Asexual reproduction (Splitting)

The first form reproduction began about 4 billion years ago, when first RNA molecules and then DNA molecules began to make new copies of themselves by letting amino acids hook on to parent molecule and then splitting them off. All reproduction since then has been the same thing DNA molecules making more of themselves-only the DNA molecules have envolved more and more complicated ways to protect themselves and help the process along.

Questions:

1. If asexual reproduction (clone) is natural why it is negative in humans?

Some days ago I was investigating about the problems about the clones. I found that, the humans clones have more probability to have deformations and deseases, so it can cause rejection between the species.

2. What could happens if humans clone?

If all the humans are clones, can cause the extintion of our species, because the scientists think that the clones are not gonna last so much.