The fairground freakshows of the past are a testament to our fascination with unusual animals. Given the similarities between most furry, four-legged mammals, it’s not surprising that we often look at the more weird and wonderful members of the animal kingdom and ask questions like “Why does a spider have so many legs?” or “Why are snakes so long?”.
The answers can usually be found in evolution and genetics. More specifically, we need to study how animals have evolved so that the shape and layout of their bodies are formed as they grow from embryos (part of evolutionary developmental biology or “evo-devo”). If we want to know why a snake is so long, we need to start looking at snake embryos.
One group of researchers from the Instituto Gulbenkian de Ciência in Portugal has done just that. They found that one gene in particular plays a key role in shaping the snake’s extra-long body. The researchers were able to prove this by turning on the same gene in mice to produce animals with much longer than normal bodies.
There are basically two ways a vertebrate animal can evolve a long body: by increasing the size of vertebrae (as in a giraffe’s neck) or increasing the number of vertebrae (as in a goose’s neck). This increase can take place in the neck, the trunk or the tail.
In the case of snakes, their extreme length is a product of a longer trunk, as shown by the large number of vertebrae possessing ribs. These continue to grow far beyond what is typical for other reptile embryos thanks to the faster vertebrae formation during development, and their unusual “Hox” genes, which determine which type of vertebrae develop.