I live in a world where 90% of my friends and family believe that they came from the sins of a woman who decided to eat an apple. I recently read a book called Sapiens, this book really drilled into my mind that we homo-sapiens are a derivative of a single great ape that had two daughters, one that became the ancestor of all chimpanzees and the other all humans.
If human origin interests you there is a great 10 minute video from the Youtube Kurzgesagt channel that lead me to read Sapiens.
Minor derailing: it's not necessarily accurate or useful to think about speciation as "one parent with two divergent children". It's usually more about populations with fuzzy boundaries.
Speciation events tend to look more like, imagine you take a town of two thousand people and send half of them to the moon for a million years. The moon men and the earth men would evolve into two different species; if you looked really hard, you could find a single common ancestor from whom everyone in that town descended, but it's not like one of his children went to the moon and one stayed on earth; some of his great-great-*-grandchildren went to the moon and some stayed on earth. The common ancestor was hundreds or thousands of years before the population split in two.
Moreover, breaks don't always happen cleanly. Imagine for the first ten or hundred thousand years someone from earth would occasionally migrate to the moon or a moon man would return to earth. The same thing would have happened with proto-humans and proto-chimpanzees: long after the two species had begun to diverge they would still be interfertile, and some mating (or "gene transfer", if you prefer) would still happen long past the point you'd begin calling them two different species. Eventually the two species would stop being mutually fertile or even attractive and the rift would be complete, but look at how many big cat and horse-like species can still occasionally pull it off.
Evolution is messy, and the bush of life is complicated.
As an extension of that fact, if there was a single true Eve the population would be at extremely high risk for genetic defects.
It's called a population bottleneck, where a near extinction event forces almost all individuals to share a large proportion of their genetic material, and the most recognizable example is in cheetahs.
It only applies to mitochondria, not the genes in the nucleus or anything constructed from those genes.
It's only unique because the "MR" in MRCA stands for "most recent".
You could have a species that's a million years old with an MRCA that's only 500 years old. You could also have a species with no MRCA. (As in, the only way to find an MRCA is to trace back into ancestor species.) Picture two islands where only males travel between them.
Mitochondrial Eve is the most recent common ancestor of our mitochondria. But that only tracks purely mother-to-mother descent; there could be a more recent female common ancestor.
Consider the hypothetical population consisting of two people, whose fathers were both first cousins and whose mothers are second cousins, on their mother's... side.
Their mitochondrial MRCA is their great-great-grandmother on their mother's side, but their MRCA's are their great-grandmother (and great-grandfather) on their father's side.
The entire human family tree is like that, but way, way more complicated.
My dad was a geneticist at Harvard and we lived across the street from Stephen J. Gould. When people on Facebook are having a conversation about how Benghazi is a sign of the second coming of Christ, I sometimes take a moment and question my own beliefs. The foundation of my beliefs isn't because someone said punctuated equilibrium is a thing but that tests can replicated and peer review scientific research can stand the test of time.
I don't think peer review is one of the foundational ingredients. Scientific work should be repeatable and falsifiable, IMO that is all that really matters. These two properties are already hard to muster though.
Peer review as currently done certainly isn't foundational to the scientific method, but the general principle of having ideas checked and examined by as many other minds as are capable of understanding them, does lead to stronger and more reliable ideas over time. Not everything that science deals with is quantifiable or directly testable; results must be interpreted, and theories have to be made about the wider reasons for those results in order to come up with the next set of experiments; this is the realm of discussion and argument, rather than measurement or direct tests, and science is best advanced when there is strong, productive discussion among competent arguers.
In centuries past, with small experiments, "peer review" actually was replication—your peers would go and do the experiment themselves and confirm your finding.
Insofar as experiments are now too large and costly to allow for "I'll just go check that in my lab tonight"-type replication, peer review is increasingly just a status game.
The most valuable thing about peer-reviewed journals isn't that a handful of chumps proof-read the articles before publication but that the journals are widely circulated and read by the appropriate set of scientists and technicians. One of two things will happen after publication.
The paper will have no impact, no one will base any further work on it, no one will cite it, and it will vanish like a fart in the wind. In this case, the author gets minimal prestige, and can claim a publication in a maybe-prestigious journal with an embarrassingly small number of follow-up citations. No fame, money, or power for the author, and no impact (negative or positive, if the paper was right or wrong) on the world.
Or the paper can spark a lot of ideas in the people who read it. They'll try to build on it, or they'll try to use a technique from it in another application. When this happens, if the paper was solid, then the original author gets citations, speaking engagements, money and power. If the paper was less than solid, and the people trying to build on it keep having trouble, that is when the original author's house of cards comes crashing down.
You don't need to directly replicate an experiment when you can build on it. If your experiments building on the original experiment make sense and give consistent results, you've just validated the original research in another way. If your experiments don't, and after weeks and months of wasting time checking your own work and making sure you're not doing wrong, you slowly reach the conclusion that the original research was bogus, then you begin to get angry. Then you begin to tear into the original author and his research, publicly denounce him for wasting your and everyone else's time. Then science self-corrects.
So science is generally OK -- either bogus research that gets published has no impact (no different that a lot of good research :-P ), or it proves false when other people try to build on it.
Who gets into trouble, is science journalists and laypeople who read newly published articles and assume they are gospel.
You're talking about the kind of sciences with applied-science subfields, where experiments form a natural hierarchy with new knowledge necessarily building upon old.
Fields like psychology, on the other hand, need replications—"assuming another result as axiomatic in your own experiment" just doesn't come up much.
Why do you think researchers in the various subfields of psychology do not build on each others' work? What do you think they are doing when they read each others' papers and cite them?
I as told in Jr. High School that we ended bipedal in order to stand in the bush so we could see further what was coming up and then, with our hands now free, we could start building tools and use them. I don't know what this explanation is worth but I find it makes a lot of sense.
I am sure you are being downvoted for mentioning Betteridge. I upvoted you because using causation to describe evolution is inherently flawed. Discussing it in that framework only confuses the nature of evolution. Our ancestors didn't become bipedal "because" of any one thing in particular. None of our ancestors were sitting around saying "Hm. I wonder how we can influence our future evolution." "Well, it would be nice if we could throw." There were likely a lot of benefits to bipedal motion in early humans and that's why they out survived those on all fours.
Perhaps the fault is with the English language itself that the article and this post's title both imply that humans became bipedal in order to throw. I use the word 'fault' because of course that is not how evolution works.
While the origins and order from millions of years ago may remain unclear what is clear is that by the time individuals had achieved the pathetic defensive and offensive weapons of the modern human body something else had to be going on.
A single modern human on the plans of Africa would almost instantly succumb to the carnivorous interests of any number of hungry beasts. Modern humans in their modern bodies alone have just nothing to inspire fear in anything bigger than a koala bear.
One aspect is clear, humans living in groups are more viable, but that gets you only so far. A whole group of humans facing the local lion with just their bodies alone would just be chomped down one by one.
While throwing is not bad for hunting it's particularly devastating when combined with stones and a group of humans for defence. Humans with a bit of practise are stunningly accurate with throwing stones at speed. Imagine a group of lions (or any other predator really) facing 20 or more humans throwing stones with deadly intent. Humans in this circumstance are instantly transformed from the neighbour weakling to a defensive force of undeniable leathality and terror.
The real beauty of it is that the human doesn't have to be near the target to impart the stinging blow. Other natural weapons red in tooth and claw require the aggressor to make contact with the prey and possibly suffer injury. Thrownn rocks avoid this danger entirely.
Hunting requires many different strategies of which stone throwing may be one. Defence in the dark of night from a closing dread predator would be best effected with a hail of well placed stones every few seconds. Very few predators would be willing to risk it for very long.
Luckily for humans, herds of elephants only eat vegetation.
Generally living organisms become bipedal when they have another use for their legs other than walking. See birds. In our case it was the usage of tools.
My interpretation is that the second pair of legs (arms) only gets in the way, if you want high speed on a plain. That is true for both theropods and primates, just look at a chimpanzee running...
Horses and cheetahs both seem to do fine, and much better than humans.
Also, the human body-plan seems set up such that a running human has dynamic instability: we run "better" by pumping our arms around, keeping balance with the shifting mass rather than purely relying on our legs to do that job.
Horses (and various ruminants) are a bad example because they need a relatively big mass of fiber in their digestive tracts. Can't do that on two legs. Still, their fore legs are considerably lighter and contribute relatively little to forward motion.
For that matter, a human can run down a horse. Some Africans still do that with zebras. Cats can't do that.
And no, "pumping" arms around is not really a necessity.
Again, Humans have done this as a hunting strategy for at least as long as there is H. sapiens sapiens. Pick an individual animal, run after it until it collapses.
I guess the horses they hunted weren't as well trained, bred and fed as those in sports competitions. Wild horses in general evolved to run occasionally over relatively short distances.
Yeah, I wasn't posting it as contrary evidence. Note the part where humans do win.
Several humans working together in familiar territory would likely be able to start an animal sprinting several times in fairly rapid succession and avoid the marathon.
They run better over short distances. Bipedal great apes do better over long distances. This is proven both by experienced hunters and myself as I hunt down my cat for kisses. After just a few minutes, she hunker down and accepts her fate since I can literally jog around my house all day.
Is there an evolutionary story for why T. Rex ended up bipedal with mostly-vestigial forelimbs? It works fine for their ecological niche, but I can't picture the evolutionary intermediates between them and a quadrupedal ancestor.
Actually, there's a very simple reason: the T. Rex had stubby arms so it could have a big head.
The T. Rex started out bipedal, with functional arms -- you can pick that as its starting point, there are plenty of those guys running around in the fossil record. As its head got bigger and bigger, it became top-heavy: its back end had to balance its front end when running, or else it would just face plant constantly.
If I had to guess (I haven't actually looked into how much of this we have recovered from the fossil record; I just happen to have heard the reason above) the T. Rex's head probably got pretty big first -- for a while, bigger heads could be counterbalanced by bigger tails while still retaining normal-sized arms. But there's a limit to how big animals can get, so eventually the proto-T. Rex would have the biggest tail it could support.
By this point it would be firmly in the big head niche: its diet, survival strategy, and sexual selection would revolve around using its giant head and powerful mouth to just bite the crap out of everything and generally be awesome. Now come the tiny arms: even when its arms were still functional, they were less awesome than its giant head. Trading slightly smaller, slightly less functional arms for a slightly gianter, slightly more awesome head was a win at every point down the curve, until it was stuck with tiny, useless arms and a really awesome head.
The current thinking is that T. rex used its stubby arms to grasp prey when it went in for the kill. A similar line of thinking applies to the flapping wings of birds: earlier theropods flapped their forelimbs in order to help hoist themselves on top of their prey to make the killing bite.
Their common ancestors may have evolved bipedalism because forelimbs proved cumbersome when taking down large prey.
We're dealing with larger than mountain lion scale beasties here. Fun fact about hippos: they can't jump. Like at all, unless they're submerged and can use the buoyancy of the water. The same is true of just about any modern tetrapod within that size range. If you're a tetrapod the size of a mountain lion or even a bengal tiger, you can still have speed, agility, and the ability to spring, pounce, and grapple with the forepaws. At T. rex scales, the square-cube law has something to say about that.
Given that humans are otherwise well adapted as pursuit hunters, able to select a single prey animal and run it to heat exhaustion - it makes sense that bipedalism is another adaption for endurance running.
Throwing, specifically? I would have thought the advantage being selected was the ability to use two limbs for fine motor tasks: building, throwing, grasping, pulling, knapping, etc...
Ah, but other apes can already do many of those things (and some of them better, given that they basically have four "hands" instead of two hands and two feet.)
The question is what forced humans into this particular, odd body-shape that no other ape has. Long-distance running (for "endurance" hunting, where you just tire out the thing you're chasing) has been the hypothesis I've heard the longest, but running and throwing works too.
Fair point, but I was considering the fact that being bipedal allows you to constantly be doing one of those things. Simply being able to carry things around over long distances seems like a bigger advantage than throwing.
Of course this is all speculative, and I suspect that the point of the Nautilus article was to entertain the thought, so in that respect it's a great article.
>Long-distance running (for "endurance" hunting, where you just tire out the thing you're chasing)
I've recently read claims (though I forget where -- primary sources, if memory serves) that directly contradict this point (which I'd also heard). From memory:
- foot structure is ill-adapted to continuous running (stress fractures, I believe)
- knees are also problematic
- some physiology / metabolitic arguments
I must also admit that this hypothesis seems fishy if only because I can't think of many tasty animals that man can actually keep up with...
> I can't think of many tasty animals that man can actually keep up with
"Long-distance" doesn't have to imply "in a straight line", keep in mind. If we can herd prey in arbitrary directions, we can have other members of our tribe stationed where we're herding them, turning the marathon into either a pincer trap or a relay race.
Cool, would love to read through that. I feel like I got a solid understanding of this sort of topic based on the position that was popular a decade or so ago, and then haven't really kept up with the debate since then.
> I imagine it would be quite awkward running on all fours while holding on to your spear.
"On all fours" isn't quite what our common primate ancestors do on the ground, though. Picture a gorilla: the "hands" are knuckled. I imagine it'd work alright to hold a small tool (e.g. a stone dagger) in them, though not anything as long as a spear.
seems quite plausible, also in the light of (disclaimer: this is not coming from an anthropologist) a notion that the performance of 300 000 year old spares were to rival that of today's high-performance carbon spears (translated in meaning). The latter appears to be quite irritating and would fit the argument of the bipedal suggestion from the linked Nautilus article.
The 300k years coming from the newspaper article below:
Conard et al., Excavations at Schöningen and paradigm shifts in human evolution and
Schoch et al., New insights on the wooden weapons from the Paleolithic site of Schoeningen
William H Calvin makes a similar argument in _The Throwing Madonna_ (and less succinctly, but more entertainingly, in _The River That Flows Uphill_). He's got a lot to say about the evolution of hand-eye coordination and throwing as well.
If human origin interests you there is a great 10 minute video from the Youtube Kurzgesagt channel that lead me to read Sapiens.
https://www.youtube.com/watch?v=dGiQaabX3_o
https://www.amazon.com/Sapiens-Humankind-Yuval-Noah-Harari/d...