The majority of the cells in your body are not human cells. But these microbes all work together to make you one complete you. What if the Earth worked in the same way? That is the basis of the Gaia hypothesis. This hypothesis is the idea that the planet Earth is one single living organism; all of the humans, animals, plants, and everything non-living on Earth all make up "Gaia." British scientist James Lovelock developed this hypothesis in the 1960s when he was working with NASA on methods to detect life on Mars.