What two factors influence how strong the gravitational pull is between two objects?

In 1859, charles darwin published the first edition of on the origin of species, which explained his observations of various groups of animals that showed great similarities but minor differences. darwin concluded that if a population of one species separates into two different populations that live in separate locations, then over the course of many generations the different populations can develop into different species. this idea predicted many future biological findings and became the basis of modern biology. darwin’s explanation for why different species exist is best described as a(n) law. theory. inquiry. hypothesis.