SUCCESS IN CON TROLEING SEX 
Male-producing and Female-producing Eggs Regularly Distinct in Pigeons— 
Whitman-Riddle Experiments Result in Making Each Kind of Egg 
Produce Opposite Sex, Under Some Conditions—New View 
of Nature of Sex—Application to Human Society 
E TALK a good deal about the 
possibilities of sex-control— 
we who are interested in breed- 
ing. We would be much pleased 
if we could secure an excess of one sex, 
instead of the half-and-half which we 
usually get. If we could mate fowls in 
such a way as to produce nothing but 
males, or nothing but females, we would 
think we had reached the farthest goal 
conceivable—in that direction. 
But an approximation to such a re- 
sult has been obtained. Under excep- 
tional circumstances, it is true—but 
given those circumstances, it is being 
done continually. 
Professor C. O. Whitman, one of the 
greatest among the investigators and 
teachers of biology, who died in 1910, 
learned the basis upon which such 
matings may be made. After his death 
his work was continued by Dr. Oscar 
Riddle, who is getting the same results 
at the Carnegie Institution’s laboratory 
for the study of experimental evolution, 
in Cold Spring Harbor, Long Island. 
Dr. Riddle, moreover, undertook, and is 
still engaged in, a special study of many 
aspects of these matings, in an attempt 
to decide whether a real, or only an 
apparent, sex control is involved. His 
answer has already been given—a 
reversal of sex has been effected. The 
results of these investigations are not 
yet published, but from the addresses, 
abstracts and short papers of Dr. 
Riddle, beginning in 1911, a fairly 
comprehensive survey of results may 
now be obtained. 
To understand their results, let us 
first see what happens when we make 
a very wide cross in pigeons and doves, 
the material of their experiments. Or- 
dinarily breeders mate members of the 
same species. Sometimes we can mate 
158 
members of different species. Occa- 
sionally we can mate individuals of the 
next higher division, a genus; but we 
consider that a very wide cross. It is 
not often that we can go into the divi- 
sion above this, and mate members of 
two different families. But it can be 
done with pigeons. 
Now when birds (not hybrids) of two 
different families are mated, the off- 
spring produced are all males. In the 
whole history of the study there have 
been but two exceptions, and one at 
least of the females then produced was 
not perfect; the sexual development 
was rudimentary. 
Here, then, we have a certain kind 
of sex-control, for we find that we can 
produce all males from a cross of two 
different families. So wide a cross as 
that hardly ever takes place in artificial 
breeding, and probably much less often 
or never in nature. But it suggests to 
us that if we are to get an insight into 
sex-determination, we must depart from 
the normal conditions as far as possible. 
GENERIC CROSSES MADE 
Dr. Riddle has found it most conven- 
ient, in view of Whitman’s earlier re- 
sults, to work with crosses of two 
different genera. From such a mating, 
the eggs produced in spring and early 
summer hatch into all or nearly all 
males. But if such a pair of birds are 
made to “overwork at reproduction,” 
t. e. if they are not allowed to incubate 
their own eggs, and are made to lay eggs 
very rapidly, a pair each week or so, it 
will be found that as the season grows 
later, the eggs laid become progres- 
sively ‘‘weaker,’’ until those near the 
end of the laying period will hatch with 
difficulty or not at all. From those 
eggs that do hatch from the birds which 
