As compared to the great apes, their nearest living relatives, humans exhibit many significant differences in anatomy and physiology, including bipedalism, almost hairless skin like some marine mammals, hair growth patterns following water flow-lines, increased subcutaneous fat for insulation, descended larynx, vestigial webbing between the fingers, vernix caseosa, a hooded nose, muscular nostril aperture control and the philtrum preventing water from entering the nostrils, voluntary breath control like marine mammals and birds, and greasy skin with an abundance of sebaceous glands, which can be interpreted as a waterproofing device.*
(No mention is made of it here, but subsisting on a diet of shell-fish is also adduced as facilitating a leap in brain size: granny was right about the benefits of fish. The first human journeys, through which the species colonised the planet, also appear to have been made along coasts).
The hypothesis's attraction for me is quite personal. I find it impossible to relax fully on holiday without water and sunshine. Warming up, whilst stretching out with a good book, alternated with frequent dips to cool down is a sine qua non of hols.
It's obviously not just me either: isn't it striking that as soon as man had the material and technological ability to do so, he (and wife and kids) vacated to a sunny, little sandy inlet (or its equivalent)?
I guess it's a bit like that brilliant Ken Russell film Altered States: as we get on the plane or cross the water we're preparing to make the (sometimes traumatic) reversion to a primaeval coastal past. Palms itch, perspiration breaks out, feelings of seediness and fatigue almost overwhelm. Then, arrival: strip down, jump in, wallow about: back to our true state of nature. The addition of fresh seafood and a form of fermented fruit juice helps too.
Here I am emerging from my hotel bedroom on a recent seaside trip:
* I'm persuaded by the 'weak' version - hanging out in rock pools for a few thousand years - more convincing than the 'strong', which posits we lived almost amphibiously, otter-like.