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The excerpt represents the core issue or deciding factor on which you must meditate, and is drawn from On the Origin of Species by Charles Darwin: species have fixed and definite characters. Genera which are polymorphic
in one country seem to be, with some few exceptions, polymorphic in other
countries, and likewise, judging from Brachiopod shells, at former periods
of time. These facts seem to be very perplexing, for they seem to show
that this kind of variability is independent of the conditions of life. I
am inclined to suspect that we see in these polymorphic genera variations
in points of structure which are of no service or disservice to the
species, and which consequently have not been seized on and rendered
definite by natural selection, as hereafter will be explained.
Those forms which possess in some considerable degree the character of
species, but which are so closely similar to some other forms, or are so
On the Origin of Species |
