Interference with Evolution?

I've been thinking about this. We have been interfering with the evolution of many animals, but also our own.
A long time ago i read this book talking about what is evolution (i believe it talked a lot more, but this is all i remembered). They used lizards as examples. Lizard species X have two different colours. Bright orange and green. Bright orange allows predators to easily spot the lizards (disregarding other issues such as bright orange meaning the presence of poison etc), while green makes it harder. So it would mean that more green lizards would survive to reproduce, so as time passes the lizards with better camouflaging skills would survive and be able to reproduce, so species X, originally consisting lizards with 2 colours, would evolve into green lizards.
The reason why i linked this with the human evolution is that as our medical skills improve, more and more people with weaker immunity survives and reproduces, so it affects the evolution of humans. Originally, humans are suppose to evolve and have better immunity, but because our medical skills have improved, but because of our improved medical skills, human might not grow to have stronger immunity. And consider this also. In war, the soldiers who die are usually those healthy ones, for weaker ones are unable to battle. So stronger people actually have higher chances of dying.

So stronger people die, and weaker people survive. What will humans evolve into?

This is just my personal thoughts. I am not saying that we should not improve our medical skills.