"Survival of the least-fit".
Darwin would never have believed it.
"Fitness" is all about the environment in which the organism resides. Change the environment and the currently "fit" becomes unfit, and the currently "unfit" becomes "fit"
There was an interesting experiment that I read about long ago. Two types of bacteria were kept together in the same petri dish. As long as they were kept separated by centrifuge, they both flourished.
But when they were allowed to mix, in every instance one of the species disappeared. And in every instance, it was the same one.
However, it the temperature was altered a few degrees, or the pH altered, I forget which, the other species was wiped out instead.
Makes me think.
The definition of fitness changes.
During fat times, fitness is highest production of offspring. All survive, and more means more.
During lean times, fitness is highest survival rate of offspring producing individuals.
Darwin recognized that charity would help the crippled survive, but also recognized that it was our Christian duty to help.
What Darwin described as “suvival of the fittest” is actually about which individuals are able to reproduce more. Until recent history, the rich had more kids (both by wives and by mistresses) and the poor had fewer(because they starved).
In the absense of welfare, poor women would be working at taking care of the kids of the rich, instead of having a dozen of their own.