darwin's theory of natural selection. 
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DARWIN'S THEORY OE NATURAL SELECTION. 
ABSTRACT OF REV. C. CROFT'S PAPER. 
(Read December 12th, 1872.) 
The Lecturer referred to the views which were generally accepted 
before Mr. Darwin's theory was given to the public, and to the 
modification which they underwent in consequence of geology 
bringing to light former assemblages of life. Mr. Darwin taught 
that species are not produced by distinct creative acts, but by 
the modification of other species under favourable circumstances. 
Minute differences, so trifling as to be almost undiscoverable to 
the unpractised eye, are continually occurring in all species. 
Amidst hundreds of these slight divergencies, one or two might 
chance to give the animal or plant some advantage in the great 
struggle for existence, and thereby insure its survival, and the 
perpetuation of its accidental peculiarity, probably in an intensified 
form. This divergence from the parent type would at length 
amount to a variety — then to a species — then possibly would give 
rise to a new genus. Quicker powers of motion, stronger or longer 
weapons for seizing prey, or more inconspicuous colouring, might 
be advantageous circumstances, insuring the survival of their 
possessors when less favoured forms would become extinct. The 
same tendency which permitted the formation of varieties would 
also permit the formation of species and genera, unless there were 
some mysterious limits beyond which divergence could not be 
carried. Lamarck's theory took into account the formative power 
of external conditions, which in his opinion gave rise to continued 
improvement and advance in organization ; but as low forms of 
life are now, as heretofore, in existence, he was compelled to 
account for them by the continued creation of " monads." 
The lecturer now mentioned some of the arguments by which 
the theory of natural selection is usually supported. (1) There 
was no special fitness in the forms inhabiting any district, to the 
conditions in which they were placed, as shown by the fact that 
they are frequently supplanted by other forms artificially intro- 
