I just want to say that my son is pretty bad at swimming.
I quickly add, for a 3 year old human, he’s pretty darn good at it. Amanda’s family is very aquatic, as tends to happen when everyone spends several weeks per year (or longer) on the edge of a lake. They can all ski really well, they can all swim really well, etc. etc. So, very soon after my son was born, his grandfather started to bring him to age-appropriate swimming lessons. He is now 37 months old and has been to a swimming lesson almost every week. In addition to to that, Amanda brings him to the pool pretty close to once a week, often more. In addition to that, during the summer, he has spent several days at the lake and gone in once or twice almost every day the conditions allowed. In short, he should be about as good a swimmer as any 3 year old.
And he is. In fact, better. He is far beyond his age to the extent that he’s skipped grades, and the people at the swimming school have to keep making adjustments in order to ensure he is always getting the next level of training rather than being held back by the other kids who are not as good as he is.
But still, this means he can drag himself underwater for several bananas (the unit of time used by swimming instructors, apparently), and he can thrash around moving his body across the surface several inches in a predetermined direction. He can get himself to the bottom of a pool as deep as he is tall and easily pick up a ring or some other object, and he can float around in various positions comfortably.
So he swims better than a new born through 1 month old hippo (they can’t swim at all, really) but he’s nowhere near as good as dolphin. But the thing is, this is after three years. Had Amanda and I been aquatic apes, my son would not have survived to this ripe old age. The diving reflex, proffered as evidence for an aquatic stage, during which we spent considerable time in (not near, in) water, happens in mammals generally and alone is not enough to count as a retained adaptation suggesting an earlier evolutionary stage. If human ancestors subsequent to the split with chimpanzees went through a significant aquatic phase (not just living near water, which is one of the backpedaled versions of the AAT) then our children would probably … not necessarily but probably … be much better at swimming than they are.
This does not disprove the Aquatic Ape Theory. Nor does a single nail secure a coffin. But it certainly does not inspire confidence in the idea.
My son tells me that he plans, someday, to teach me to swim.