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Logic II 43d

we can most certainly rely as being natural. No
harm will be done if, in those cases, we define the
natural classification as the genealogical classification;
or, at least, that we make the genealogical
character one of the essential characters of a
natural classification. It cannot be more; because
if we had before us ranged in ancestral order all the intermediate forms
through which the human stock has passed in
developing from non-man into man, it is plain
that other considerations would be necessary in
determining (if it admitted of determination)
at what point in the series the forms began to merit
the name of human. The sciences are, in part, produced
each from others. Thus, spectroscopic
astronomy has for its parents, astronomy, chemistry,
and optics. But this is not the whole genesis nor
the principal part of the genesis of any broad and