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of living things
classification of living things contains some elements which still existed in
the 19th century. What the modern zoologist would call vertebrates and
invertebrates, Aristotle called 'animals with blood' and 'animals without
blood' (he was not to know that complex invertebrates do make use of haemoglobin,
but of a different kind from vertebrates). Animals with blood were divided into
live-bearing (humans and mammals), and egg-bearing (birds and fish).
Invertebrates ('animals without blood') are insects, crustacea (divided into
non-shelled – cephalopods – and shelled) and testacea (molluscs). In some
respects, this incomplete classification is better than that of Linnaeus, who
crowded the invertebrata together into two groups, Insecta and Vermes (worms).
Charles Singer, "Nothing is more remarkable than [Aristotle's] efforts to
[exhibit] the relationships of living things as a scala naturae"
Aristotle's History of Animals classified organisms in relation to a
hierarchical "Ladder of Life" (scala naturae), placing them
according to complexity of structure and function so that higher organisms
showed greater vitality and ability to move. Aristotle believed that
intellectual purposes, i.e., final causes, guided all natural processes. Such a
teleological view gave Aristotle cause to justify his observed data as an
expression of formal design. Noting that "no animal has, at the same time,
both tusks and horns," and "a single-hooved animal with two horns I
have never seen," Aristotle suggested that Nature, giving no animal both
horns and tusks, was staving off vanity, and giving creatures faculties only to
such a degree as they are necessary. Noting that ruminants had multiple
stomachs and weak teeth, he supposed the first was to compensate for the
latter, with Nature trying to preserve a type of balance.
a similar fashion, Aristotle believed that creatures were arranged in a graded
scale of perfection rising from plants on up to man, the scala naturae
or Great Chain of Being. His system had eleven grades, arranged according
"to the degree to which they are infected with potentiality",
expressed in their form at birth. The highest animals laid warm and wet
creatures alive, the lowest bore theirs cold, dry, and in thick eggs.
also held that the level of a creature's perfection was reflected in its form,
but not preordained by that form. Ideas like this, and his ideas about souls,
are not regarded as science at all in modern times.
placed emphasis on the type(s) of soul an organism possessed, asserting that
plants possess a vegetative soul, responsible for reproduction and growth,
animals a vegetative and a sensitive soul, responsible for mobility and
sensation, and humans a vegetative, a sensitive, and a rational soul, capable
of thought and reflection.
in contrast to earlier philosophers, but in accordance with the Egyptians,
placed the rational soul in the heart, rather than the brain. Notable is
Aristotle's division of sensation and thought, which generally went against
previous philosophers, with the exception of Alcmaeon.