Humans like to believe that life is a very complex issue.
We imagine that all our relationships, our interactions with the environment and our success and failures must follow some sort of incredibly intricate and chaotic path, impossible to predict. Or perhaps it's the opposite. Perhaps we're incredibly simple animals, destined to go round and round according to a few simple rules. That sort of debate has kept philosophers entertained for millennia, but now science is also having a go at navel-gazing. Two separate studies in the US have drawn the conclusion that planetary life cycles are in fact much more simple than we ever imagined.