Answer:
Imunizations
Step-by-step explanation:
Humans don't care about natural selection so they just say, Oh lets make every fit so everyone can live and happly ever after, if only that where how it worked. People or at least some people with health problems have genetic deficiceis, meaning they are less adapted the to envirornment, then they pass on those genes and vola you have a desperataly unhealthy sociaty, humans take compasion to far. Of cource modern sociaty hasn't been around long enough to greatly affect the gene pool, most of that is purly from our lugerios lives