There are a few bits of evidence that point to there having been a phase in human evolution in which we were mainly or partly aquatic.
First of all, you can take a look at aquatic mammals such as the seal and the walrus to give us a bit of guidance as to the characteristic adaptations to life in seawater that certain mammals have.
A layer of under-skin fat is found in aquatic mammals – think of whale blubber. This is present because fat is an insulator and water can quickly drain the heat away from the body – so this thick blubber layer helps preserve the body heat of mammals that live in the sea. Humans have a layer of fat under the skin – depending on how overweight they are, the amount of fat may vary, but it is there – so that’s the first piece of evidence.
When we are emotional, we cry. It is something that we take rather for granted, but it is also an adaptation of aquatic mammals to clean the eye from salt water – so that is another piece of evidence in favour of the aquatic ape hypothesis.
We are the naked ape – we are not covered with hair like the other apes are. However, we do have hair on our bodies – take a look! It is a reduced amount of hair, but it is there and guess what? If you look at the pattern in which the body hair grows – it grows in such a way a to streamline the body as it moves through water. Another strong piece of evidence.
However – we haven’t got to the clincher yet. When aquatic mammals dive into water, they exhibit the dive response, which is a lowering of the heart rate and redirection of the blood within the organism to make the best use of oxygen under the water. Yes – by now what’s coming next is obvious – humans give the dive response when they dive into water less than 70 degrees Fahrenheit in temperature.
Anyway, water seems to have an irresistible appeal for many. Where do a lot of people go on holiday? The beach must be at the top of the list – or why don’t you just relax by the pool? This may be some behavioural throwback to our aquatic past.
The evidence though seems conclusive – it is difficult to argue against the fact of the dive response – and the obvious, and fascinating, implication of an aquatic phase in human evolution.