264 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
of man, of the breast-gland of modern women, etc. The fact that 
degeneration generally progresses so slowly, often taking thousands 
and thousands of years, seemed to him a sufficient proof of the inade- 
quacy of the Lamarckian explanation. For if the effect of disuse were 
transmitted in accumulating ratio in the successive generations, a 
useless organ ought to disappear much more quickly. 
“Weismann originally attributed a great effect to panmixia, and 
considered that nearly 90 per cent. of the reduction of rudimentary 
organs was due to it; the remainder, up to the complete loss of the 
organs, being accounted for by reversed selection. Romanes was 
much more modest in his estimate, and only allowed about 10 to 20 
per cent. to this cause; while Lloyd Morgan gave only 5 per cent. 
reduction of the original size. The final reduction of the organ to 
zero is still not accounted for by any of these theories. Calling to aid 
a failure of the force of heredity, as Romanes did, can hardly be con- 
sidered a solution of the problem. First of all, the force of heredity 
does not explain anything in the case. It only restates the problem. 
We want to know what the force of heredity is. Secondly, if the force 
of heredity does fail, we should have to explain why it wanes in some 
cases and notinothers. For the reduction and elimination of rudimen- 
tary organs occurs apparently in the most irregular, haphazard manner. 
“But can panmixia really reduce an organ? Plate, in agreement 
with Spencer, Eimer, and others, denies any such possibility. An 
organ in a given condition of its existence varies around a mean or 
average, the plus and minus variations generally being equally fre- 
quent. It follows, therefore, that if all the existing variations are 
crossed in propagation, the organ remains stationary. Selection only 
improves the organ by cutting off the minus variations; the absence 
of selection would simply leave the organ where it was before the 
selection. At most it could only sink a very little below the aver- 
age. That this is so is seen in organs which are not under the sway of 
selection at all. There are numberless such indifferent species charac- 
ters, which ought gradually to dwindle and disappear, yet they remain 
fairly constant, though continually exposed to the swamping effect 
of panmixia. Panmixia may explain the functional degeneration of 
an organ, but cannot explain its actual rudimentation. 
“Weismann himself in later times abandoned panmixia as a suffi- 
cient means of explanation, and resorted to a new theory—that of 
germinal selection.’ 
From S. Herbert, First Principles of Evolution (1913). 
