Presidential
address by a review of the "old judgments" which he had given in the
course of his first address in 1862. The address was entitled
"Palaeontology and Evolution," and the most important part of it was a
complete withdrawal of the fears he had expressed that geology would
not supply definite evidence of the transformation of species.
Important discoveries had come thick and fast; and, at least in the
case of the higher vertebrates, he declared that, however one might
"sift and criticise them," they left a clear balance in favour of the
doctrine of the evolution of living forms one from another. But, with
his usual critical spirit, examining arguments that bore against a
conclusion for which he hoped almost more stringently than arguments
apparently favourable to what he expected to be true, Huxley made an
important distinction, the value of which becomes more and more
apparent as time goes on. In the first flush of enthusiasm for
Darwinism, zooelogists and palaeontologists allowed their zeal to outrun
discretion in the formation of family trees. They examined large
series of living or extinct creatures, and so soon as they found
gradations of structure present, they arranged their specimens in a
linear series, from the simplest to the most complex, and declared
that the arrangement was a representation of the family tree. The fact
that the line of descent apparently could have followed along the
direction they suggested they were inclined to take as evidence that
it had so followed. Huxley made the most careful distinction between
what he called intermediate types and types with a right to be placed
in linear order,

Every fossil which takes an intermediate place between forms of
life already known may be said, so far as it is intermediate, to
be evidence in favour of evolution, inasmuch as it shews a
possible road by which evolution may have taken place. But the
mere discovery of such a form does not, in itself, prove that
evolution took place by and through it, nor does it constitute
more than a presumptive evidence in favour of evolution in
general. The fact that _Anoplotheridae_ are intermediate between
pigs and ruminants does not tell us whether the ruminants have
come from the pigs or the pigs from the ruminants, or both from
_Anoplotheridae_, or whether pigs, ruminants, and _Anoplotheridae_;
alike may not have diverged from some common stock.