(aminopeptidase Q), which likely responds to chemical signals from
nearby cells (Kaelin et al., 2012). Apparently, then, tigers can change
Other factors can affect overall pigmentation: yet another way
to change one’s spots or stripes. Black panthers are really leopards
in disguise. Melanocytes active over the entire surface eclipse the
underlying rosette pattern. Using infrared light, however, one
can still detect the spots (Figure 11) (Hedges et al., 2015). Here,
we notably encounter a vestige of the past, which helps to document the change that occurred. One can also lose an “essential”
pattern through loss of relevant pigments, as in the spotless cheetah (Figure 12).
Of course, it is easy to imagine how morphogens or developmental
factors may be genetically based. Proteins that help regulate cell processes will be encoded by genes. And those genes may mutate. Further,
a mutational change in the germ line may be passed on to the next generation. When that happens, a pattern variant (even if rare) may well be
shared by different offspring of the same parent(s), as in the cases noted
above. Recently, the tabby pattern factor in felids (mentioned above)
has been mapped to the gene Taqpep. A second gene contributes to
the coloration by responding to the underlying Turing patterns (Kaelin
et al., 2012). In another case, in mice the Mitf gene is responsible for
development of melanocytes, but it can be suppressed by Alx3. Both
are implicated in the white stripes of chipmunks (Mallarino et al.,
2016; Yong, 2016).
Once such mutations emerge, their developmental consequences can cascade through succeeding generations, changing the lineage: hence, evolution. That would surely explain the similarities and
differences in striping among the various zebra types in Africa
(Figure 8), along with the now extinct quagga (Figure 13): they all
reflect pattern changes from some common ancestor (Leonard,
2005; Larison, 2012). Ultimately, the “essential” features of a species –
epitomized by the tiger’s stripes – are open to developmental change,
possibly for the long term.
Essentialism & the Irony of Change
What is a species’ “essence” Ironically, while the image of a tiger’s
essence seems to be its unchangeable stripes, the imagined essence
of a chameleon is quite the opposite: namely, its ability to change
its color. Other organisms, too, change their color or appearance
in short-term physiological or behavioral responses: squid and cuttlefish, flounders, cichlids, wrasse, anolis lizards, and the golden
tortoise beetle, among others. Indeed, responses to changes in the
environment seem commonplace. Some of those changes may be
short term, some long term. Behavior, development, cellular processes, ecology, and inheritance all interact. So that raises the question again of why we might expect to find immutable essences
among living things.
Yes, a tiger can change its stripes. Zebras, too. And zebrafish.
And cats and mice and chipmunks. And human hands, in a sense.
Likewise, leopards can change their spots. Along with cheetahs.
The ultimate question may be instead: Can human assumptions
about essentialism also change, through learning?
Note: All images are available electronically at http://sacredbovines.
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Figure 13. One of the last quaggas in 1870, its coloration
reflecting its divergence from other zebra types (see Figure 8)