Biodiversity describes the variation of life forms within a given species, ecosystem, or planet. The biodiversity of Earth tends to be highest near the equator as a result of the warm climate and high primary productivity in these areas. Rainforests are an example of this phenomenon. The period since the emergence of humans has displayed an ongoing reduction in biodiversity, called the Holocene extinction. At the same time, biodiversity affects human health in a number of ways, and the destruction of the planet’s resources could lead to a negative trend in human health.