From Andrew Stiller
The finding that just three of the many citrus varieties gave rise to all the others
(18 August, p 12)
is fascinating, but it’s debatable whether these three are the only species.
At present, human intervention keeps all citrus varieties reproductively
isolated from each other, and reinforces their distinctive phenotypes. The
original three differ not a bit from the others in this respect, so why should
they alone be considered species?
This raises the larger issue of why cultivated varieties of organisms should
not be considered species. If two organisms have distinct phenotypes and are
reproductively isolated, it should not in theory make any difference how they
came to be so. They ought to be considered separate species.
The distinction between natural and cultivated organisms, while convenient,
is hugely arbitrary, and has tended to distort discussion of such issues as the
net effect of human acivity on global biodiversity.
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