Scientists explain how skink lizards “lost” their legs, and then got new ones

An international team of scientists has developed a theory explaining why the skinks living in the Philippines lost their legs during evolution and then regained them many years later. In a paper published in the journal Proceedings of the Royal Society B: Biological Sciences, the group describes their research on this tiny lizard.

One of the rules of thumb for evolutionary theory is that when a creature loses a complex structure (such as legs) over many years, it is highly unlikely that it will “return” to the descendants of the species. Now scientists have found a possible reason for this exception to the rule – the Brachymeles lizards, better known as skinks – lost their legs and then grew them back.

Previous research has shown that some of the skinks native to the Philippines once lost their legs as a result of evolution, and then for unknown reasons, their legs returned many years later. Other skinks living nearby also lost legs, but did not grow them back. In this new work, the researchers sought to understand why this happened to one group and not the other.

Captured skinks (those that re-developed legs and those that did not) performed various physical tasks, such as running in a tiny “racetrack”. The idea was to find out which conditions are best for using the legs and which conditions are better for moving in a snake style.

Researchers have found that skinks without legs are better at walking in dry conditions – for example, without legs, they are better at digging holes. On the other hand, skinks with legs (and feet) did better in wetter conditions. Their feet allowed them to move on wet ground. The researchers speculate that the skink’s legs appeared during a prolonged period of high humidity, and disappeared during a drought.