Full text: Problems in eugenics

52Section I.R. Pearl. 
From this table it is in the first place clear that the number of oocytes in 
the ovary of a hen is very large; much larger, I think, than has generally 
been supposed. While to be sure there are for the most part only vague 
statements respecting this point in the literature, usually these statements 
are to the effect that the bird’s ovary contains “ several hundred ” ova. 
Not only is the absolute number of oocytes large, but it is also very much 
larger than the number of eggs which any hen ever lays. A record of 200 
eggs in the year is a high record of fecundity for the domestic fowl, though 
in exceptional cases it may go even a hundred eggs higher than this. But 
even a 200-egg record is only a little more than a tenth of the average total 
number of visible oocytes in a bird’s ovary, to say nothing of the probably 
much larger number of oocytes invisible to the unaided eye, but capable of 
growth and development. In other words it is quite evident from these 
figures that the potential “ anatomical ” fecundity is very much higher than 
the actually realized fecundity. This is true even if we suppose the bird to 
be allowed to live until it dies a natural death. 
An examination of the table in detail indicates that there is no very close 
or definite relationship between the number of visible oocytes in the ovary 
and the winter production of a bird. Thus No. 1367 and No. 3546 each 
have about the same number of visible oocytes, yet one has a winter 
production record 18 times as great as the other. Again, No. 71 with the 
extraordinarily high winter record of 106 eggs has only a little more than 
one-half as many visible oocytes as hen No. 2067, whose winter production 
record is only 32 eggs. Again No. 71 with its 106 record has very nearly 
the same oocyte count as No. 8010 with a winter record of zero. In general 
it may be said that the present figures give no indication that there is any 
correlation between fecundity as measured by winter production, and the 
number of oocytes in the ovary. Of course, the present statistics are 
meagre. More ample figures are needed (and are being collected) from 
which to measure the correlation between actual and “ anatomical ,y 
fecundity. The data now in hand however indicate clearly, it seems to me, that 
there must be some other factor than the anatomical one involved in the 
existence of different degrees of actual fecundity in the domestic fowl. It 
evidently is the case that when one bird has a winter record of twice what 
another bird has it is not because the first has twice as many oocytes in the 
ovary. On the contrary it appears that all birds have an anatomical 
endowment entirely sufficient for a very high degree of fecundity, and in 
point of fact quite equal to that possessed by birds which actually 
accomplish a high degree of fecundity. Whether or not such high fecundity 
is actually realized evidently depends then upon the influence of additional 
factors beyond the anatomical basis. As has already been indicated in the 
preceding section it is reasonable to suppose that these factors are 
physiological in nature.

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