How fish evolved to walk – and in one case, turned into humans

When you think about human evolution, there’s a good chance you’re imagining chimpanzees exploring ancient forests or early humans daubing woolly mammoths on to cave walls. But we humans, along with bears, lizards, hummingbirds and Tyrannosaurus rex, are actually lobe-finned fish.
It might sound bizarre, but the evidence is in our genes, anatomy and in fossils. We belong to a group of animals called land-dwelling sarcopterygians, but vast amounts of evolutionary change have obscured our appearance.
We think of fish as expert swimmers, but in fact they have evolved the ability to “walk” at least five times. Some species pull themselves forward using well developed fore-fins, while others “walk” along the ocean floor.
Our sarcopterygian ancestor evolved lungs and other air-breathing mechanisms, bony limbs, and a stronger spinal column before venturing on to land. These adaptations were useful not only in aquatic environments but allowed our ancestors to explore land – they were “pre-adaptations” for life on land.
The water-to-land transition was one of the most significant events in vertebrate evolution. It may have started as a way to escape from predators, but the landscape our ancestors discovered was already rich with plants such as mosses, horsetails and ferns, as well as arthropods (millipedes) which had colonized land millions of years earlier.
How fish evolved to walk – and in one case, turned into humans