Back in the days of killer newts the size of cars, swimming for fun wouldn’t have been a priority. But Metoposaurus algarvensis, the fearsomely toothy and giant ancestor of newts, rampaged in the Triassic period long before humans or anything resembling our ancestors existed. When you see tiny-toothed smooth newts (Lissotriton vulgaris) small enough to sit in the palm of your hand you are looking at a creature with ancient lineage, older than dinosaurs.
Amphibian means both kinds of life. Smooth newts have two separate stages of life in two different environments; as tadpole-like larvae restricted to life in water, and then as newts that can go on land. Adult smooth newts oscillate between terrestrial and aquatic life. Except occasionally smooth newt populations exhibit two forms of maturity. Some individuals are paedomorphic; they never progress to terrestrial dwelling and remain in the form of aquatic larvae but reach sexual maturity. While others follow the standard progression from immature water-bound larvae to mature newts that can go on land. Two forms of maturity provide an adaptive strategy that allows smooth newts to take advantage of auspicious living conditions. When water bodies are rich in nutrients and free of predators it is advantageous to remain in aquatic larval form. But if the aquatic environment becomes more hostile, for example if fish are introduced, paedomorphosis disappears and mature newts are all terrestrial.