366 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
for existence, any variation however slight, and from whatever cause 
proceeding, if it be in any degree profitable to an individual of any 
species in its infinitely complex relation to other beings, and to its 
environment, will tend to protect that individual and will generally 
be inherited by its offspring. Darwin calls the principle by which 
each slight useful variation of an organism was preserved, the principle 
of natural selection, in order to emphasize its relation to man’s power 
of selective breeding. For it s well known that by careful selection 
of the stock, we can adapt organic beings to our own use through 
the accumulation of slight but useful variations. Natural selection, 
however, is a power constantly ready for action, and is as immeas- 
urably superior to man’s efforts as the work of nature is to that 
of art.’ 
Darwin repeatedly insists on the fact that natural selection could 
not have been effective, unless very long periods of time were allowed 
_for its complete action. It is evident that time must have been an 
all-important factor if we are to suppose, that by the interaction of 
the inherent properties possessed by the elements of living organic 
matter, its structural arrangement became gradually modified in 
such a way, that the existing classes of animals and plants have been 
evolved out of it. For, as the late Prof. Huxley states, natural 
selection implies not only the existence of organic matter, but also 
its tendency to transmit its properties, and its tendency occasionally 
to vary; and lastly, given the conditions of existence, that these 
put together are the cause of the present and the past conditions of 
organic nature. 
The only evidence we can bring to bear on the subject of the pro- 
gressive evolution of the animal kingdom is derived from a study of 
their fossil remains, in the various geological strata of our own, and 
_ other parts of the world. The length of time these strata have 
taken to form is an open question, but we may be sure that our 
chalk rocks, for instance, consist of the shells of marine species of 
animals, and that these remains of once living beings must have 
taken long periods of time to have been deposited layer upon layer at 
the bottom of thesea. Darwin states that: the fineness of gradation in 
the shells of successive substages of the chalk formations led him 
to maintain the gradual as against the sudden evolution of species. 
The fossil shells in these rocks have been thoroughly investigated by 
Mr. A. W. Rowe, who states that ‘‘the white chalk of England offers 
1 On the Origin of Species by Means of Natural Selection, by Charles Darwin, M. A., 1859, p. 61. 
2 Many of the attacks made upon the hypothesis of natural selection have been founded on the imper- 
fection of geological records to show the transitional links, which, according to this theory, must have 
connected the closely allied species of animals. If, however, we take into account the perishable nature of 
the bodies and limbs of these creatures, the probable changes that have occurred in the surface of the earth 
since thay were deposited, and the imperfect state of our geological records, we can readily understand the 
reason for there being missing links in the fossil remains of former geological periods. 
