What is the evolutionary purpose or explanation for a California sea lion's tail?

Question

Otter's have a tail that helps with swimming, but a California sea lion's tail is a small nub that couldn't help with swimming or supporting the sea lion. Why is it still there?

Answer 1

Evolution is a slow process. So a feature doesn't disappear the *instant* it is unnecessary. It will take millions of years for an unnecessary feature to disappear completely ... and even then the genes will still be present (though unexpressed) and may be expressed in the embryos (the way the human tail and even gill folds are temporarilty expressed in human embryos).

[As other examples: humans and the other tail-less apes also have a "tail nub"; dolphins and whales have vestigial hip-bones that serve no purpose; dolphin embryos have leg buds; some species of pythons have tiny leg buds that serve no purpose. For *lots* more examples, Google "vestigial structures."]

That is precisely why these things are evidence of evolution, rather than spontaneous creation. Evolution explains these features as remnants from ancestors, remnants that have not fully disappeared ... whereas spontaneous creation has no explanation for why a creator or "intelligent designer" would include these useless or (at best) less-than-optimal features in the design, or cause them to appear temporarily in embryos and then disappear by full development.

Answer 2

Their tails are not small nubs. They are fin-like and help with swimming and with pushing them around on land.

But you are looking at evolution incorrectly. Animals don't develop features to fit a purpose. They deveop features first and if those features are useful, they can reproduce and survive. If the features are useless, they are less likely to survive and reproduce than another individual with a more useful feature.

I'd say that the tails off the California sea lions are just fine for surviving up to a point. But perhaps they will eventually become extinct because their shape does not permit more efficient swimming and make it so they have to spend a lot of time on land. I don't know which species they compete with for food and habitat. Perhaps dolphins. Maybe dolphins are a more suitable form for aquatic mammals.

Answer 3

Maybe just to use as protection for the anal passage? Consider that it might be an easy entry point for parasites if unprotected.
Or it might be vestigial like our tail bones.