David Grinspoon, one of the scientists who in 2005 proposed that hypothetical organisms on Titan might use hydrogen and acetylene as an energy source, has mentioned the Gaia hypothesis in the context of discussion about Titan life. He suggests that, just as Earth's environment and its organisms have evolved together, the same thing is likely to have happened on other worlds with life on them. In Grinspoon's view, worlds that are "geologically and meteorologically alive are much more likely to be biologically alive as well".