How would Darwin explain the procreation rate differences between social groups?
His theory remains intact. Those ‘species’ that need to reproduce to the max do so to ensure survival in a harder world where chances of longevity are reduced. (i.e, cats/ mice etc) Those species who are physically stronger, including us, breed less frequently, i.e elephants. Basically, middle and upper class people are in a financial position in an elevated and humanly artificial manner to control birth rates because they are affluent and educated enough to do so, whereas the trailor park example you give, generally and stereotypically, only function to reproduce as that is the only cherished goal within their societal orbit, basically, one can have a child and succeed at the ultimate goal for all human beings once we are not distracted or fooled by personal goals, as in a career or education. This is not to say one is better than the other. As childless and educated myself, I envy having a child because all else is ultimately futile and self bound and meaningless in the final analysi