A paper published in PNAS (Proceedings of the National Academy of Sciences) by Labonte et al. may threaten the existence of Spiderman as we know him.
The paper, which focuses on allometry – the study of biological scaling, finds that there is an upper body weight limit to adhesive climbing. The researchers studied 225 different species and found that the percentage of an animal’s body that needs to be covered in adhesives increases as body size increases.
In fact, the paper states that geckos are the heaviest creatures that are able to climb walls in this way. Spiders, despite being very different to geckos in many ways, have remarkably similar footpads and are small enough to climb adhesively without any problems. This is a clear demonstration of convergent evolution: the process by which unrelated species independently evolve similar features, as a result of having to respond to the same challenges.
However, if Spiderman wanted to live up to his name then he would need to cover at least 40% of his body with adhesive pads.
“If a human, for example, wanted to walk up a wall the way a gecko does, we’d need impractically large sticky feet – our shoes would need to be a European size 145 or a US size 114,” says Walter Federle, a senior author from Cambridge’s Department of Zoology. Hardly convenient for a life of undercover crime fighting.
Although many larger animals have had to develop alternative climbing methods, such as claws and toes, in order to face the same obstacles as their smaller counterparts, there is another evolutionary solution. Some species of frogs, despite being heavier than geckos, have adapted to compensate for their weight by developing pads that are stickier rather than larger. Perhaps there is a shred of hope for Spiderman after all.
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