Evolution caught in the act

Different mutants of Arabidopsis thaliana. Image: Detlef WeigelUS-German team measures how quickly genomes change

Mutations are the raw material of evolution. Charles Darwin already recognised that evolution depends on heritable differences between individuals: those who are better adapted to the environment have better chances to pass on their genes to the next generation. A species can only evolve if the genome changes through new mutations, with the best new variants surviving the sieve of selection.