NATURE 
197 

APRIL 
22 
Sy 
IQI5. 
THURSDAY, 


THE BIOLOGICAL PROBLEM. OF SEX. 
The Determination of Sex. By Dr. L. Doncaster. 
Pp. x+172. (Cambridge: At the University 
Press, 1914.) Price 7s. 6d. net. 
R. DONCASTER deals in a masterly way 
with a problem as difficult as it is fascin- 
ating, and his book is a fine illustration of scien- 
tific method. He states a theory and presents the 
evidence, and when the reader has just begun to 
enjoy a sense of satisfaction, more facts are 
brought forward which show that the theory 
breaks down, and that we have still much to 
learn eesti the determination of sex. It is a 
pleasure to follow a discussion which is so keenly 
critical and at the same time open-minded. Those 
who know Mr. Doncaster’s book on heredity will 
éxpect lucidity in his treatment of a cognate 
subject, and they will not be disappointed. He 
goes deeply into things, but it is all clear, includ- 
ing the glossary. The illustrations are interest- 
ing and instructive. An indication of the scope 
of the book may be given in the chapter-head- 
ings: The problem; the nature and function of 
sex; the stage of development at which sex is 
determined; sex-limited inheritance; the material 
basis of sex-determination; the sex-ratio; second- 
ary sexual characters; the hereditary transmission 
of secondary sexual characters; hermaphroditism 
and gynandromorphism ; general conclusions on the 
causes which determine sex; the determination of 
sex in man. The author does not deal with the sub- 
ject in its entirety, the case of plants, for instance, 
being deliberately left out, but selects for illus- 
tration and discussion the lines which seem to 
him most promising. 
Dr. Doncaster’s general position may be 
stated. In some cases sex appears to be deter- 
mined already in the unfertilised ovum, for male- 
producing and female-producing ova are formed. 
In other cases sex seems to depend on the sperma- 
tozoon, and to be fixed at fertilisation; thus, to 
take a simple case, the unfertilised ova of the 
hive bee develop into males, and there are many 
instances now known of two kinds of spermatozoa 
differing in respect of their chromosomes. In a 
few cases there is evidence that sex may be 
modified during embryonic development or even 
later. Many facts point to the conclusion that a 
sex-determining factor sometimes _ resides 
special sex chromosomes, and is inherited like a 
Mendelian character (as was first suggested by 
Bateson and by Castle). Individuals which receive 
it from both parents would be of one sex; 
NO. 2373, VOL. 95| 
in 
those | 
to which it is transmitted by one parent only 
would be of the other sex, f 
But the author goes on to point out that there 
are many facts which do not fit in with this 
theory. There is evidence that the ovum may 
influence the sex in cases in which observations 
on the chromosomes indicate that the sex should 
be determined by the spermatozoon; and there is 
evidence that the sex may in some cases be modi- 
fied after fertilisation by influences acting on the 
embryo or some later stage. Therefore the author 
is inclined to give up the simple hypothesis of an 
unchangeable hereditary entity, the presence of 
which always causes one sex and its absence the 
other. He supposes that sex is dependent on a 
physiological condition of the organism, depend- 
ing on the interaction of certain chromosomes 
with the protoplasm of the cells, and therefore 
determined, in the absence of other disturbing 
factors, by the presence or absence of these parti- 
cular chromosomes. But where the determina- 
tion expressed by the chromosome difference is 
not decisive, other conditions may have their 
influence. ‘Put in different words, every germ- 
cell would bear a sex-determining factor, but 
when this factor has relatively small intensity of 
action, its effect may be counterbalanced by other 
causes which alter the physiological relation on 
which sex-determination depends.” 
As to Man, the evidence from the study of 
chromosomes is at present unsatisfactory, but it 
is.maintained by some that Man is one of those 
species in which the male has one chromosome 
less than the female; all the ova contain an 
X-chromosome (supposed to have a sex-determin- 
ing function), while half of the spermatozoa have 
it and half have not. When two X-chromosomes 
are present in a fertilised ovum it. develops into 
a female; when only one, into a male. But apart 
from the chromosomes, there are some other facts 
which point to the conclusion indicated. The most 
important of these is the sex-limited transmission 
by the male, as seen in the inheritance of colour- 
blindness, night-blindness, and hemophilia. “If 
a man transmits certain characters always or 
nearly always to his daughters, the conclusion 
can hardly be avoided that he produces two kinds 
of germ-cells, female-producing which bear the 
factor for these characters, and male-producing 
which do not.” If sex in man is determined solely 
by the spermatozoon, ‘there is no hope either of 
influencing or of predicting it in special cases.” 
But if the ovum has some share in the effect, as 
some other facts suggest, if there are two kinds 
of ova, or if the physiological condition of the 
ova is alterable, the possibility of influencing the 
sex of the offspring through the mother is not 
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