The rise of a new species is actually a common prediction for the apocalypse, despite being one not often picked up on by the majority of end-of-the-world fiction. The more prosaic form is that an invasive species like the bullfrogs who ate everything in Australia in that one episode of The Simpsons could demolish our ecosystem, causing famine. Famine leads to riots, riots lead to starving, leads to death. The end. The much more terrifying other prospect is that some genetically engineered organism could be the one to topple our top spot on the food chain, which also mucks up the planet's balance. The other huge concern is actually a very tiny being: algae. The microbes that live on lakes, rivers and ocean floors are slowly evolving to the point that they could change Earth's atmosphere in such a way that there's not enough oxygen for humans to, you know, breath. The end of the world might be algae suffocating us to death.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/