I would take the validity of this excerpt with a grain of salt

Indeed. The quote was first published in 1957 and may be heavily outdated. I cannot judge for myself, because I know next to nothing about biology, but Asimov’s astronomical essays are plain wrong by today’s knowledge.

Also keep in mind that this was written for science fiction readers. So there are necessarily simplifications that may not survive close scrutiny (again: I’m not an expert here).