Alan Turing is well known for his work on cryptography and computer science. However, Thomas Woolley from St John’s College, Oxford has come to Café Sci and The Vat & Fiddle to talk about his work in biological pattern forming, including how the fish got its spots.
Turing started looking at biological pattern forming in 1952 and he was interested in diffusion. Now diffusion, for example the way that ink spreads in water, is a random motion that wipes out patterns. While diffusion can sometimes create patterns, such as the French flag pattern, this is actually a pattern forming from a source – a pattern from a pattern.
Similarly in chicken embryos, digit development occurs in polarising regions with the help of the so-called “Sonic the Hedgehog” protein. This protein diffuses over the region and digits form. Turing wanted to know what happens without a source. For example how does an embryo become a baby?
So, can we have two chemicals that defuse? ie something that has no pattern and something (diffusion) that wipes out patterns.
In nature, we have patterns such as a leopard’s spots and the markings on a giraffe. If we discount Rudyard Kipling, what can these patterns tell us? Well, they can tell us about developmental constraints. For example, tapered domains where patterns simplify. In a lot of the big cats, you can see spots on the body that then become stripes on the tail (although there are counter-examples to this such as the ring-tailed lemur which has no spots but stripes on the tail)
We see some slightly strange results with the tapir where the young have stripes but the adults don’t. There are also some really interesting patterns when it comes to both the Valley Goat and the Galloway Cow.
Turing patterns do have their problems though. While having random arrangements is brilliant when it comes to things like spots, there are times when you want specific results. For example, in humans, you want to have two arms. However, it is still possible to get over this robustness problem.
Can we actually pinpoint Turning patterns in nature? Not yet. Although three years ago a group in Spain did manage to prove that you could manipulate the number of fingers in a mouse up to fourteen.
So, how did the fish get its spots? Well, we don’t actually know but it could have been due to Turing patterns. To create your own Turing patterns, download a simulator here.