IV. SPECIES
In folklore the animals and plants had clear-cut
natures, including moral
characterizations such as we
find in Aesop and in the Oriental and African
fables.
The ancients believed that some types regularly meta-
morphose into each other, for example,
cuckoo hawk
and hoopoe interchange, and wheat can become darnel.
By
this they meant a change of identity, not an ambi-
guity between these types, nor a seasonal change (as
stoat to
ermine).
Plato was the first to apply a philosophical technique
to the conception of
animal types. According to his
theory of Forms, we identify natural
qualities by com-
paring them with ideal
qualities which may not appear
exactly in nature but are known directly to
the mind.
The animal type is an aggregate of characters which
approximate to ideal Forms. The Forms therefore are
an absolute reference
point.
Aristotle inverts this analysis, by taking the animal
type as the exact
object of knowledge, while its char-
acters
vary in precision. Some characters are essential,
some not (for instance,
the eye may be essential, and
an eye must have a color, but its actual
color is ines-
sential and imprecise). The
animal type, namely its
species, is a unified pattern of essential
characters and
functions. It is identical in all members of the
species.
The variations between individuals are due to their
material
makeup, not to their form.
There have been so many conceptions of species in
modern times that it is
perhaps useful to say what
Aristotle's conception is not. It is not a
statistical aver-
age, not a population, not an
approximation, not an
arbitrarily selected type-specimen. On the other
hand,
it is not a form imposed by God. It is a type-pattern
that
exists in nature as an objective datum: it is there
to be detected within
individuals. It differs from any
one individual as absolutely as the
mathematical circle
differs from a drawing of a circle. It is this species-
pattern that Aristotle believes
to be eternally repro-
duced in nature, for
that is the nearest that sublunary
beings can get to the eternal cyclic
movement of the
stars. The fact that it may never be exactly
reproduced
does not affect his point, which is that nature tends
to
reproduce it.
This conception could easily become a belief in fixed
species, but Aristotle
did not consider that point; there
was in fact nothing in his biology that
was incompatible
with an evolutionary theory, had the question ever
arisen. He accepted reports of new species resulting
from miscegenation (he
quotes dog and fox, dog and
wolf, several fishes and birds). He makes only
the pro-
viso that interbreeding is limited to
animals that are
alike in species, size, and length of gestation, and
that
in any case there could not be indefinite production
of new
species, because that would defeat nature's
teleology (meaning that there
would be no goals, for
the goal is the reproduction of the parent's form).
He
emphasizes that the ladder of nature is continuous, and
that many
types overlap the borders of classifications.
Moreover his theory of
reproduction is aimed at ex-
plaining how the
father's form is transmitted and how
the family likeness may come to be
disturbed: the
precise goal is that the animal should “beget
another
like itself,” and its specific form is something
wider
that is only latent in it. There is a contradiction in
his
doctrine here: for he says theoretically that species
is the object of
science while individual differences are
due to matter and are unknowable,
but in practice he
brings to scientific account many characters that
are
below specific level—not only family likeness but ines-
sential attributes such as coloration
and voice. Just
occasionally he suggests that individuals differ not only
in matter but in form too, since the materials that
individualize them could be stated generally; but he
does not follow this
up. (It was followed up by some
medieval scholastics, who thereby removed
this diffi-
culty from his theory of
individuation.)
Aristotle therefore could have accommodated an
evolutionary theory of
species; but he had no need of
it. He had no paleontology, no obsolete
species to
consider; similarity of species could be covered by his
theory; and believing that the world had no beginning,
he had no problem of
the origins of species. By the
third century A.D. some Stoic and
Neo-Platonist theo-
logians had developed
the idea that forms and species
are thoughts in the mind of God. It was
this idea, rather
than Aristotle's theory, that led later scientists
like
Linnaeus to posit the fixity of species.
