602 
NATURE 
[May 5, 1923 

Selection and Segregation. 
In view of recent discussions in the columns of 
Nature, the following remarks may be of interest. 
Charles Darwin did not explore for himself the vast 
resources of the new territory which he discovered, 
nor did he traverse all the passages leading to it. 
He “‘allured to brighter worlds and led the way.”’ 
In doing so it is possible that he did not arrive at 
the point of disentangling the qualitative from the 
quantitative implications of selection. It will be 
remembered that his theory was followed by long 
discussions on ‘‘ What is a species ? ”’ 
Natural selection is mainly qualitative, while 
specific differences are essentially quantitative. If 
Darwin can be said to have missed this distinction it 
was because he could not anticipate all the objec- 
tions that might be brought to bear upon his mar- 
vellously fruitful concept. Moreover, quality and 
character often appear without any obvious separa- 
tion, and in all cases the mind has to be addressed to 
the task of discrimination. 
It is the province of Mendelism or genetics to deal 
with the analysis of unit characters and to exploit 
favoured individuals. Natural selection is concerned 
with the combination of characters, internal as well 
as external, and with the preservation of favoured 
races. Combination of characters gives quality to a 
genus ; segregation of characters imparts novelty to 
a species. Mendelism and Darwinism clearly belong 
to different categories ; though of course they meet 
on the common stamping-ground of heredity. 
Natural selection is the directive force which con- 
trols the motive impulse of evolution and holds it 
within bounds. It thus becomes to our view the 
guardian of mutations, the custodian of change ; that 
is to say, it provides an automatic control over the 
fitful mutations of the organism. The four pillars of 
organic evolution—struggle, survival, mutation, and 
adaptation—are properly orientated by natural selec- 
tion. This operates in certain directions under certain 
conditions of climate and contact ; 
events which assigns an organism to its place in 
Nature. Nevertheless, the simple thesis had not been 
excogitated before it was expounded by Darwin. It 
was a permanent gain to knowledge which can never 
be repeated, like the discovery of the circulation of 
the blood by Harvey and the biogenesis of reproduc- 
tion by Redi. 
Darwin gave us a theory of qualitative evolution 
by the natural selection of spontaneous variations in 
the open. Survival for an hour or for an eon implies 
unconscious selection for the time being. On the 
other hand, Mendel gave us a quantitative law of 
alternate inheritance of contrasting characters under 
culture. A single example, expressive of many, may 
serve to bring the distinction between intrinsic 
qualities and gross realities into crude relief. 
Leaf-mimicry is one manifestation of interrelation 
of plants and animals, of which floral imitation and 
stick and twig shapes are others. It is a quality so 
intangible that it may be called into question even 
when most obtrusive. Individual observations are 
therefore of little moment until confirmed. The leaf 
butterfly (Kallima) and the leaf insect (Phyllium) 
resemble a leaf in different senses—the former ver- 
tically, the latter horizontally—the recognition of the 
resemblance in these classic examples being old- 
established. Some years ago (‘‘ Spolia Zeylanica,”’ 
II, 1904) it was my privilege to bring to scientific 
notice for the first time the behaviour of a leaf fish 
(Platax) in Ceylon. Similar observations on a species 
of, Platax in the Philippines have since been recorded 
by Dr. Th. Mortensen of Copenhagen. (Vidensk. 
NO. 2792, VOL. 111 | 
it is the chain of | 

Medd. fra Dansk naturhist. Foren., Bd. 69, 1917, 
Pp. 63.) 
Admitting the existence of leaf-mimicry in diverse 
planes and orders, we can only begin to explain it 
on the basis of natural selection, the leaf shape being 
desirable and attainable when other contributory 
factors are equal. * ARTHUR WILLEY. 
Department of Zoology, 
McGill University, 
Montreal, April 1. 

Distribution of Megalithic Monuments. 
In Nature of March 31, p. 442, reference is. made 
to Mr. W. J. Perry’s speculations upon the builders 
of megalithic monuments. Perhaps you will be good 
enough to find room for some criticisms. There 
is a real danger that the scientific study of archezo- 
logy may be overwhelmed by the tide of theorising 
which is now flowing so strongly in this country. 
Mr. Perry believes that the builders of megalithic 
monuments chose to settle in those regions which 
furnished natural supplies of what the note in NATURE 
terms ‘‘ precious metals and other valuables.’”’ If 
so, then why did so many of them settle in the Cots- 
wolds, where natural flint is almost non-existent, 
and where no metals occur? In this region—in the 
counties of Gloucestershire and Oxfordshire—there 
are fifty-six Long Barrows, which Mr. Perry rightly 
includes within the class of megalithic monuments. 
Why are there more than twice as many Long 
Barrows in Gloucestershire alone as in all the other 
flint-producing counties of East and South-east 
England ?—The East Riding of Yorks, Lincolnshire 
(none), Norfolk (none), Cambridgeshire (none), Essex 
(none), Herts. (one), Bucks. (none), Beds. (two), 
Oxfordshire (none in Chilterns), Surrey (none), 
Sussex and Kent (perhaps a dozen at most between 
the two). If it was flint that determined their 
settlement-areas, there is more to be found in any 
single parish of any one of these counties than occurs 
naturally in the whole of Gloucestershire! Why, 
further, is it that there is not a single Long Barrow 
within forty miles of Grimes Graves, the great 
Neolithic flint-mining district of East Anglia, and 
no megalithic monuments within a hundred miles ? 
But the greatest difficulty is in Mr. Perry’s sugges- 
tion that the builders of megaliths travelled in search 
of metals. There is no evidence that the builders of 
British megaliths knew of or made any use of metals. 
Not a single fragment of metal has ever been found 
in a megalithic burial chamber in England, Wales, 
or Scotland. Accordingly, the opinion of archzo- 
logists for half a century has been that all megalithic 
burial-chambers (including those in Long Barrows) 
are neolithic ; and there is no evidence of any sort 
to suggest that this opinion is erroneous, much less 
to prove it wrong. 
Some controlling factors in the distribution of 
Long Barrows over a part of England and Wales 
were suggested in Ordnance Survey Professional 
Paper No. 6. The facts upon which my conclusions 
were based were presented fully, both in tabular form 
and upon a map (O.S. quarter-inch, Sheet 8). For this 
region the facts—about a quarter of them new to 
science —are not available elsewhere. When the 
survey of England and Wales is complete, it will be 
time to draw conclusions about the country as a 
whole. Until then, those interested would be 
serving science better by assisting in the collection 
of facts than by indulging in premature speculation. 
O. G. S. CRAWFORD. 
Ordnance Survey Office, Southampton, 
April 14. 
i462. 
