How to understand the grammar in this sentence?
Here are the passages: "For more, check out Morgan’s work in full on the Internet Archive, which includes lovely passages like this one, marveling at how beavers build dams even though they don’t have to:
"As the dam is not an absolute necessity to the beaver for the maintenance of his life, his normal habitation being rather natural ponds and rivers, and burrows in their banks, it is, in itself considered, a remarkable fact that he should have voluntarily transferred himself, by means of dams and ponds of his own construction, from a natural to an artificial mode of life."
In the sentence: "it is, in itself considered, a remarkable fact that he should have voluntarily transferred himself,...", why did the author use "should have voluntarily" rather than "should voluntarily"? I mean "should have transferred" means the beaver didn't construct the dam, right? It's weird to me. "it is, in itself condiered", why did the author use "it" , "itself" rather than "he" and "himself" in here?