Evolution at work

A marine iguana hunkers down in the swell to graze seaweed from a rocky reef in the Galapagos Islands. Only the males can dive down to the shallow reefs, while females and smaller males forage in the intertidal zone. A protected species, it’ s only possible to dive with them at one site in the Galapagos. Researchers theorise that the iguanas arrived there from Central America by floating on rafts of vegetation washed out from jungle rivers into the Pacific. There are at least seven distinct subspecies of marine iguana populations across the archipelago. Photo by Simon Rogerson