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.

A familiar instance will make the point at issue plain.  Everyone knows that in many respects, in the structure of the skeleton, and the curve of the backbone, and in the development of the brain, the man-like monkeys, the gorilla and its allies, are intermediate between man and the lower monkeys.  In the early days of evolution it was assumed frequently that the gorilla, etc., were therefore to be regarded as ancestors of man, and they appear as such in more than one well-known treatise on evolutionary biology.  We now know that it is exceedingly probable that the gorilla and its allies, although truly intermediate types, and truly shewing a possible path of evolution from the brute to man, are not the actual ancestors of man, but cousins, descendants like man from some more or less remote common ancestor.  And the tendency of recent advances in knowledge is more and more to throw stress on the value of Huxley’s distinction, and to minimise confusion between “intermediate” and truly ancestral types.

CHAPTER VI

HUXLEY AND DARWIN