As far as I know, humans are the only animals whose young may experience difficulty learning to swim.

Does this mean our ancestors are in fact aliens who crash landed on Earth thousands of years ago, and had to painstakingly rebuild (over the centuries) whatever civilization they had destroyed on the planet they had previously inhabited and then fled (perhaps like Khan [there's a cool video game there])?

Perhaps.

Although I imagine it's much more likely that as we've become more domesticated over the millennia, our young have lost some of the natural instincts that used to ensure their feisty survival in the wild.

Who knows?

😜