Species

292 Species

Each of these has a philosophical analogue or equivalent. Gradism is essential-
ism, phenetics is (quite overtly) based on Wittgensteinian family resemblance, and
cladism is either an Aristotelianism or a nominalism. It is odd that while essential-
ism is considered fallacious in biology and especially in taxonomy, largely due to the
advocacy of Ernst Mayr, it is the received view in philosophy of language. Recent
work, neatly summarized by Susan Gelman,^29 suggests that we are all born essen-
tialists, which therefore raises the question: must we remain essentialists? If biology
is not just the essences of kinds, then of course once we commence our investiga-
tions into biology we need not remain essentialists; but oddly Mayr, who stridently
opposes the idea that species and populations are essentialistically definable, none-
theless adopts a gradist perspective when classifying taxa in addition to genealogical
“ordering.” Let us consider why his “evolutionary systematics” adopts this chimeric
approach.
According to Mayr and Simpson, the genealogical aspect of evolution, which
Darwin called “common descent,” is paramount, but nevertheless, we can overlay
on that evolutionary history further divisions based on the evolutionary “niche” or
“grade” that some branches achieve. For example, there is some similarity of life-
style and body plan that groups crocodiliforms and reptilians together, even though
in cladistic—that is, evolutionary genealogical—terms reptiles and birds are more
closely related, which is to say they share a more recent common ancestor. The
“avian grade” is sufficiently distinct from the “reptile-like” body plans that we can
ignore “propinquity of descent” as a grouping criterion in this case. A similar case is
put for humans: we are sufficiently different from other apes and primates in general
that we must form our own named group. In fact, Julian Huxley once suggested,
half-seriously, that we ought to form a new kingdom, Psychozoa, of cultural animals
with mind and language.^30 This kind of grade/clade hybrid is a paraphyletic group, if
more than one species attains it.
In large part, such claims depend critically on the importance of the factors used
in defining the grade. Perhaps there is a grade of parrots that can act cute and mimic
language—if so, the only thing saving science from making this a grade, and from a
host of similarly arbitrary grades, is the fact that scientists do not think “acting cute
and mimicking language” forms a natural kind, while “feathered flying animals,”
and “mentally endowed language users,” do form two kinds. If they do, though, it is
clear in an evolutionary sense that such grades can be achieved more than once by
different genealogical routes. In other words, feathered birds and talking brainy apes
might evolve more than once. Cuteness is a subjective grade, which depends on the
criteria of the observer. We shall not consider subjective grades as worthwhile kinds
here, as to do so amounts to adopting conventionalism.
The cladistic account is more particularistic in the ontological sense—each branch
of the tree is a singular historical object. What the scientists think is important is not of
any real relevance to the “naturalness” of the groups. What happened to them in their
history is. It may be that one can identify “kinds” such as “warm-blooded”—once

(^29) Gelman 2004.
(^30) Huxley 1957a, 91.