In addition to charles darwin, who also proposed a theory of evolution prompting darwin to publish his origin of species?

Alfred Russel Wallace, a biologist, naturalist and anthropologist who studied life in the tropics of Indonesia came up with the same idea of natural selection as Charles Darwin and prompted Darwin to publish his Origin of Specie sooner rather than later. He also studied the geographic distribution of species and as as well he was a social activist who criticized capitalism and warned of damage to the environment from man's economic activities.

Alfred Russel Wallace proposed ideas which prompted Darwin to publish his "Origin of Species". Alfred Wallace himself studied the distribution of species with respect to geographical conditions, and believed that there was some law governing the origin of new species, and it was not according to some predetermined pattern.
His paper, "On the Law which has Regulated the Introduction of New Species" was published in 1855.

Population size is the number of people in the population, whereas population density is the average number of people per unit of area/volume