CHAPTER XVIII 
OTHER THEORIES OF SPECIES-FORMING 
H. H. N. 
THEORIES AUXILIARY TO NATURAL SELECTION 
The post-Darwinian causo-mechanical theories fall quite naturally 
into two categories: those that were devised by Darwinians to bolster 
up natural selection and to free it of some of its most obvious objec- 
tions, while retaining the essential features of the principle; and those 
that were meant to be substitutes for and therefore quite opposed to 
natural selection. The former theories have been classed as auxiliary, 
and the latter as alternative theories to natural selection: 
The several theories of Weismann will be dealt with first as the 
most important of the purely auxiliary theories. ‘‘Panmixia”’ is 
designed to explain, without recourse to Lamarckism and in harmony 
with natural selection, the degeneration or atrophy of organs which 
seemed to be inadequately explained by Darwin. “Germinal Selec- 
tion” is supposed to explain the initial stages of adaptations and 
allied phenomena, and thus to aid natural selection at one of its 
weakest points. 
WEISMANN’S THEORY OF PANMIXIA 
The following statement of “ panmixia,”’ as given by S. Herbert, is 
concise and to the point: 
“Cessation of selection as a cause of atrophy was first proposed 
by Romanes. Later on, Weismann, whilst examining the validity of 
the principle of use-inheritance, adopted the same idea, called by him 
*panmixia,’ in order to account for the dwindling and disappearance 
of useless organs without having recourse to the Lamarckian factors. 
If natural selection leads to the mating of select types, so that those 
below a certain standard are prevented from propagating, it follows 
that, with the cessation of selection, a general crossing of all types, 
including the inferior ones, must take place, and thus lower the average 
quality of the whole stock. Weismann explained in this manner, for 
instance, the prevalence of short-sightedness among civilized people. 
The individuals with defective eyesight not being weeded out in 
modern society, the sharpness of the eyesight of the population sinks 
gradually. The same would apply to the deterioration of the teeth 
263 
