398 r SECTIONAL TRANSACTIONS.—D. 
emigration, mainly to N. America. There were about 5,000,000 people in England 
and Wales in 1700, 8,750,000 in 1800, and about 33,000,000 in 1900. It isto the credit 
of Miss Buer to have shown that these increases are due not to an increased birth-rate 
but to an increased survival rate, which she attributes to improved medicine and to 
humanitarian effort. Of children born in London three-quarters died before reaching 
the age of five in 1730; in 1830 only one-third of those born died before the age of five. 
Since the war emigration. which corresponds to prehistoric migration, has been 
so restricted that relief from this source is minimal; and though the birth-rate is 
falling off, this is due to decreased fertility amongst the prudent and thrifty, not 
amongst the stupid and careless. If this goes on the constitution of our population 
will be radically changed, and our greatness will disappear. The only remedy seems 
to be the spread of the knowledge of the means of birth control, and in the last resort 
compulsory sterilisation. 
Monday, September 28. 
Discussion on Classification with reference to Phylogeny and Convergence. 
(Dr. C. Tate Reean, F.R.S.; Dr. F. A. Batuer, F.R.S.; Dr. W. D. 
Lane, F.R.8.; Dr. J. StepHenson, F.R.S.; Dr. Huan Scort.) 
Dr. F. A. Batuer, F.R.S. 
Classification must be practical, its object being to enable us to name and place 
assemblages so that we can make statements concerning them. Classification must 
be based on verifiable fact, not on inference. If we knew all, could we construct a 
Phylogeny ? If we could, then could we express it in classification ? We do know 
enough to see that we should meet many difficulties. 
Beginning near the base, with apparently homogeneous populations, we know 
from genetic experiment that they are often heterogeneous. The composite nature 
of many fossil populations of a single species has been shown by Trueman and others. 
The species itself comprises many races (Jordanons in the Linneon). Parallel forms 
or isomorphs appearing in allied species, as shown by Vaviloff, may represent identical 
genetic factors. The species then is heterogeneous. Genera also are heterogeneous, 
not because each is composed of distinct species, but because its constituent species 
represent lineages that have passed into it from some pre-existing genus or genera 
(parallelism or convergence). For examples, refer to Bather, Presidential Address 
Geol. Soc., July 1927, and Schindewolf, Palwont. Zeitschr. IX, 122-169, August 1927. 
The difficulty arises in deciding whether to select grades of structure or lines of descent 
as bases of genera. The latter, besides being inferred, are difficult of definition, except 
as (supposed) descendants of a (presumed) single ancestor. To adopt both vertical 
and transverse divisions is to produce an arrangement like a crossword puzzle, in 
which each generic pigeon-hole may contain but one species. While such parallelism 
is common, it is very difficult to find clear evidence for the splitting of one species 
into two, such as may ultimately give rise to two genera. Divergence generally 
affects diverse forms. A generic grade may arise in different places (Metaxytherium), 
or at different times (Gryphea), or both (Balanocrinus). Phylogeny a outrance leads 
to pulverisation of genera; we want rather to return to larger genera, and to make 
more use of the grade concept. A nomenclature and a classification based on 
ascertainable fact will enable us to construct any number of phylogenies according 
to each worker’s interpretation. 
Similar difficulties are met with in the larger groups, and are to be overcome in 
the same way, by greater use of the Grade. 
Though classification must be based on structure, it needs a rational foundation— 
an expression preferable to ‘ natural’ and not a whit more subjective. Seeking the 
causes of structure we find : (a) the material, 7.c. all inherited structures and qualities ; 
(b) the forces that fashion it, 7.e. environment, both outer and inner, this also expressed 
as ‘functional.’ But the hereditary material itself was once fashioned by the 
environment, and so continuously backward. Distinction between the successive 
characters is possible only through paleontology. It is the relative age that confers 
morphological importance and decides what is convergence and what only parallelism. 
a ae 
