The earliest primates were probably insectivores. They produce altricial offspring requiring a long time to maftire. R-selected species reproduce quickly and have many offspring. They produce many precocial offspring that quickly mature. A model of the evolution of cooperative behavior.
Individuals help relatives because relatives share genes.
By helping relatives to survive and reproduce, individuals are helping perpetuate copies of their genes. Do not confuse kin selection with group selection. In polygynous species, females tend to be more picky in choosing mates while males are less selective. Mating relationship between one male and one female. Male and female reproductive variance is approximately equal.