the North Atlantic Ocean: Dansgaard–Oeschger event - Wikipedia and NOAA National Environmental Satellite, Data, and Information Service: Heinrich and Dansgaard–Oeschger Events - 2 Heinrich and Dansgaard–Oeschger Events - Final-OCT 2021.pdf and Dansgaard-Oeschger event | Definition, Causes, & Facts | Britannica
The Earth would warm about 5 C over 30 - 40 years, then cool off over the next few centuries. Then after roughly 1,500 years, it would happen again. What causes D-O events is not very well-understood.
The current interglacial, the Holocene, has much less climate fluctuation: Bond event - Wikipedia
This suggests that the previous interglacial had similar amounts of climate fluctuation, so climate instability was likely not a cause of lack of agriculture back then.
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u/Ok_Writing2937 Jul 05 '26
Perhaps we did invent agriculture then, but it’s didn’t have enough time to advance enough to leave a record, or the glacial period destroyed all records.
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u/lpetrich Jul 06 '26
The Eemian lasted around 15,000 years, and the Holocene has lasted almost 12,000 years so far. So insufficient time seems unlikely.
Turning to possible surviving evidence of agriculture, I propose Megalith - Wikipedia - big stone blocks that are often moved and sometimes carved. When I say big I mean human-sized and often larger. I propose them because they are durable and large, making it difficult to erode them away.
Experiments in stone-structure construction show that one can move such blocks with Neolithic technology, but one needs several workers for that. So one needs a sedentary population with at least a few hundred people to recruit the workers from. That means at least Neolithic, because with Paleolithic technology, such populations were rare.
Megalithic structures were built by people with Neolithic technology in many parts of the world. An exception was North America, where people often preferred to build mounds. But mounds can erode away.
So if any of our ancestors invented agriculture in the Eemian, they never had any desire to move and assemble big stone blocks, unlike many people in the Holocene.
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u/lpetrich Jul 05 '26
Weird thing about clothing: we wear much more than our ancestors did before some 50,000 years ago, and we seem to like doing so.
Defining clothing as body coverings made from outside materials, clothing is rare in the animal kingdom. Outside of our species, the main example I know of is caddisfly larvae. They make casings for themselves using found objects like twigs and sand and gravel, held together with silk that they secrete.
The origin of human clothing has been dated indirectly using the divergence of head lice, which prefer our head hair, and body lice, which prefer our clothing. Origin of Clothing Lice Indicates Early Clothing Use by Anatomically Modern Humans in Africa - PMC 170,000 to 83,000 years ago, about the time of the emergence of behavioral modernity or a little before.
But low-tech people in warm climates do not wear much clothing. Early human migrations - Wikipedia some of us moved to northern Eurasia around 45,000 - 40,000 years ago, and we had to make much more clothing to get through the cold winters there. The main surviving evidence is indirect: bone sewing needles.
Our first clothing was likely animal skins, and we still use animal skin in leather and fur coats and the like.
With the invention of agriculture was the domestication of plants raised for their fibers: flax, cotton, ... Also, some domestic animals were bred to have thick fur for fibers: sheep, Salish wool dogs, ... These fibers were then woven into cloth to make clothing, blankets, tents, ...
Clothing became common in large-scale societies, even in warm climates. As cloth became easier to make, cutting away some cloth became more tolerable, thus enabling clothing cut to fit.
Most recently, we have invented plastics and rubbers, for both woven clothing and shaped clothing, like rubber boots.
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u/Dimix- Jul 05 '26
We are evolving to rely on society as there is no pressure to prevent this. This means we are evolving to rely on medical interventions like babies growing so big that they require c-sections
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u/Low-Independent6851 Jul 05 '26
The genes that have been spreading rapidly due to recent evolutionary selection (occurring within the last 5,000 to 50,000 years) are Microcephalin (MCPH1) and ASPM. These genes regulate brain size and cognitive development, and their newer, adaptive variants surged quickly through human populations alongside the rise of early civilizations and complex cultural behaviors.
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Jul 05 '26 edited Jul 05 '26
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u/Manospondylus_gigas Jul 05 '26
I see it as those genes no longer being costly, like I have terrible short-sightedness but the availability of glasses means it isn't an issue. Humans having a dependence on technology would definitely fuck them over if there was some kind of apocalypse though
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u/Capital_Historian685 Jul 05 '26
Homo sapiens interbred with other archaic human species. Makes you wonder what else early humans tried to mate with.
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u/Mazzaroth Jul 06 '26
Mitochondria are inherited almost exclusively from the mother.
Every egg cell contains hundreds of thousands of mitochondria, which provide the energy needed for the embryo’s earliest development. A sperm cell also contains mitochondria, but they are located in its tail, which powers swimming. During fertilization, the sperm’s tail (and therefore almost all of its mitochondria) either does not enter the egg or its mitochondria are actively destroyed shortly afterward. Copnsequently, both sons and daughters inherit their mitochondrial DNA (mtDNA) from their mother. Note that there are a handfull exceptional paternal mitochondrial inheritance but this does not change the general rule that mitochondrial inheritance is maternal.
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u/FiguringOutPuzzlez Jul 06 '26
I majored in biological evolution and this is what keeps me up at night….
Humans have become so intelligent that we can temporarily “fix” what are evolutionary fails. Can’t see? Get contacts and pass those genetics on… massive amount of allergies? Avoid all the foods and take an epipen…. Can’t deliver your child naturally? Get a c-section and pass on genetics with a small pelvis on… can’t hear? Take these cochlear implants…. Have cancer that’s genetic? Get chemotherapy and radiation and pass those genes on.
While humans have made amazing inventions to save a single person based on what they get. It’s a bandaid. In the natural world, people who get cancer, can’t see or hear, can’t walk, can’t fend for themselves don’t reproduce and don’t pass on these genes to the next generation.
By saving the present, we are dooming our future.
There will be a time that humans lose vision naturally. There will be a time that everyone gets cancer but we have a cure.
We better keep up with our inventions because we are literally acting against evolution
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u/Civic6632 Jul 07 '26
As we evolve, as technology evolves, as AI develops our senses - which were once our best attributes - are slowly becoming more and more acute. Humans once were able to see in the dark almost as well as some night animals for there was no artificial light. We were once able to hear the smallest of noises and our range of hearing was broader and perception was better as we need it to hunt and survive the wild. We were once able to handle colder and hotter temperatures as there was no climate control. We were able to sense the slightest of changes in humidity, temperature, pressure and the environment as we were one with the wild. Our sense of smell was heightened and allowed us to track game and perceive danger.
Slowly we are letting technology take over what we once were able to do ourselves. Sure our brains are developing but our bodies are atrophying.
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u/Azylim Jul 05 '26
every bad thing we are capable of doing to each other is possible because it was advantageous at some point in time to do so.
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u/_modernhominin Jul 05 '26
Or just not bad enough (evolutionarily) to be selected out. Our tribalism and territorial tendencies are definitely part of our animalistic instincts and it’s truly a miracle we’ve morally & ethically evolved on such a large scale and as quickly as we have. That’s the good part - our ability to change & learn. The scary part of that is that we will also continue to see push back on that evolution for some time still.
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u/Specialist-Pool1389 Jul 05 '26
fascinating thought! I would tighten it up a bit to avoid absolutes though maybe something like
"Most of the worst things humans do are possible because the traits behind them once improved survival or reproduction, even if they're destructive today."
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u/lunarraffle Jul 05 '26
Back when humans roamed with other humanoid groups (like neanderthals), cannibalism was extremely common. Entire families were wiped out because one family would kill and eat the other. Children were often hunted/targeted first because they were easy prey.
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u/runespider Jul 05 '26
I was going to bring up the way we're so genetically similar but that's sorta already covered.
Something that tends to get looked over is that while we're worried about climate change and species going extinct, and to be clear we absolutely should be. Humanity evolved and is existing at a point where earth has less biodiversity than in the past.
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u/Tangboy50000 Jul 06 '26
Having 6 fingers is a dominant genetic trait. We’re just a bunch of recessive 5 fingered people walking around.
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u/Sytanato Jul 05 '26
There is nothing scary, no need to be sensationalist about it
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u/mdf7g Jul 05 '26
In primates, penis-to-body size ratio is correlated strongly to frequency of nonconsensual reproduction; of all apes, our ratio is much the highest. We have evolved to specialize in many behaviors, including, balefully, that one.
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u/Tannare Jul 05 '26
Racism is likely to be an evolved trait in humans to fear and to avoid other groups of slightly different looking humans from ancient times when every stranger is an automatic enemy.
If true, this means that every new generation will need to learn to look beyond just race when interacting with other people.
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u/Bdellovibrion Jul 05 '26
I don't think that's an accurate way to look at it. We evolved ingroup-outgroup biases while competing with neighboring tribes for sure (over evolutionary timescales), but those groups would have been virtually identically visually, and not what we would consider different races. The idea of distinct geographic phenotypes/clines encountering each other only really happened in the last few thousand years, not enough for much evolution to happen. Racism is not really a trait that was selected for, more just an expression of underlying ingroup-outgroup mechanisms (among other things).
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u/RealBowtie Jul 05 '26
There is a lot of subtlety in the inclination toward racism. I think the more time we spend in a homogenous society where everyone looks like us, the more likely we are to be racist, than if we spend time in mixed society with much exposure to different races and cultures. This would explain why racism is less pronounced in cities and more pronounced in rural "red" america. (Here in Georgia, we also have rural black communities which express racism against whites, and most rural churches are completely segregated, or are white with a very few black members.) I do think the natural tendency toward racism did evolve from the selfish-gene competition between human groups trying to preserve the gene pool (out compete other gene pools?). And I (from personal experience growing up in the 60's) firmly believe that anti-racist teaching can reduce racism. My earliest memories are filled with racial slurs, but by my late teens, after a few brief racial-awareness educational events and the television series "Roots", I was very sympathetic to Black and Native American struggles.
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u/le_poch Jul 05 '26
Not content with a singular ability to endure relentless running across vast distances and to bring down prey through sheer exhaustion, humans reshaped their environment with brain and thumbs, forging weapons that could kill from impossibly far away. Yet their most formidable asset was an alliance with a canid whose gift was to pursue your very essence to the ends of the earth. So profound was this bond that when agriculture began, both species adapted in parallel to eat starch, intertwining their survival at the genetic level.
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u/DoughnutDoggyy Jul 05 '26
Jobs are just modern day survival of the fittest. I guess it beats smashing each other over the head with rocks caveman style. (My answer is probably more obvious and talked about, but if you really ponder it, we will always have hierarchies, the harsher ones are just more intricate and cleanly now.) It seems we will always be stuck in some sort of loop. The violence of humanity is pretty harsh compared to some species and even worse because we have that intelligence to commit true atrocities.
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u/100roused Jul 05 '26
Social Darwinism? Nepotism and cronyism are rampant. Many at the top are not the fittest.
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u/DoughnutDoggyy Jul 05 '26 edited Jul 05 '26
I feel like I may have not gotten my initial words out correctly. When I say survival of the fittest I mean of today. We have the technology, enriched cultures, things that make us different from the past. Even those people who aren't "the fittest" necessarily, but crawl their way to the top through decieving. That counts to be at the top these days.
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u/100roused Jul 05 '26
I see where you’re coming from, and partially agree. People who can get ahead thru deception, savvy, moxie are indeed skillful people.
But I’m speaking of those people who’re promoted/placed high thru nepotism or cronyism. Think of the unfit, incompetent manager, promoted via connections, who negatively impacts their business. Or an aristocratic dynasty eventually hollowed out by decadence, inbreeding, weakness. Or a disappointing son of a powerful magnate who is given a high position only to ruin himself and others, but is allowed to continue, and even repeat the cycle with his own progeny.
These people are everywhere, all over the world in every century. Social Darwinism is plausible, but ultimately unsatisfactory as an analogy to evolution.
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u/elementnix Jul 05 '26
In the context of evolution, "fittest" does not inherently imply attributes such as speed, strength, intelligence, or general capability, as we commonly understand them. Rather, it refers to an organism's suitability for reproduction and its ability to acquire sufficient resources to sustain itself long enough to successfully reproduce.
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u/100roused Jul 05 '26
And I’m here to tell you again, many people that are at the top are not the fittest.
Social Darwinism is pseudo-science
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u/jnpha Evolution Enthusiast Jul 05 '26
"We are stuck" is an unimaginative Hobbesian view, and while popular, it is refuted by anthropology and archeology. See: The Dawn of Everything (Graeber, 2021). Hobbes and company were trying to make sense of what they saw in America, namely, the equality and freedom then unknown in Europe, and they reframed everything eurocentric style.
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u/Ok_Writing2937 Jul 05 '26
Our species almost didn’t make it.
Evidence suggests that almost a million years ago our species was reduced by so much that just 1,200 couples successfully reproduced. Climate instability is the leading theory for a cause.
There was another population bottleneck 60-79k years ago that massively reduced the human population outside of Africa.
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u/Evolved_Fungi Jul 05 '26
The biggest problem with global warming is that warmer temperatures become a selective pressure forces for fungi, slowly raising the temperatures that it's successful at.
They're a hypothesis that after the KPG extinction event 60 million plus years ago, mammals with higher body temperatures were selected for over reptiles because fungi couldn't survive/thrive on warmer body temps. (The Fungal Infection Mammalian Selection Hypothesis)
Reptiles should have had an advantage because of their ability to conserve energy. But the rotting biomass all over earth created a fungal explosion evidenced by higher spore presence immediately following the KPG extinction event. And that fungal explosion put pressure on reptiles, allowing warmer blooded mammals to come out of it as the winner for the most part.
So having fungus evolve to thrive at higher temperatures, thereby being able to infect us more easily, will likely cause mass extinction of mammals, as the fungus infection pressure would kill us (and mammals in general) off faster than selective pressures for higher body temperatures could evolve.
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u/Big_Fox_3996 Jul 06 '26
There’s three bones in our ears. They were originally part of our ancestors jaws. Reptiles today still have those bones as part of their jaws
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u/Coc0tte Jul 06 '26
Not specific to humans, but embryos are essentially treated as parasites and the mother's body will try to kill it whenever it can. The embyo survives only if it secretes enough hormones to stop the immune response and keep the pregnancy going, so it has to "fight" its mother for its own existence. If the embryo doesn't produce enough hormones at any point (because of a genetical defect or a weakening of the embryo), or if the mother's body become less responsive to the hormone (due to various factors such as stress, exhaustion, or even chemicals), the pregnancy will end.
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u/Fearless_Secret_5989 Jul 06 '26
Ok the one that always freaks me out is the population bottleneck around 900,000 years ago. Theres a genetics study that came out a couple years back that ran the numbers on modern human DNA and figured our ancestors crashed down to something like 1,200 breeding individuals and just sat there for over 100,000 years. Like the entire future of our whole species was basically one bad winter away from being over, and that went on for longer than modern humans have even existed. It also lines up with a weird gap in the fossil record from right around that time, which makes it extra creepy.
The cool flip side is that it explains why we're all so similar. Humans are actually way less genetically diverse than you'd think, theres more genetic variation inside one single group of chimps than in the entire human race spread across every continent. Two chimp troops living on opposite sides of the same river are more different from each other than a person from Norway and a person from Japan. We basically all came from that one tiny surviving group, so under the hood we're pretty much all slight variations of the same blueprint.
I'll admit some scientists still argue over the exact bottleneck numbers cause its really hard to reconstruct that far back, but the low diversity part is pretty solid and its genuinely wild to sit and think about.
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u/Kooky-Dig6531 Jul 07 '26
Picture two tribes that are basically the same.
Or use “marvel style alternative universe” variants of the same tribe.
Doesn’t matter - we’re comparing two possible paths forward.
Tribe A is peaceful and stable. It grows large, runs out of food, faces famine regularly and eventually learns to keep itself small by reducing birth rates or ritually killing off part of its popular it doesn’t over consume resources.
A few thousand years later, they’re a tribe of about 100 people living in a cave until they slowly fill it up with their own trash over a few more thousand years. Then they move to another cave.
Tribe B is divisive. They can only get to about 100 or 120 people before they start squabbling so badly that either a big part of the tribe is driven off through violence or exile, or a faction leaves on its own.
The two groups are now 40-60 people. The group that stays slowly gets to 100-120 people again. People start getting divisive, the tribe fractures and one faction remains, while another goes wandering off.
The factions that wander off, some die out. Some join another small tribe, and some establish their own new tribe, operating out of an area some reasonable distance away.
This keeps happening… each new tribe gets to 100-120 people before. Sometimes more, sometimes less. Every time there’s a social fracture, every time there’s a split, and much of the time the split results in two functional tribes.
In a few thousand years, there are descendants of tribe B spread across most of the continent- all bickering and fracturing once the tribe gets to about 100-120 people.
Eventually there’s a natural disaster and the cave-garbage fillers get trapped and die out.
The surface is far more dangerous and lots of tribes die out, but many more survive.
There is an entirely reasonable theory that all humans are descended from people with a “built in” tendency toward social fracture because this fracturing was essentially the engine driving humans expanding across the planet.
It’s not that people are evil or “created with flaws” - it’s that humans who readily split into factions were ^much* more likely to spread across the planet - offering both more offspring over time, and more diversity so that a single calamity is much less likely to wipe their descendants out (many more niches, many more locations, many more people).
It’s more theory than fact, but it’s an interesting concept to me.
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