R/K reproduction strategies; how animal species and perhaps different human populations breed

It has long been known that animal species differ in their approach to reproducing. Some try to turn out as many young on possible and then invest little or no care in their upbringing. Others, such as the blue whale, have only one baby at a time and look after it well during its immaturity. It has been suggested that in humanity as well, different strategies of this kind are adopted by various ethnicities.