Swim Bladder Evolution: Convergent Evolution in Fish

Convergent evolution

The swim bladder is a gas-filled sac that helps fish maintain buoyancy. Lungs are gas-filled sacs that help terrestrial vertebrates breathe. Although swim bladders and lungs share a similar function, they evolved independently from different ancestral structures. The swim bladder evolved from the gut, while the lungs evolved from the pharynx. This is an example of convergent evolution, which occurs when unrelated species evolve similar traits in response to similar environmental pressures.