There's one situation where all apes are vertically oriented: when wading. There's a great talk by evolutionary anthropologist Elaine Morgan[1] that goes through all the weird aquatic mammal-type traits humans display.

[1] https://youtu.be/bFDqYzgJfIo?t=387

That's not really evidence though, is it? You wade because you want to keep the largest portion of your body dry and you want to be able to breathe. You swim when you have to or when you really want to, but you walk when you can. Wading is the better option in undeep water from an energy expenditure perspective as well, and likely safer than trying to swim in undeep water.

It's not proof, but it is evidence. It's not a smoking gun but at the same time, there are other peculiarities that line up with aquatic-ness: the hairlessness, the extensive subcutaneous fat, the breath control, the descended larynx, the swimming reflex. None of them on their own is proof, but combined they're difficult to hand-wave away. They're each traits that are very out of place in terrestrial mammals, and at the same time very normal in aquatic mammals.

I think they're all just super useful to have in a world where 2/3rds consists of water even if you predominantly live on the land. Note that there is no driving force behind any of this other than dumb selection and mutation and that it would be very strange to first lose all this stuff upon emerging from the sea but still living predominantly in coastal areas (as we still do today!) and then to re-acquire those traits over a relatively short period of time because suddenly they are pre-requisites for survival. Much easier to take them along for the ride where they are handy all the time, as evidenced by many other mammals that have all of these (and sometimes more).

But you're right in that in theory it could have happened and like any essentially unfalsifiable theory it will likely remain that way.

It's funny because depending on which field we're looking at I probably have my own 'aquatic apes' based on how solid I think a particular theory is but without dedicating a lifetime to it I'll just take the easy way out and align with the largest body of scientists until there is hard proof to the contrary. But in some fields the theories are known to be broken and then such discussions get a lot more interesting.

None of those are out of place.

aquatic animals (otters, beavers, could go on) have plenty of hair. Our lack of hair is function of avoiding parasites using our brain to protect our skin instead of fur armor.

All mammals have fat so I'm not going to get into that one.

All mamals have a swimming reflex, except even though most of them are not aquatic, their reflex actually works. humans that dont spend a long time to learn how to swim ... drown.

but there are features that are very much against us being aquatic: shellfish and fish allergies.

I think the "aquatic ape hypothesis" as originally proposed is a lot weaker than people in this thread seem to think. It wasn't a proposal that humans lived in the water, merely that:

> My thesis is that a branch of this primitive ape-stock was forced by competition from life in the trees to feed on the sea-shores and to hunt for food, shell fish, sea-urchins etc., in the shallow waters off the coast. I suppose that they were forced into the water just as we have seen happen in so many other groups of terrestrial animals. I am imagining this happening in the warmer parts of the world, in the tropical seas where Man could stand being in the water for relatively long periods, that is, several hours at a stretch.[1]

So, wading hunter-gatherers.

In this - as an primarily land based creature - wading seems reasonably effective.

[1] https://en.wikipedia.org/wiki/Aquatic_ape_hypothesis

Yes, and that's exactly what makes the hypothesis so unlikely, all this immense adaptation for something that seems to come more-or-less for free with a standard mammalian body plan. The timescales we're talking about for such invasive changes would be far longer than available for the whole of the aquatic ape hypothesis, but is recent enough that there should be plenty of fossil evidence. I just don't buy it, but if ever someone digs up fossil proof I'll be happy to eat a hat or two. It is roughly in line for me with 'Hollow Earth' and 'Water as a fuel'. It smacks of backwards reasoning and wishful thinking.

But: it's harmless and whoever wants to believe in it is obviously welcome to do so.

Consider that sea levels have changed considerably over the past ~5 million years, over which the Aquatic Ape (Hardy/Morgan) hypothesis might have occurred, and might be anywhere from 100 metres blelow current levels (putting fossils underwater at present) to 300 metres above.

Plus all the other usual challenges to fossil preservation.

That record is quite probably far more partial than appreciated.

<https://en.wikipedia.org/wiki/Aquatic_ape_hypothesis>

<https://en.wikipedia.org/wiki/Past_sea_level>

That said, I've no particular argument for or against the Aquatic Ape theory.