LONDON.- They might not have legs, but snakes are outpacing their relatives in the race to evolve.

New research reveals that snakes evolve up to three times faster than lizards as they develop new ways of feeding, moving and sensing the world around them. This burst of evolution appears to have started soon after the reptiles became recognisably snake-like, and continues to this day.

Professor Daniel Rabosky, the senior author of the research, says, ‘Snakes evolved faster and, dare we say it, better than some other groups. They are versatile and flexible and able to specialize on prey that other groups cannot use.’

‘Fundamentally, this study is about what makes an evolutionary winner. We found that snakes have been evolving faster than lizards in some important ways, and this speed of evolution has let them take advantage of new opportunities that other lizards could not.’

Dr Marc Jones, a co-author as well as Curator of Fossil Reptiles at the Natural History Museum, says, ‘The study really highlights the differences between snakes and legless lizards.’

‘Being limbless is a great way to avoid being seen by predators and prey, but it’s striking how snakes have diversified so much compared to limbless lizards.’

The findings of the study were published in the journal Science.

Why are snakes so successful?

Snakes and lizards, together known as the squamates, make up around a third of all land-living vertebrates. Their success means there are around 4,000 species of snake alive today, living all manner of different lifestyles.

Snakes have evolved to climb, glide, swim, and burrow underground. Different species eat everything from snails to animal carcasses, hunting with strategies ranging from venom to constriction.

While previous research has shown that snakes were able to rapidly bounce back from mass extinctions, like the one which wiped out the dinosaurs, this doesn’t explain why the animals are so adaptable.

It’s a particular puzzle when the success of snakes is compared to that of the lizards. Lizards aren’t doing badly – there are many more species of lizard than snake - but while snakes continue to evolve, giving rise to new species, there are some lizard groups that have stayed pretty much the same for millions of years.

Some of these lizards even look like snakes but haven’t experienced the same success, adding further to the puzzle. To try and solve it, the researchers sequenced the DNA of over 1,000 squamates, and combined this information with data gathered from studies out in the wild and in museums.

Dr Pascal Title, one of the study’s lead authors, says, ‘Museum specimens give us an incredible window into how organisms make a living in nature. For secretive animals like snakes, it’s almost impossible to get this kind of data any other way because it’s hard to observe a lot of their behaviour directly.’

Their results suggest that the success of snakes is down to a little-understood phenomenon known as a ‘macroevolutionary singularity’.

Abominable mysteries

A macroevolutionary singularity isn’t, as the name might suggest, some kind of evolution black hole. Instead it’s a sudden, unpredictable shift in the rate of evolution, thought to be caused by a variety of smaller changes that have built up over time.

These singularities are rare but are known from other groups. Charles Darwin described the sudden appearance and diversification of flowering plants in the fossil record as an ‘abominable mystery’, one which continues to vex scientists today.

Rather than the evolution of one particular trait causing a burst of evolution, it seems likely that it’s a complex combination of different factors, with the exact causes remaining unknown.

However it began, the researchers found that the singularity for snakes seems to start when they gained long legless bodies, flexible skulls, and the ability to detect airborne chemicals.

This allowed them to start specialising to different prey which gave them an advantage over their lizard competitors.

‘One of our key results is that snakes underwent a profound shift in feeding ecology that completely separates them from other reptiles,’ Daniel says. ‘If there is an animal that can be eaten, it’s likely that some snake, somewhere, has evolved the ability to eat it.’

While the evolution of new species shows no signs of slowing down, some snakes may soon face challenges as a result of climate change.

‘Predicting the future is always difficult,' Marc says. 'While it might be assumed that rising global temperatures will allow snakes to do better, what might benefit some snakes will cause problems for others.’

‘Rising temperatures appear to be making some snakes more vulnerable to fungal diseases, while their ability to adapt is being hampered by habitat fragmentation and urbanisation.'

'If these threats lead to an increasing number of extinctions, then the radiation of snakes might be pruned. Nevertheless, for those that remain rapid evolution could be key.’

The team hope future research, examining how certain traits have changed across even larger groups like the vertebrates, might provide a deeper insight into how singularities have shaped the course of evolution.