As if we weren't flawed enough already......

"The real question," he says, "is what the evolutionary pressure of these therapies might me.  Would faulty genes become more prevalent, because they could be fixed?  I wear contact lenses, but if I were a caveman and my eyesight was as bad as it was when I was five, I would have been in serious trouble.  Now it doesn't matter.  We could replace our defective parts, live longer, and feel healthier."  Then he adds a provocative afterthought:  "Yet physically we could be much weaker and more flawed genetically."

-Diane Ackerman,  The Human Age:  The World Shaped By Us