Natural selection has, for all intents and purposes, been stopped dead.
We help the weakest to live, we have the stupidist among us producing the most offspring, and the smartest among us producing the least. As thomsbrain points out, those of us with severe eyesight impairments are given the ability to live to reproduction age. The same with mentally and physically deformed individuals.
<< Technology improves just as causes of disease and ill-health increase. >>
Um, did you pull this out of your ass? Becausre there has been no increase in the causes of disease or ill-health. In fact, our life expectancy continues to rise (even in third world countries), not fall.
We live longer, and therefore have a greater chance of contracting different diseases, but the number of diseases has not increased signifigantly. Old ones go away, and new ones crop up. Germs and viri evolve much like we do, but at a much faster rate. Technology has done little but help us live longer, so we have more of a chance of contracting a disease. Cancer is a good example. The overwhelming majority of cancer cases occur in patients who, just 100 years ago, would be far past the average life expectancy. But today, they live long enough to get it.