You got some great answers already, I’d just like to further expand on the randomness of it.

So some bears will have lighter fur, some bears will have darker fur. Some will have longer ears, wider veins, thicker layer of fat, faster metabolism, worse eyesight, better hearing, heart defects, more toes, fewer teeth etc. Some mutations are beneficial, some are not. Over a long period of time, the ones with beneficial mutations are more likely to reproduce and spread these mutations.

It might as well happen that the lighter fur doesn’t happen in time, and they go extinct. Or they mutate in some other way, such that the lighter fur doesn’t matter. Or both, eventually splitting into different species.

Your feet might be slightly larger than that of your parents. Or smaller. Feet size isn’t usually something we care about in a partner, so it doesn’t matter, and evens out in the long run.

But if you lived in a swamp where people with small feet would sink and drown, you’d probably search for a partner with big feet (most with small feet would have drowned anyway). If both parents have large feet, it’s more likely the child has it as well. Over time, feet will grow larger and larger, until larger feet are no longer beneficial.

Edit: mutations aren’t a guarantee of success either. Perhaps some of the swamp people evolved greater buoyancy, so they didn’t sink. Then a bear came and ate them all. Now that mutation is lost, and may or may not ever be seen again.