Darwin was not an atheist.
"In the second edition of January 1860, Darwin quoted Kingsley as “a celebrated cleric”, and added the phrase “by the Creator” to the closing sentence, which from then on read “life, with its several powers, having been originally breathed by the Creator into a few forms or into one”. While some commentators have taken this as a concession to religion that Darwin later regretted, Darwin’s view at the time was of God creating life through the laws of nature, and even in the first edition there are several references to “creation”."
Darwin was more or less a watered down Christian. So it's clear Janet decided to put an atheist narrative in there.