Evolutionarily, our only reason for being here is to further the species. When we reach sexual maturity we are at our prime to further the species, after we pass that point, we start to slowly shutdown. Hormones are the chemical instructions that tell us how to grow, burn our fuel, shift gears in fight or flight ( stress ), repair our bodies, etc. So evolution says - good job with procreation, now you are a drag on the species. So as Rutger Hauer on Bladerunner says "time to die". Lowered and changed hormones is evolutions way of getting us out of the way to further the species.
The point is, this is a biological process, not a social one.
Natural Laws are not real laws, just an empirical look at certain phenomenon that are open to interpretation.
This whole conversation is really a huge sidenote so I will not go on about everything you wrote, but as thinking beings we choose to either help others - or not, sometimes this agrees with evolution some times it does not. In effect, with our technology we are actually modifying evolution. But the minute we lose our technology, civilization and compounded intellect, unencumbered evolution will again take over.