But a report in Science back in December (only just arrived in the British Library after supply problems) shows that Alan Turing’s reaction–diffusion process may be involved. This was proposed in 1952, a year before DNA let alone genome biology and for a long time was regarded with suspicion by biologists. But it is very much back in the frame now. Turing’s mechanism was originally devised to explain stripes and spots but if you think about it, digits are stripes: digit, no digit, digit, no digit . . . It has long been known that the hand begins as a one-piece and between the digits cells have to die to create the famous five. Now it seems that hox genes control the expression of sonic hedgehog. In mice, knocking them out causes a progressive increase in digits – 14 being the maximum attained so far. The researchers interpret the extra digits in terms of Turing’s theory: the wavelength of the reaction–diffusion patterns has been changed by the hox genes, resulting in more toes in the same space. There’s lets more to learn about this but new insights into form such as this are coming thick and fast now.
Science, 2012, 338, pp. 1406 and 1476.