Early life was unicellular, and we now know that it took just one random but crucial mutation, 600 million years ago, which changed the function of one key protein, to make multicellular life possible. In multicellular organisms, adjoining cells have to co-ordinate, and key to this at division is the orientation of the mitotic spindle, which segregates chromosomes into daughter cells. Using a technique called ancestral protein reconstruction, which is based on gene sequencing and computer modelling, Kenneth Prehoda of the University of Oregon, US, and colleagues tracked things back to a mutation in the GK protein-interaction domain (GKPID). Even more remarkable, the reason that a single mutation could have such a huge effect is a lucky resemblance between two seemingly unrelated molecules – so we’re lucky to be here at all.