they say that the human race came from a headless, hermaphrodite mollusc. It may be hard to imagine, but it is believable. Life started in the very deepest of the ocean, there is no light and very little oxygen. In the ocean new life forms are coming into being all the time. Some will move up a level in the ocean (closer to the surface), maybe to a level where they may need to see to ensure their survival. Some of these new life forms will die out as they cannot adapt, some of them may even go back down a level. While one of the life forms will adapt and be able to survive at the new level.
If you were to keep a family in constant darkness for a few generations the children would start to be born blind. Of course, this has never been tested on humans, at least not to my knowledge.
I see life as a race, a race for survival. Every single life form needs another to feed from. Even plants will quite happily feed from remains. New germs can appear as though from nowhere, an animal virus that can mutate to infect humans, this is evolution. The virus evolves to include us in it's meal chain, we become a NEW means of survival for this living thing. It has adapted, learned, and then evolved the physical traits necessary for long-term survival.
We are still evolving too. Our bodies may well have slowed down, but our attitudes and even our minds are evolving. The future looks bleak, particularly with the global warming threat, many of us will die off. The world is changing, and an individual will not be able to evolve the necessary traits to survive... but his children will, and his childrens children, etc. You never know we may all start turning black again. It's a possibility, as the sun increases in strength, our childrens melanin will need to increase to protect us from the sun. Also, nostrils will need to widen so that we can breathe the thin air better.