Most life forms, including the first unicellular organisms, evolved in tropical ecosystems. Even today, the Tropics harbor the great majority of species on Earth and provide an environment in which new species are most likely to evolve.
Over the eons, adaptation to a temperate or cold climate fostered more diversity as plants and animals dispersed across the planet, continents drifted toward colder latitudes and Earth's climate gyrated between periods of glaciation and global warming. Physical traits such as feathers, fur and fat insulation favored survival in the cold while some species developed behavioral adaptations such as migration, estivation or hibernation to survive in regions with a dramatic change in seasonal conditions.
We humans also evolved in the Tropics but, thanks to our large brains, were able to adapt quickly to colder climates without "waiting" for natural selection to control our expansion; the capacity to utilize fire, produce clothing and construct shelters fueled our dispersal across the globe. Nevertheless, climate change and its associated natural forces continue to challenge our welfare and how we adapt to global warming will determine the future course of human history.
