The Vital Question: Why is life the way it is?

by Nick Lane

Sex is needed to maintain the function of individual genes in large genomes, whereas two sexes help maintain the quality of mitochondria. The unforeseen consequence was that these two genomes evolve in totally different ways. Nuclear genes are recombined by sex every generation, whereas mitochondrial genes pass from mother to daughter in the egg cell, rarely if ever recombining. Even worse, mitochondrial genes evolve 10–50 times faster than genes in the nucleus, in terms of their rate of sequence change over generations, at least in animals. This means that proteins encoded by mitochondrial genes are morphing faster and in different ways compared with proteins encoded by genes in the nucleus; yet still they must interact with each other over distances of ångströms for electrons to transfer efficiently down the respiratory chain. It’s hard to imagine a more preposterous arrangement for a process so central to all living things – respiration, the vital force!