This is the question I have been working on of late. We know that stick bugs, for instance, are well adapted to blending in with their surroundings. The slowly evolved this defense mechanism over millions of years until it is pretty well prefected now. As the evolutionary timeline moved forward the stick bugs that looked most like a stick survived as the bright green stick bugs were eaten by birds. (This is a hypotheitcal scenario to make a point) Over time the ones that survived produced offsring more adapted to surviving and looked even more like sticks.
My question is then how can the 'bright green' humans survive just as well as the more adapted, better suited humans? We can all see everytime we go out that don't fit the human archetype. Excessively overweight, low intelligence, lazy, etc seem to get by just as well as everyone else. How can this be possible if things evolve through natural selection? It's simple; humans are not constrained by natural selection. The reason why? Technology. We are now the top hunters on the planet even though we wouldn't be able to hunt without technology. We don't succumb to the elements and weather because of technology. We survive virus and bacteria invasions because of technology. This means that everyone can produce viable offspring with the chance to carry on unfavorable genes unlike in the 'natural' world.
Being genetically predisposed to heart disease, for instance, would noramlly get phased out over time as the organism with that predisposition would produce less offspring therefore not passing on the gene as much until it no longer exists within the breeding population.