Differential fitness is the third of Darwin's four postulates for natural selection. It states that survival and reproduction rates vary between individuals. Fitness differentals are widespread and detectable throughout nature. This fitness differential is visible in several ways, and it can be detected throughout nature. It can be based on behavioral differences that can act with or against environmental changes; one notable example was a 2014 study of snowshoe hares, where researchers found that white snowshoe hares did not change their behavior due to increased snow melt. Subsequent research found that brown hares survived and bred more than the white snowshoe hares. Differential fitness can also be applied between species. Researchers found that the Neotoma macrotis wood rat in the Cal