Proof that Spiderman cannot exist. Geckos are the biggest possible wall-climbers
Researchers have established that geckos are the largest animals which can scale smooth, vertical walls. Larger creatures would need incredibly large footpads to achieve the gravity-defying feat – humans would require pads over roughly 40 percent of their body to climb up the wall like ‘our friendly neighbour’ Spiderman.
That Spiderman was only living in comics and movies was given, but now scientists have produced new evidence that would convince even the most sceptical of the fans. The study was published last week in the journal PNAS and shows that in all wall-climbing animals – from mites and spiders up to tree frogs and geckos – the proportion of body surface covered by adhesive footpads increases with body size, limiting how much these animals can actually grow big.
According to Dr David Labonte and collaborators, at Cambridge University, mites have roughly 200 times less body surface dedicated to sticky pads than the much larger geckos. Human-size animals would need about 40% of their body covered in footpads to achieve the same result, making this strategy actually impractical from an evolutionary standpoint.
“As animals increase in size, the amount of body surface area per volume decreases – an ant has a lot of surface area and very little volume, and a blue whale is mostly volume with not much surface area” explains Labonte. The study hence poses serious questions about the feasibility of artificial, bio-inspired human sized adhesives.
The researchers studied over two hundred different climbing animals, spanning from insects to reptiles and even a mammal, and found – quite strikingly – many similarities. “Adhesive pads of climbing animals are a prime example of convergent evolution – where multiple species have independently, through very different evolutionary histories, arrived at the same solution to a problem. When this happens, it’s a clear sign that it must be a very good solution,” Labonte commented.
In evolutionary terms, one could imagine the possibility of stickier rather than larger pads, and this is indeed the case. “Within frogs, we found that they have switched to this second option of making pads stickier rather than bigger. It’s remarkable that we see two different evolutionary solutions to the problem of getting big and sticking to walls,” says co-author of the study Chrystofer Clemente from the University of the Sunshine Coast. “This is a great example of evolutionary constraint and innovation,” he concluded.
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