Baer's Law states that in a given region, the number of species of mammals decreases as one moves from the equator toward the poles. This principle highlights the relationship between biodiversity and latitude, suggesting that warmer climates support a greater variety of mammal species. The law was formulated by the German zoologist Karl Ernst von Baer in the 19th century. It emphasizes the importance of environmental factors, such as temperature and habitat diversity, in shaping the distribution of mammal species across different geographical areas.