248 SECTIONAL ADDRESSES. 
last decade of last century. It was not precisely Darwin's own position, 
but gained its great vogue, especially in this country, largely through 
the writing of Alfred Russel Wallace, and through the germ-plasm theory 
of August Weismann. All characters whatever, as Dr. Scott and Sir 
Ray Lankester said, were regarded as .adaptive or useful in the first 
instance, and as produced by the summation of small variations. The 
origin of these variations was obscure. The fact that such variations 
occurred was sufficiently established, and their occurrence was simply 
taken as a datum on which natural selection could work by picking 
out and establishing the favourable ones. The only characters which 
were not considered adaptive at their first origin were covered by the 
conception of ‘ correlated variation,’ 7.e. structural or functional changes 
necessarily involved by the primary adaptive ones, though not in them- 
selves useful to the organism. Later on the structural changes which 
were at first useful might be so no longer, owing to their supersession 
by other structures or by a change of conditions. They were, however, 
or might be, still inherited, being incorporated in the constitution of 
the organism’s germ-plasm, though superseded, so far as current adapta- 
tion went, by more recently acquired characters, as in the familiar case 
of the embryonic gill-slits of the higher vertebrates. Frequently an 
organ originally acquired for one purpose was diverted to different uses, 
as for instance the anterior fins of fishes, which became, in their modi- 
fied terrestrial descendants, legs, arms, or wings. Thus the actual 
structure of an organism could only be explained by its ancestral history. 
The weak point of this theory of evolution, on the facts then known, 
apart from the obscurity surrounding the origin of variations, was the 
difiiculty of understanding hew the first minimal variations, which were 
supposed to be the foundation of new structures, could, at least in many 
cases, be of life-preserving value— survival value,’ as the phrase goes— 
to the organism, and how they could avoid being ‘ swamped,’ as it was 
supposed would happen, by intercrossing with other unmodified mem- 
bers of the species. Various theories of segregation, geographical or 
physiological, were proposed to get over this difficulty, but it was very 
doubtful if they could be considered as of sufficiently wide application 
for the purpose. Further, the theory required that the actual structural 
differences between species—apart from * correlated variations "—should 
always be adaptive; yet the greater number of naturalists who had a 
wide first-hand acquaintance with species as they exist in the field, and 
with the actual differences between allied species, could not find that 
this was the case. Some people attributed this scepticism to ignorance 
of the functions of particular structures which seemed to be useless, the 
Neo-Darwinians refusing to admit that constant characters might have 
no ‘ function ’ after all, unless they were vestigial or ‘ correlated’ with 
others that had. The field naturalists, however, remained for the most 
part obdurate. One distinguished biologist, referring to the hope that 
all specific characters would ultimately be proved adaptive, added, 
‘Time has been running now and the hope is unfulfilled.’ Ingenious 
persons explained all sorts of peculiar structures and arrangements— 
‘myrmecophily,’ the insectivorous habit of some plants, extra-floral 
nectaries, the long tips of certain tropical leaves, and countless others— 
