The ideas of Ernst Haeckel, in his youth a hardline Darwinian materialist, were to evolve to a surprising degree.
This form of objection left the door ajar to the kind of “hybrid” interpretation favored by some in both Britain and America in the later Victorian period.
Darwin began casting around in his mind for supplementary theories, sometimes going so far as to reconsider evolutionary thinking he had once firmly rejected.
Notoriously, one of the shrewdest of Darwin’s “reticences” concerned the lack of fossil evidence.
A colleague remarked to me (in an uncharacteristically unscholarly disclosure) that he could not share my interest in “all this old 19th-century stuff.”