The point which most concerns us is in how far biological data can be
applied to the sex problem in society. Systematic dissections or
breeding experiments upon human beings, thought out in advance and under
control in a laboratory, are subject to obvious limitations. Surgical
operations, where careful data are kept, often answer the same purpose
as concerns some details; but these alone would give us a fragmentary
record of how a fertilized egg becomes a conscious human being of one
sex or the other. The practice of medicine often throws light on
important points. Observation of abnormal cases plays its part in adding
to our knowledge. Carefully compiled records of what does occur in
inheritance, while lacking many of the checks of planned and controlled
experiments, to some extent take the place of the systematic breeding
possible with animals. At best, however, the limitations in
experimentation with human subjects would give us a rather disconnected
record were it not for the data of experimental biology.

How may such biological material be safely used? Indiscriminately
employed, it is worse than useless--it can be confusing or actually
misleading. It is probably never safe to say, or even to infer directly,
that because of this or that animal structure or behaviour we should do
thus and so in human society. On this point sociology--especially the
sociology of sex--must frankly admit its mistakes and break with much of
its cherished past.

The social problem of sex consists of fitting the best possible
institutions on to the biological foundation _as we find it in the human
species_. Hence all our reasoning about which institution or custom is
preferable must refer directly to the human bodies which compose
society. We can use laboratory evidence about the bodies of other
animals to help us in understanding the physical structure and functions