So, the aquatic ape hypothesis is more maligned in recent times because of the whole mermaids fake documentary shit that came out. Before that though the hypothesis poorly attributed various traits to aquatic evolution and in a way that's pretty poor. Namely, from what I remember, it proposed the following:
- Our reduced body hair is an adaptation for swimming for better hydrodynamics.
- The placement of our nose facing downwards is to better be able to swim, as nostrils facing forward like other apes would fill up with water
- Our less dense bodies make more sense for swimming
- Our ability to give birth in water and have babies hold their breath and swim for the surface is """evidence""" of our aquatic origins
- IIRC sweating was supposed to be a measure to get excess salt out of us, like how some reptiles have salt glands to expel excess salt
- The layer of fat beneath our skin being like blubber
There are a number of problems with these points though.
First off the reduction in body hair is actually a poor adaptation for animals our size to adapt to water. You see this best in seals and otters, although the original theory iirc compared us to whales and hippos(much bigger animals). Seals and otters actually have
MORE hair per square centimeter than most land mammals. This is because their dense fur actually traps air between their hair and skin to act like insulation, which is more useful for smaller, warm-blooded animals in the water all of the time. The
square-cube law means that smaller animals have a larger surface area relative to the heat producing tissue, thus they lose more heat relative to how much they can generate it. This is bad if you live in the water all of the time and humans can and will die of hypothermia in even fairly warm waters if they're left in those waters constantly.
For the seals and otters, same with penguins too actually, this does not cause any real issues with drag. When the fur or feathers are so dense like this they avoid creating much turbulence(thus the drag) and instead act more like one solid and largely smooth surface.
Secondly the placement of our nose has more to do with the changes in the shape of our skull and jaws. Humans have had a major reduction in the size of our jaws and this has led to the nose pointing downwards more. However the placement of our nose is not to the benefit of this hypothesis as most diving animals who spend the majority of their time in the water develop nostrils that close, whilst we lack those. Here's a nice picture showing off why our noses point more downwards.
Thirdly our less dense bodies make more sense in the context of travelling over larger distances, which fits with how some of the most primitive human populations were observed hunting and how some human populations still hunt via
persistence hunting. A denser body costs more energy to move over a larger distance. Bipedalism is actually advantageous for this too as exhaustion is also a factor in persistence hunting and running/walking on two legs is more energy efficient than doing so on four.
Fourthly the ability to give birth in water is not unique to humans. It's part of the
mammalian dive reflex and is exhibited by a lot of other mammals who don't spend any considerable amount of time in water.
Fifthly sweating is far better explained with the persistence hunting mentioned prior. Sweating allows us to quickly lose heat via
evaporative cooling, which is essential when you're trying to basically get another animal to die from heat exhaustion/stroke. Sweating only accumulates salt outside of the body in the sense that it excretes water at about the same salinity as that of the water in your body and it can not be recovered, nor can the water. This makes sweat a very poor adaptation to dealing with the saltiness of the ocean as you're not conserving water whilst purging sweat, thus making the ingestion of seawater a losing game.
Most mammals who evolve to live in the oceans or to drink sea water usually evolve better kidneys to be able to do this. In the case of whales and dolphins they actually get a good amount of their water from their prey whilst also having their powerful kidneys. This also relates to the whole hairlessness thing as our bodies are very well adapted to lose heat, not retain it. Thus why we have long limbs and not-so-stocky abdomens and chests. People who've evolved in colder climates tend to be stumpier and more stocky.
Sixthly the layer of fat beneath our skin is not like blubber at all. Its insulating ability is terrible. Real blubber is dense, thick, fatty tissue that is poorly vascularized. Our skin however is quite vascularized, as again we evolved to get rid of excess heat and not to retain it. Our layer of fat beneath the skin is also quite thin.
All of that said though, our ancestors did make more and more use out of aquatic resources but this would've been at either around the time of Homo Erectus or afterwards(I remember some of the earliest evidence being with Neanderthals and modern Homo Sapiens), thus after our most notable features that the hypothesis proposes evolved. What features we have that are useful for aquatic lifestyles are thus
exaptations. Exaptations being adaptations that were originally evolved to deal with one issue but proved to be useful for a new issue that they were then made to deal with.
An example would be an animal having green skin to camouflage itself and then being put into an environment where the color green attracts a kind of prey, but to which there is little green around for them to hide. The original adaptation is useful for its original purpose but has a useful purpose in this new environment but via a different method.
wtfhappenedin1971.com
