When danger threatens many lizards can detach their tails, leaving them behind as decoys in the hope that the predator will attack it rather than the lizard itself. But the tail doesn’t just lie there as bait. For half an hour after they’ve been severed, the disembodied tails perform a complex dance, flipping, lunging and jumping up to an inch in the air. These acrobatics serve to distract the predator even further.
For the first time, Timothy Higham and Anthony Russell have studied the movements of severed gecko tails to understand how they can move in such complex ways without any input from the animal’s brain. They anaesthetised four leopard geckos and implanted electrodes into their tails. Once the animals awoke, a small pinch in the right place was enough to prompt them to jettison their tails and scuttle for cover. As the tails started convulsing, Higham and Russell filmed them with high-speed cameras.
Their tips rapidly swung back and forth but between these rhythmic flexes, they behaved more erratically. They flipped by pushing the tip against the floor to launch the whole organ into the air and they lunged by doing the same, but horizontally.
These conspicuous movements increase the odds that an attacking predator will go for the tail instead of the lizard. But it’s actually in the lizard’s interests for both its body and its tail to escape being eaten – geckos and other lizards store valuable reserves of fat in their tails, and these are too valuable to leave to the jaws of another animal. As such, Higham and Russell think that the arrhythmic jumps and flips make the tail more unpredictable and harder to catch. They also increase the odds that the tail will flip to safety, say in a nook or crevice. The lizard can then return later to chow down on its ex-body part.
Classical ballet is one of the more conservative of art forms. Dancers express emotion and character through the same vocabulary of postures that was originally set in 1760, and often with entire choreographies that have been handed down for centuries.
But even amid this rigorous cascade of tradition, there is room for change. Over the years, successive generations of ballet dancers have subtly tinkered with positions that are ostensibly fixed and limited by the physical constraints of a dancer’s body. The only changes ought to be a result of the dancers’ varying abilities. But that’s not the case – over the last 60 years, the position of a dancer’s has become increasingly vertical, with the moving leg in particular being lifted ever higher.
Elena Daprati from the University of Rome thinks that these tweaks have been driven by social pressures from audiences. When she reduced pictures of dancers to stick-figure drawings, she found that even people who have never seen a ballet prefer the postures of modern dancers to those of dancers 60 years ago. The results suggest that art can change very gradually because of constant interactions between performers and their audiences.
Almost more importantly, they show that the usually unquantifiable world of artistic expression can be studied with a scientific lens. In this case, the formal nature of classical ballet gave Daprati a rare opportunity to do so. Body postures could be objectively analysed, movements are standardised enough to allow for easy comparisons, and most of all, performances have been carefully archived for decades. That provided Daprati’s group with more than enough raw material for studying the evolution of ballet postures over time.