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On The Generation Of Animals   

place in the uterus; for he says that if the uterus is hot or cold
what enters it becomes male or female, the cause of the heat or cold
being the flow of the catamenia, according as it is colder or
hotter, more 'antique' or more 'recent'. Democritus of Abdera also
says that the differentiation of sex takes place within the mother;
that however it is not because of heat and cold that one embryo
becomes female and another male, but that it depends on the question
which parent it is whose semen prevails,- not the whole of the
semen, but that which has come from the part by which male and
female differ from one another. This is a better theory, for certainly
Empedocles has made a rather light-hearted assumption in thinking that
the difference between them is due only to cold and heat, when he
saw that there was a great difference in the whole of the sexual
parts, the difference in fact between the male pudenda and the uterus.
For suppose two animals already moulded in embryo, the one having
all the parts of the female, the other those of the male; suppose them
then to be put into the uterus as into an oven, the former when the
oven is hot, the latter when it is cold; then on the view of
Empedocles that which has no uterus will be female and that which
has will be male. But this is impossible. Thus the theory of
Democritus would be the better of the two, at least as far as this
goes, for he seeks for the origin of this difference and tries to
set it forth; whether he does so well or not is another question.

Again, if heat and cold were the cause of the difference of the
parts, this ought to have been stated by those who maintain the view
of Empedocles; for to explain the origin of male and female is
practically the same thing as to explain this, which is the manifest
difference between them. And it is no small matter, starting from
temperature as a principle, to collect the cause of the origin of
these parts, as if it were a necessary consequence for this part which
they call the uterus to be formed in the embryo under the influence of
cold but not under that of heat. The same applies also to the parts
which serve for intercourse, since these also differ in the way stated

Moreover male and female twins are often found together in the
same part of the uterus; this we have observed sufficiently by
dissection in all the vivipara, both land animals and fish. Now if
Empedocles had not seen this it was only natural for him to fall
into error in assigning this cause of his; but if he had seen it it is
strange that he should still think the heat or cold of the uterus to
be the cause, since on his theory both these twins would have become
either male or female, but as it is we do not see this to be the fact.

Again he says that the parts of the embryo are 'sundered', some
being in the male and some in the female parent, which is why they
desire intercourse with one another. If so it is necessary that the
sexual parts like the rest should be separated from one another,
already existing as masses of a certain size, and that they should
come into being in the embryo on account of uniting with one
another, not on account of cooling or heating of the semen. But
perhaps it would take too long to discuss thoroughly such a cause as
this which is stated by Empedocles, for its whole character seems to
be fanciful. If, however, the facts about semen are such as we have
actually stated, if it does not come from the whole of the body of the
male parent and if the secretion of the male does not give any
material at all to the embryo, then we must make a stand against
both Empedocles and Democritus and any one else who argues on the same
lines. For then it is not possible that the body of the embryo
should exist 'sundered', part in the female parent and part in the
male, as Empedocles says in the words: 'But the nature of the limbs
hath been sundered, part in the man's...'; nor yet that a whole embryo
is drawn off from each parent and the combination of the two becomes

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