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GeriatricHydralisk t1_j9gpv7o wrote

Rather than cover what's already covered elsewhere, it's worth pointing out why the AAH fails:

  • First, it considered traits "piecemeal", rather than looking at the organism as an integrated whole. This allows it to engage in the common fallacy of "remembering the hits and forgetting the misses" - it points to things like the diving reflex or subcutaneous fat that are consistent with diving, but "conveniently" ignores traits completely inconsistent with aquatic life, such as lack of reflexive swimming (babies show a diving reflex, but cannot actively swim) or valvular nostrils.
  • Second, it's completely at odds with comparative data. Lots of mammals have become semiaquatic and aquatic, and none of them have done so in the manner postulated by AAH. Nostril valves and webbed digits are near-universal in semiaquatic mammals, but absent in us, nothing else has become bipedal to move in water like AAH proposes. There are even several monkeys which swim and dive on a VERY regular basis (Allen's Swamp Monkey, Japanese Macaque, Proboscis Monkey), and a) don't display anywhere near the strength of adaptations claimed by AAH and b) have the sort of adaptations you would expect from a typical swimming/diving mammal.
  • Lastly, back when AAH was proposed, and when all the major books/articles/talks in favor of it came out, we knew almost nothing about our ancestors, particularly their habitats and ecology. The Leakeys had only just begun their work, and wouldn't find Lucy until the 70's.

Getting dragged into the particulars of this or that trait is a mistake, operating on too low of a level. Considring organisms are integrates wholes, and considering trait evolution in a comparative context, AAH makes not a damn bit of sense.

It's also why nearly nobody with a PhD in a relevant field takes it even remotely seriously, and the only exception was a plankton ecologist with no training in anthropology.

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KEVLAR60442 OP t1_j9gq5m5 wrote

Thank you. This thoroughly helps my understanding.

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Marsdreamer t1_j9hn9fl wrote

Adding to this, no evolutionary biologists look at traits in organisms today and explain how / why they evolved by how they are beneficial. To do so is teleogical, explanation by the purpose they serve rather than the process by which they came to be. It also ignores that sometimes traits serve no actual purpose. They can arise to fixation randomly or the trait is vestigial for some other functions that are no longer relevant, but now serve a different purpose. A good example is that, in the case of human hairlessness, the reason why is still actually a pretty hotly debated subject because we don't really know.

Generally speaking, in order to confirm a trait's purpose and evolution you have to study the impact on fitness when you remove that trait and you have to use nearest relatives or most common ancestors to show how the trait evolved in the model species in question.

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_The_Librarian t1_j9hoe30 wrote

For anyone like me that doesn't know, 'teleological' means "Relating to or involving the explanation of phenomena in terms of the purpose they serve rather than of the cause by which they arise."

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Lets_Go_Why_Not t1_j9hoxtq wrote

Sexual selection complicates attempts to explain certain evolutionary changes - sometimes, a trait just becomes more attractive to the other gender and, while that trait may represent an underlying superior fitness (beyond the obvious “can have more babies because I’m more fuckable than others”) it also may not. It’s possible that early humans just decided they weren’t down with hairy boning so much.

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[deleted] t1_j9i08eb wrote

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Marsdreamer t1_j9i2pi4 wrote

Not always. There's a great example of an evolutionary study on a bird species that had incredibly long tails. Like, tails that were so long that they often interfered with flight and made the bird significantly more likely to be caught by predators.

However, the females preferred males with longer tails. So, what essentially happened is that the male birds continued to grow their tails as long as they possibly could until they hit a sort of critical threshold of being maximally attractive for females, but juuuust short enough that it didn't completely hinder their ability to get away from predators and fly.

Researches assayed this by taking feathers and artificially elongating certain male bird's tails (basically bird hair extensions). They noted that these doctored birds had significantly higher mating rates than other birds, but on the flip side, they also got caught (and killed) by predators much more often.

There's tons of examples of this throughout nature, where sexual selection essentially overrides the fitness loss for 'deleterious' traits.

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kamintar t1_j9iwty4 wrote

You explain this so eloquently and clearly, the mark of true knowledge. Thanks for sharing.

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Lets_Go_Why_Not t1_j9i1ik4 wrote

They certainly can be, for sure, though sometimes the mechanisms can be blurred - for example, is a sexual preference for greater height in place because taller people are inherently better at something because of the height OR is it simply that people with access to sufficient food and nutrients (through a variety of mechanisms) are taller, thus height is just an indicator, rather than a survival mechanism itself. And that doesn’t even begin to account for sexually selected traits that are theorized to be technically detrimental to day-to-day survival BUT that kind of indicate to potential mates “if I can afford to waste energy on this useless trait, imagine how awesome I am in everything else!” (eg peacock feathers).

In other words, sexual selection can be weird to untangle.

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hugthemachines t1_j9ixhfq wrote

That is very interesting considering how often I hear people explaining attraction for certain attributes connected to better survival of the off spring.

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Lets_Go_Why_Not t1_j9iywvl wrote

Ultimately, being able to attract the interest of a partner is directly connected to better survival in that offspring that are actually born have a better chance of surviving than those that never have the opportunity....it's just the thing that attracts that partner may not contribute to survival after they are born.

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codyish t1_j9idhaz wrote

So much this. I can't believe how many highly educated and smart people, some in biological sciences, can't accept that many traits appear for no reason and don't disappear because they have no reason to. My advisor used to say, "evolution doesn't have to help you to happen; it just can't kill you or make others not want to fuck you".

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CarpeCol t1_j9j6djk wrote

There are some traits that have no impact on survival or reproduction, but are expressed because the genes for that trait are found very close to the genes for another trait that does impact survival or reproduction. This can result in the first trait being passed to the next generation along with the second trait.

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danby t1_j9jy3dw wrote

A problem here is how we teach evolution; that traits (and by extension) genes are selected. But the reality is in any given environment only a subset of traits are under active selection pressure. Most genes are free to drift by chance and appear and disappear.

I have somewhere of the order of 20-24k genes. I live in an environment where we estimate that 2000-4000 humans gene show adaptations to settled agriculture and cities. Less than half of human genes are estimated to be house keeping (i.e. required by all cells)

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punninglinguist t1_j9ilw5a wrote

Can you give some examples of the kinds of explanations that are still accepted in the field? Like, "Here's a trait that [some animal] has. Here's the uncontroversial scientific consensus on how it evolved."?

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avcloudy t1_j9iyv30 wrote

This is going to feel a little bit targeted, but it’s important: understanding is a story we tell ourselves that feels satisfying. Explanations being plausible contributes nothing to their truth value. The poster above goes over it briefly, but the correct way to test an aquatic ape hypothesis is to look at the adaptations other animals who are aquatic/nonaquatic have and compare. Looking at our adaptations in a vacuum and trying to find an explanation, even if you aren’t picking and choosing is bound to find just-so explanations that are plausible but nearly certainly wrong.

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Tuga_Lissabon t1_j9hg6b4 wrote

Good explanation there.

Losing one's fur is also useful to lose heat, which also fits the persistence hunter theory.

Just looking at a few traits isn't going to give the full picture.

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Snizl t1_j9ipjkc wrote

This so much. I was wondering the other day about how humans conquered the coldest climates for millions of years, but never regained any fur to brace themselves against the cold. Until I went for a hike in the snow and quickly had to remove my jacket at - 10C because damn, bodies produce a lot of heat when moving.

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ukezi t1_j9is0a4 wrote

Plus once humans left the really warm area we seem go have had figured clothing out. Covering yourself in the fur of the animals you hunt is more efficient then growing that fur yourself.

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MonsieurReynard t1_j9jahu0 wrote

The evolution of language trumped all other adaptations. Houses and clothing and controlled fire followed soon thereafter. From then on, human evolution cannot be understood without considering culture.

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miparasito t1_j9ip6wl wrote

Are there any other hunting mammals that have lost their fur?

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mere_iguana t1_j9iqu4j wrote

This theory relates to persistence hunting in particular. Losing fur would not be useful for any other type of hunting.

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PhuckBigMoney t1_j9jpgs1 wrote

Are there any other hunting mammals that have learned Calculus?

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MrDBS t1_j9jvhwd wrote

This is why I don't change my rate of speed when a squirrel jumps in front of my car. I am willing to let them learn algebra, but not calculus.

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kelroe26 t1_j9hbrcr wrote

I know people on the internet normally say this sarcastically, but I mean it with all sincerity. You must be a lot of fun to talk to at parties! That's a really cool and concise delivery of some very interesting information. Thanks, Queen/King

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ExaltHolderForPoE t1_j9hkzv1 wrote

With knowledge like these, OP doesnt go to parties..... parties goes to him.

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Tarantio t1_j9ix1oy wrote

Are there any traits that we can say are linked to humans' propensity to swim?

I know that humans (and most apes) have no instinct to swim, but humans do learn to swim and enjoy doing so. We've also been fishing for a long time.

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GeriatricHydralisk t1_j9jfnpm wrote

Not as far as I know, though there are populations of humans who dive a lot (the Bajau sea people) who have enlarged spleens and several other differences in their blood. However, these people spend huge amounts of time foraging and diving in the water, and have for thousands of years.

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Tarantio t1_j9ji7y0 wrote

I'm thinking much longer ago than that, if homo habilis tools have been found mixed among fish fossils: https://www.wired.com/2010/06/first-fish-diet/

I don't know how one would go about determining what adaptations allowed early hominids to catch fish.

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GeriatricHydralisk t1_j9jklgp wrote

To be fair, though, catching fish doesn't necessarily mean swimming or diving. With a good spear and some practice, you don't even need to go knee-deep.

The other problem with extensive aquatic behavior in early humans is that basically every body of water in Africa bigger than a puddle probably has at least one Nile crocodile in it. That doesn't preclude aquatic behavior, but certainly discourages it.

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[deleted] t1_j9isipc wrote

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GeriatricHydralisk t1_j9jejqa wrote

Everything I wrote is against AAH. An idea can be wrong even if we don't 100% know the right answer, because we know that particular answer doesn't fit the data.

Think of it like the boardgame Clue. I may not know the answer, but when my friend guesses Col. Musrard in the library with the candlestick and I have all those cards, I know my friend's answer is wrong.

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[deleted] t1_j9h6kkw wrote

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