Recent comments in /f/askscience

jacqueline_daytona t1_j9i8oam wrote

Reply to What are more accepted hypotheses that similarly explain the aspects of hominid evolution that the "pseudoscientific" aquatic ape theory does? by KEVLAR60442

Biological anthropologist here. To add on to what others have said, another idea is that we're meant to be energetically efficient. We know from lab experiments that bipeds burn about half the calories that same sized quadrupeds do when walking. Standing up meant that we individually need less food to survive and could support larger populations on the same land than a quadruped could.

There's also the Provisioning Hypothesis, which relies on the idea that our ancestors were monogamous and that bipedalism freed up the hands in order to gather food more efficiently. Prehistoric monogamy seems like a big jump, but when you compare us to the other primates, the male/female size differences are pretty mild. They're more like what you see in monogamous primates like gibbons and less like ones that have "harem" social structures like gorillas, where the males are much, much larger than the females. (Honestly, I still think it's a bit of a leap though.) Monogamy meant that males can be reasonably sure that their mate's offspring are also theirs, so it makes sense for the males to help supply the females and children with food from a reproductive success viewpoint. The extra help feeding the offspring would free the females up for having pregnancies that were a little closer together, and even a slight increase in reproductive rates can lead to outcompeting other groups without that adaptation.

My biggest complaint about the AAH is that the archaeological evidence says that humans seemed to take a very long time to figure out that seafood was delicious. We don't have ample evidence of humans or hominins exploiting aquatic resources until the past 100,000 years or so, at which point we were anatomically the same as we are today.

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Marsdreamer t1_j9i7yo9 wrote

Reply to comment by Somnif in What are more accepted hypotheses that similarly explain the aspects of hominid evolution that the "pseudoscientific" aquatic ape theory does? by KEVLAR60442

Pretty true. To kinda expound on that, it works "up," but it can get stuck on local maxima rather than global maxima. Picture two mountains separated by a valley and one being higher than the other. If a species is 'climbing' the smaller peak of fitness then once it gets there it can theoretically never climb down the valley and start climbing the taller mountain. It will always* be stuck on that smaller peak because Evolution doesn't know how to take short term pain for long term gain. It's effectively a greedy algorithm to borrow from a CS concept.

*As long as conditions stay exactly the same. The adaptive landscape is always changing.

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dcs1289 t1_j9i74cj wrote

Reply to comment by Krail in when a limb gets amputated, how do they stop the flow of blood? by EnchantedCatto

Capillaries are everywhere. It's the end point of the circulatory system everywhere, so there are beds of capillaries in basically any living tissue.

Probably the most well-known tissue with poor/limited blood supply is tendons/ligaments - these are connective tissues with a lot of intracellular matrix made up of collagen, and blood supply to these tissues is poor the further you get from the source blood vessel as there is often very little collateral circulation (what it's called when an area has multiple arteries that feed the capillary beds).

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