An interesting study from researchers at Auckland University suggests that molecular evolution happens faster in warmer climates. This in itself is not a novel finding, as the relationship has been found previously for ectothermic organisms -“cold-blooded” organisms whose body temperature is directly linked to climate. What makes this new study interesting however is that this relationship also appears to hold for warm-blooded animals. Because warm-blooded animals regulate their own body temperature, it was previously assumed that rates of genetic change in these organisms would be independent of climate.
The study measured the rate of evolution at a mitochondrial gene (cytochrome b) in 130 pairs of mammalian species, where one species in the pair occurs at lower latitude or elevation (warmer climate), and the other occurs at higher latitude (cooler climate). The rate of evolution was about 1.5 times higher in species found in warmer climates, and the results held even when the effect of differences in body size or population size were taken into account. Of course this study only used one mitochondrial gene (probably because of the availability of data for this gene across a wide range of species), and there are many reasons why what goes on in the mitochondria might not be the same as what goes on in the rest of the genome, particularly for factors likely to be associated with metabolic rate. So we can’t really say that species in the tropics are evolving faster on the basis of this result. But it will be interesting to see if this relationship holds across the rest of the genome.