Water is ubiquitous. Water falls from the sky, collects in creeks, rivers,
lakes and oceans. Some places are covered with water for half the year.
Humans can't survive without it - neither can any other species on this
planet. Since many terrestrial predators aren't opposed to eating aquatic
animals, and many terrestrial herbivores aren't opposed to eating aquatic
plants, I don't think that because we eat aquatic animals regularly that it
means we went through any "aquatic phase".
Yes, humans have less hair, but so do a few other terrestrial mammal
species. And, generally, when a mammal species evolved towards aquatic life,
hair was not the first thing to go. Look at seals and sea lions - only
walruses and elephant seals are hairless, and that group has been at it for
millions of years; and what about otters? river-rats (nutria)? beavers?
various shrews? Of course they aren't primates, but they are extant species
that are observable (unlike generally hairless fossils).
The growth pattern of human hair resembles the growth pattern of most other
mammal species' hair, and it's not for swimming, it's for streamlining.
After all, it wouldn't be good to be an antelope with back hair growing
forward (imagine the wind resistance), or a rat with it's back hair facing
forward, the brambles!. For another thing, it's hard to groom your fur when
the growth pattern faces the area you lick from, and it's a rare mammal that
doesn't groom itself.
Human babies aren't the only babies that have a swimming reflex at birth -
all other primates do as well, and, so far as I know, all other mammal
species do. This swimming reflex disappears after a few weeks, and the young
creature will drown after that time when placed in the water. Reptiles tend
to retain the swimming reflex from birth to adulthood, even species that
live in very dry areas. Even birds have a swimming reflex, if you can call
it that.. they tend to flap in a fashion that keeps them above water -
hopefully long enough to find a dry spot. It's easy to look up on the 'net,
but I know Discovery did a show on it and showed scientists doing
experiments with human and animal babies.
Developing a fatty layer when exposed to conditions that strip the body of
it's heat makes sense, and constitutes no evidence that we, as primates,
were ever aquatic. The human body develops all sorts of adaptations to
different circumstances. For example, people living at high altitudes tend
to have larger lung capacity - does that mean we went through an "oxygen
starvation" period? It would be interesting to see if other terrestrial
mammals that occasionally swim, when swimming more often than usual also
develop a fatty layer. I'd bet my money that they do.
Just about everything I read on the subject points to the enlargment of
breasts being a sexual signal, and nothing more. Some women have large
breasts, some women have very flat chests (though most women are
in-between). If this were a survival adaptation, wouldn't ALL women have
breasts "designed" for water-life? Breasts aren't testicles, milk glands
don't require cooler temperatures to make milk (and water strips heat
quickly), and human babies, as someone already mentioned, need warm milk
when they are born and a few weeks thereafter. I agree with Todd, it makes
much more sense that breasts are sexual signals derived from buttocks - and
every straight man I know agrees.
Why would downward-pointing nostrils help anything as far as water life?
When I swim, I find them a nuisance rather than a help. All other truly
aquatic species have nostrils that point UP. Ever see swimmers turn their
head from side to side? That's so they can breathe.
Of course, if you want to get right down to it, every animal on the planet
went through an "aquatic period", it's called Precambrian and ended about
544 mya. You could extend that to the Silurian (only 410 mya) if you only
consider "significant" terrestrial life, like the first land plants.
-Ellie
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