Darwin's Publication of "On the Origin of Species" Was Hastened

Darwin's publication of "On the Origin of Species" was hastened by the work of a fellow naturalist, who had independently reached conclusions about the evolution of species that matched Darwin's own; both men observed that

A) catastrophism to be supported in the geological record.
B) species being fixed and constant in form.
C) fossils to be tricks of nature.
D) slow geological processes operating on the earth.
E) there was individual variation in appearance within a species.