ation of morphological facts and
its relation to the current morphology of his time.

The sketch of his theory, written in 1842,[352] shows a very significant
division into two parts--the first dealing with the positive facts of
variability and the theory of natural selection, the second with the
general evidence for evolution. It is in the second part that the
paragraphs on morphological matters occur. In paragraph 7, on affinities
and classification, Darwin points out that on the theory of evolution
homological relationship would be real relationship, and the natural
system would really be genealogical. In the next paragraph he notes that
evolution would account for the unity of type in the great classes, for
the metamorphosis of organs, and for the close resemblance which early
embryos show to one another. It is of special interest to note that he
definitely rejects the Meckel-Serres theory of recapitulation. "It is
not true," he writes, "that one passes through the form of a lower
group, though no doubt fish more nearly related to foetal state" (p.
42). The greater divergence which adults show seems to him to be due to
the fact that selection acts more on the later than on the embryonic
stages. He realises very clearly how illuminative the theory of
evolution is when applied to the puzzling facts of embryonic
development. "The less differences of foetus--this has obvious meaning
on this view: otherwise how strange that a horse, a man, a bat should at
one time of life have arteries, running in a manner which is only
intelligibly useful in a fish! The natural system being on theory
genealogical, we can at once see why foetus, retaining traces of the
ancestral form, is of the highest value in classification" (p. 45).

Abortive organs, too, gain significance on the evolutionary hypothesis.
"The affinity of different groups, the unity of types of structure, the
representative forms through which foetus passes, the metamorphosis of
organs, the abortion of others, cease to be metaphorical expressions and
become intelligible facts" (p. 50).

In general, organisms can be understood only if we take into account the
cardinal fact that they are historical beings. "We must look at every
complicated mechanism and instinct as the summary of a long history of
useful contrivances much like a work of art" (p. 51).[353]

Already in 1842 Darwin had seized upon the main principles of
evolutionary morphology: the indications then give