Charles Lyell, Historian of Time's Cycle - Time's Arrow, Time's Cycle: Myth and Metaphor in the Discovery of Geological Time - page 168

albeit with great reluctance, that apparent progress in life's history was also a
reality after all.
Lyell held firm for more than twenty years, from the first edition of the
Principles in 1830 to his last defense of nonprogression in an anniversary
address as president of the Geological Society of London in 1851. But twenty
years of exploration had uncovered no Paleozoic mammals, and his old
argument—that we had no right to expect any while our knowledge of
Paleozoic times rested upon just a few oceanic sediments of limited
geographic extent—became less and less defensible as studies of Paleozoic
geology spread into eastern Europe and North America. Lyell began to
waver, and eventually, during a painful process extending through the 1850s,
he surrendered.
While Lyell believed that no human remains, or even artifacts, graced the
geological record, he could view Homo sapiens as God's addition of the last
moment. But as undoubted artifacts were unearthed from the youngest strata,
Lyell could no longer deny that human origin had been an event in the
ordinary course of nature. How could he then deny progress as a guiding
principle? Thus, when Lyell gathered his material on human history into a
separate volume in 1862 ( On the Geological Evidences of the Antiquity of
Man ), he wrote that progress in life's history was "an indispensable
hypothesis . . . [which] will never be overthrown."
As for the Principles, Lyell had published his ninth edition in 1853, last to
defend the strict version of time's cycle. He then waited thirteen years, far
longer than the time to any previous revision, to bring forth the tenth edition
in 1866—the first to announce his retreat. I have no doubt that this long
interval records his growing doubt and confusion, his unwillingness to
commit himself once again in print until he had resolved this crucial
dilemma. The eleventh edition, last of Lyell's lifetime, appeared in 1872,
with only minor revisions from his key capitulation in 1866.
Chapter 9 of this last edition still treats the same subject—"theory of the
progressive development of organic life"—ut this time Lyell assents. In the
summary of his closing paragraph, Lyell finally untangles the conflation of
methodological and substantive uni-