138 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
to cave animals: ‘‘As it is difficult to imagine that eyes, though useless, could be in any way 
injurious to animals living in darkness, I attribute their loss wholly to disuse” (p. 142). On the 
next page he writes: “By the time that an animal had reached, after numberless generations, the 
deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and 
natural selection will often have effected other changes, such as an increase in the length of the 
antenna; or palpi, as a compensation for blindness.” 
It may be that the struggle for existence goes on even in the darkness of caves, and that the 
“ fittest ” of the limited population survive by reason of their adaptation to their untoward sur¬ 
roundings. How adverse to life of any sort caves are may be'realized when we consider that only 
the lowest plants, and only a very few of those, live in caves. Without doubt the germs of fungi 
and the seeds of the higher plants are carried into the caves by freshets in subterranean streams 
and through sink-holes. Why, in spite of the darkness, we should not find more fungi even, and 
why one or two of the green algse should not flourish in the pools and brooks of caves, or why the 
seeds of the higher plants should not germinate, even if the plants do not bear fruit, can only be 
explained by the absence of light; and perhaps this is an important cause of the absence of all 
plant life in the ocean below a depth of about 300 to 500 fathoms. Certainly there are ample 
means for the colonization of caves by vegetables; the temperature, moisture, and inorganic food 
are more favorable than the sum total of conditions on alpine summits or in the high polar regions, 
or in hot springs. 
Animal life can apparently withstand greater physical obstacles than vegetable. As regards 
the struggle for existence, it possibly exists to a limited extent in cave animals. There is 
probably not enough vegetable or decayed animal food for all the animals, and some may die of 
hunger. The carnivorous beetles and Arachuida perhaps have a less favorable chance to obtain 
living food than the Crustacea, for the blind crayfish have a tolerable abundance of food in the 
Cmcidotsea, perhaps the most abundant form found in caves containing underground waters. 
We may, with Darwin, for convenience, use the phrase “ natural selection ” to express the 
process by which the cave fauna was produced, but such a term to our mind expresses rather 
the result of a series of causes than a vera causa in itself. There is of course no doubt but that 
many animals carried by different means into caves cannot thrive there, and consequently die. It 
is only those which have been able, by certain peculiarities of their life in the upper world allied 
to cave existence, to adapt themselves to cave conditions, which permanently breed there. Such 
forms, it is convenient to say, have been by nature selected and are successful in colonizing the darkest 
and most forbidding and apparently hopeless corners in the earth’s crust. But such a phrase as 
“natural selection,” we repeat, does not to our mind definitely bring before us the actual working 
causes of the evolution of these cave organisms, and no one cause can apparently account for such 
a result. There is rather a complex assemblage of physical causes, all working together, to secure 
a harmonious result. The most important and potent of these causes, when we study them under 
such appreciable, because so extraordinary, conditions as the physical features of cave existence, 
would seem to be the following: 
1. Change in environment from light, even partial, to twilight or total darkness; and involving 
diminution of food, and compensation for the loss of certain organs by the hypertrophy of others. 
2. Disuse of certain organs. 
3. Adaptation, enabling the more plastic forms to survive and perpetuate their stock. 
4. Isolation, preventing intercrossing with out-of-door forms, thus insuring the permanency of 
the new varieties, species, or genera. 
5. Heredity, operating to secure for the future the permanence of the newly originated forms 
as long as the physical conditions remain the same. 
Natural selection, perhaps, expresses the total result of the working of these five factors, 
rather than being an efficient cause in itself; or at least constitutes the last term in a series of 
causes. Hence Lamarckianism in a modern form; or, as we have termed it, Neolamarckianism, 
seems to us to be nearer the truth than Darwinism proper or “ natural selection.” 
The factors of organic evolution such as we have mentioned are of course theoretical, and the 
critic or unbeliever in a theory of descent demands facts in demonstration of the truth of the 
