Which of the four postulates of Darwin's theory of evolution was not well established when On the Origin of Species was first published but is overwhelmingly supported today?

A) Some individuals in a population survive and reproduce better than do other individuals.
B) Individuals in a population differ physically from one another in many ways.
C) Individuals with advantageous traits survive longest and have the most offspring.
D) Some differences among individuals in a population are due to genetics and are heritable.