SECTION D.—ZOOLOGY. 
THE SPECIES PROBLEM 
ADDRESS BY 
PROF. F. BALFOUR-BROWNE, M.A., F.R.S.E., F.Z.S., 
F.R.E.S., P.R.M.S. 
PRESIDENT OF THE SECTION. 
A PREDECESSOR in this Chair called the attention of the Section to the fact 
that Alfred Russell Wallace, in referring to ‘ the curious correspondence 
both in mind and in environment’ by which Darwin and he reached the 
theory of Natural Selection, accounted for it in the first place by the fact 
that both Darwin and he commenced by collecting beetles and thus 
acquired ‘ that intense interest in the mere variety of living things which 
led them to speculate upon the “‘ why”’ and the “ how”? of this over- 
whelming and at first sight purposeless wealth of specific forms among 
the very humblest forms of life.’ 
It is, therefore, with excellent backing that I confess that my main 
interest as a naturalist has always been in this same Order of insects but, 
whereas in the case of these two great men, the study led them to the 
origin of species by means of Natural Selection, I come here hoping that 
absolute faith in that theory is no longer the only hall-mark of a balanced 
mind, because a long experience of the habits and structure of water- 
beetles has led me slowly but surely to the belief that Natural Selection 
plays a much smaller part in the origin of species than has been claimed 
for it. 
I propose to deal mainly with two groups of water-beetles to which 
most of my time has been given, the Carnivorous group or Hydradephaga, 
and the so-called Vegetarian group, the Hydrophilide. From the fact 
that they inhabit water other than salt water, they occupy isolated areas, 
and these can be roughly grouped as ponds, lakes and rivers, and the 
beetles occupying any one pond, lake or river may be described as a 
community. An intensive study of any such habitat produces a list of 
Species forming the community in that particular habitat, and I have 
Spent hours working out the percentages of occurrence of the species in 
1 W. T. Calman, The Taxonomic Outlook in Zoology, Bristol, 1930. 
