324 
oldest starfish of all are neither Cryptozonate nor 
Phanerozonate and have no plates corresponding to 
the marginals of Astropecten at all. 
Lastly, as to the accusation that I belittled Dr. 
Mortensen’s work. I have no wish to depreciate his 
work, but with the exception of the treatise on the 
Crinoids (Comatulidz), which is irrelevant to the point 
at issue, it is not what I regard as embryology at all. 
By that term I understand the attempt to follow 
through the development of the organs of the adult 
from their beginnings in the embryo or larva with a 
view of obtaining light on the ancestry of species. 
Dr. Mortensen’s researches on Echinoderm larve have 
been purely classificatory, and he has done valuable 
work in determining which larval forms belong to 
certain adults. His recent work on Comatulide, it is 
true, is embryological: he has confirmed the results 
of Bury and extended them to cther species ; but he 
dismisses the conclusions of other embryologists 
without sufficient consideration of facts. 
E. W. MacBriveE. 
Imperial College of Science and Technology, 
South Kensington, London, S.W., 
February 2. 


Medical Education. 
I am sorry Prof. Dakin (NATURE, February 3, p. 
151) should think my letter (NATURE, January 
I3, p. 50) merely an attempt to open another dis- 
cussion on evolution. I do not know how I could 
have expressed myself more clearly. Manifestly, a 
knowledge of such things as the anatomy of frogs and 
dog-fish cannot persist in the minds of medical 
students or be useful to them intellectually or pro- 
fessionally unless linked with other studies. They 
can be so linked only through truths about develop- 
ment, variation, heredity, and evolution. But here 
the naturalist is in conflict with the physiologists, 
psychologists, pathologists, and medical men into 
whose hands the students pass and whose opinions, 
abundantly supported by evidence, they always 
adopt. 
It is one thing to demonstrate that evolution has 
occurred, and for this none are better qualified than 
naturalists. But evolution is not disputed by 
medical men, though, owing to the biology they | 
learn, few give it a thought. It is quite another 
thing to demonstrate the method of evolution. Here, 
to say the least, naturalists are not in a position to 
ignore evidence derived from other sciences. For 
example, they have very diverse opinions about 
fluctuations. But did ever a naturalist see a fluctua- 
tion in a living being existing under natural condi- 
tions, other than man (e.g. a sparrow or house-fly, 
the most familiar of all) ? If he did, was he able to 
follow that being throughout its career and test the 
influence of that fluctuation on its life ? 
was he able to note the effect on offspring and 
descendants ? 
fluctuations, natural selection, and the method of 
evolution is derived from human beings, among 
whom alone we are able to observe with that suffi- 
ciency and minuteness which extreme familiarity 
confers. Thus every man (not only Prof. Dakin’s 
superman) knows that powers of resisting the car- 
nivorous bacillus of tuberculosis occur in all shades 
between wide extremes (therefore they are fluctua- 
tions); that they tend to run in families (therefore 
they are inheritable); that the less resistant tend to 
perish and the more resistant to survive (therefore 
there is natural selection) ; that every race is resistant 
n proportion to the length and severity of its suffer- 
NO, 2784, VOL. 111] 
If he did, | 
NATURE 

[Marcu 10, 1923 
ings (therefore natural selection is the antecedent 
of evolution); and that what is true of tuberculosis 
is true also of every lethal and prevalent disease 
(therefore the instances are in thousands and include 
all the world and all humanity—indeed every case in 
which we are able to observe closely). 
Naturalists, unable to observe‘either fluctuations or 
natural selection among plants and lower animals, 
must get their ideas about the method of evolution 
mi 
either from observations on man or else through mere ~ 
guessing. Apparently they prefer not only to guess 
but to claim scientific status for their guesses. After 
all, man is an animal. I do not know why he should 
be thought unworthy of study. 
What does Prof. Dakin mean by “it is highly 
desirable that first-year medicals, raw youths from 
school, should make their first acquaintance with the 
animal world through less expensive material than 
human bodies’’ ? Expensive in what—money or time ? 
Does Prof. Dakin suppose that raw youths dissect 
fewer humans because they dissect more frogs ? 
I gather that he disapproves of attempts by me to 
discuss evolution, ‘‘ for his letter indicates a very 
imperfect acquaintance with biologists and_ their 
work.”’ I think by biologists he means zoologists 
and botanists. But, if I be incapable, why not end 
the nuisance by indicating my errors. A jury always 
grows suspicious when not the evidence, but only the 
opposing attorney is attacked. There has been much 
of this hinting at my ignorance—doubtless with 
reason, if not with proof. Nevertheless, I know some 
elementary facts which, it seems, are outside the range 
of the average naturalist, e.g., that events do not 
happen (characters do not develop) without ante- 
cedents (nature) and exciting causes (nurture) ; 
that living beings are bundles of adaptations; that the 
multicellular organism springs from a germ in which 
are none of the characters it afterwards develops, 
and therefore, inherits nothing but its nature (the 
sum of its potentialities for development), and 
develops nothing except in response to nurture; that 
our powers of observation are proportionate to our 
familiarity with the objects of study ; that whenever 
we are able to observe sufficiently closely we always 
| find natural selection in full swing; that the varia- 
| tions selected by Nature are always fluctuations ; 
that the result is always adaptive evolution; that 
man, unlike Nature, frequently selects mutations ; 
that therein lies the difference between natural and 
| artificial selection; and so on. 
On these elementary facts I have founded some — 
equally elementary questions. Why are some char- 
| acters supposed to be more innate, or acquired, or 
inheritable than others? What precisely was the 
great Lamarckian controversy about ? 
founded on anything but a play on words ? 
the word inherit used with two directly contrary 
meanings ? What is meant by the statement that 
“Nature is five perhaps ten times stronger than 
nurture,’’ and what by the statement that “ muta- 
| tions, but not fluctuations, have their representatives — 
Very obviously our whole immediate knowledge of | 
in the germplasm’? Why, in the face of enormously 
massive evidence, is it supposed that there is no 
natural selection, or that natural selection is merely a 
preserver, not a creator, of adaptations ? Why in 
the face of equally massive evidence is it maintained 
that the inheritance, not merely the reproduction, 
of mutations is independent ? And so on. I notice 
that the erudite people who are so ready to proclaim 
my ignorance are not equally ready to face these 
facts and answer these questions. Nevertheless, both 
facts and questions, however elementary, are funda- 
mental. Unless they be met, posterity will regard a 
page of Darwin, who always met his difficulties with — 
candour and without arrogance, of more value than all 
Was it 
Why is — 
+ ah aaa D am 

