Did Our Ancestors Become Bipedal So They Could Throw?
nautil.us
nautil.us
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...
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.
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.
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.
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 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.
Fields like psychology, on the other hand, need replications—"assuming another result as axiomatic in your own experiment" just doesn't come up much.
The same across-the-chest muscle setup that makes us good at throwing also allows us to throw an effective punch.
"push against the ground with your feet to exert significant force using your hand" must have many, many uses.
From both the editorial title law, as well as the flawed logic of causation to draw a conclusion on evolution?
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.
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.
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.
https://en.wikipedia.org/wiki/Man_versus_Horse_Marathon
Humans win occasionally.
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.
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.
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.
Their common ancestors may have evolved bipedalism because forelimbs proved cumbersome when taking down large prey.
https://en.m.wikipedia.org/wiki/Endurance_running_hypothesis
http://www.meltingasphalt.com/music-in-human-evolution/
And the research into the evolution of shoulders doesn't really contradict this.
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.
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...
"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.
I'll try to dig up the refs tonight, because it makes for interesting reading.
Of course, bipedal might have evolved before spear carrying, rather than being driven by it.
"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.
The 300k years coming from the newspaper article below:
Filser, Hubert, 300 000 Jahre alte Speere können mit modernem Olympia-Gerät mithalten (newspaper article) http://www.sueddeutsche.de/wissen/archaeologie-jahre-alte-sp...
which in turn seems to refer to:
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