white stripes along the midline of the back form by switching off pigment production in the band’s melanocytes (Figure 7) (Mallarino
et al., 2016; Yong, 2016).
To change these patterns, all one need do is tweak one of the
variables: the rate of the diffusion, the amount diffused, the initial
timing, the response of the cells to particular concentrations of
the diffusing signals. They can change the complexity, the size,
the direction, or the regularity of coloration patterns (Allen et al.,
2011). For example, if one changes the time when the pattern
begins to form, zebras (from different species) develop different
numbers of stripes, with different widths (Figure 8) (Bard, 1977).
In the same way, human hands can develop more bands, and hence
more digits: polydactyly (Figure 9).
Recent research shows that in domestic cats, a single factor governs the transition between two tabby patterns: “mackerel” (striped)
and “blotched” (Figure 10) (Eizirik et al., 2010). That same factor
also transforms a cheetah into a “king cheetah” – once viewed
as so different that it was construed as a separate species entirely
(Figure 5)! The key element in this case is a transmembrane protein
Figure 9. Our hands are striped. Polydactyly reflects a change
in the underlying Turing pattern, based on timing in
Figure 10. The transition from “mackerel” to “blotched” tabby
cat is governed by one transmembrane protein (potos by
Hirashi and Cassie J., cc2 Wikimedia).
Figure 11. A melanistic leopard (or “black panther”) shows its
spots in infrared imaging (photo courtesy of Laurie Hedges).
Figure 12. A spotless cheetah, like a black panther, shows
pigmentation effects that eclipse underlying patterns (photo by