Posts tagged morphogenesis

Sonic hedgehog is one of three proteins in the mammalian signaling pathway family called hedgehog, the others being desert hedgehog (DHH) and Indian hedgehog (IHH). SHH is the best studied ligand of the hedgehog signaling pathway. It plays a key role in regulating vertebrate organogenesis, such as in the growth of digits on limbs and organization of the brain. Sonic hedgehog is the best established example of a morphogen as defined by Lewis Wolpert’s French flag model—a molecule that diffuses to form a concentration gradient and has different effects on the cells of the developing embryo depending on its concentration.

via https://en.wikipedia.org/wiki/Sonic_hedgehog#Controversy_surrounding_name

If you want to get a rough grasp of how the leopard might get its spots, then building a CA model (or something similar) can be very illuminating. It will not tell you whether that’s actually how it works. This is an important example, because there is a classic theory of biological pattern formation, or morphogenesis, first formulated by Turing in the 1950s, which lends itself very easily to modeling in CAs, and with a little fine-tuning produces things which look like animal coats, butterfly wings, etc., etc. The problem is that there is absolutely no reason to think that’s how those patterns actually form; no one has identified even a single pair of Turing morphogens, despite decades of searching. [See “Update, 4 March 2012” below.] Indeed, the more the biologists unravel the actual mechanisms of morphogenesis, the more complicated and inelegant (but reliable) it looks. If, however, you think you have explained why leopards are spotted after coming up with a toy model that produces spots, it will not occur to you to ask why leopards have spots but polar bears do not, which is to say that you will simply be blind to the whole problem of biological adaptation.

http://vserver1.cscs.lsa.umich.edu/~crshalizi/reviews/wolfram/