Image: Dorian Kartalovski
Different animals are associated with distinct abilities that other species do not possess. Birds can fly and humans cannot because their body types have developed to fill different niches. A spider’s ability to climb a vertical wall goes unquestioned, but the fictional Spider-Man’s ability to do so makes him a superhero. So why is it that with our superior technology, we cannot simply use science to adapt our human bodies to possess the abilities of other species. Why can we not start making superpowers a reality?
The study of allometry seeks to understand the relationship between the size of an animal’s body, its shape, its abilities and behaviour. Research recently published by Dr David Labonte and his colleagues at Cambridge University have explored how adhesive forces differ for living creatures over a huge range of sizes. Simply put, certain animals have sticky footpads which allow them to stick to and move about on walls and ceilings. The team were investigating how these animals cope with increasing body size.
Instinctively, one might think that if a spider can stick to a wall with tiny points of contact, then a larger animal should also, so long as the size of the contact points was scaled up proportionally. However, due to the surface area to volume ratio, this is not the case. Surface area is the area covered by an animal’s body. The volume is the space occupied by it. The ratio is the relationship between the two quantities. The surface area to volume ratio is used a lot by biologists to understand how different animal bodies work, and is crucial to the field of allometry. As an example: a spider is a really small animal, but it is almost all surface, and very little volume, so despite being tiny, its surface area to volume ratio is enormous. A human on the other hand, occupies quite a lot of space, with relatively less surface area, so its surface area to volume ratio is quite low.
This is why spiders can climb so easily. They are so delicate that they only need a tiny proportion of their body’s surface area in contact with a wall, about one per cent, and they will happily stick to it with all of their bulk supported. A gecko, the largest known animal to climb using sticky footpads, needs about four per cent of its body’s surface in contact with the wall in order to stay put. A human on the other hand, would need a massive 40 per cent of their body’s surface to be covered in sticky stuff. So in order to climb about like a spider, a real life Spider-Man would need to have feet over a metre long. Which just is not quite as cool as super-adhesive fingertips.