Parallel Evolution On Venus?

Thesis: in Golden Age sf, space explorers uncritically accepted the existence of Earth-like organisms, including even beautiful princesses, on other planets;

Antithesis: in more recent, more realistic sf, they do not find any such organisms;

Synthesis: in SM Stirling's The Sky People (New York, 2006), they do find such organisms and are extremely puzzled by them.

Even with panspermia or microbes on meteors:

"'...evolution's a chaotic process; you get general similarities, but not identities...'" (p. 25)

So what is the explanation? Maybe separate evolution can reproduce exact details or:

"'...maybe the God-did-it crowd is right -'
"'Them!'" (p. 26)

At this early stage of the novel, certain principles are clear:

the characters need to do more research;
"'...evidence first, theory second...'" (ibid.);
I expect the author to make some explanation to the reader even if the characters remain in the dark;
an author can base a fiction on any premise - CS Lewis presents divinely created human beings on Venus;
however, Stirling writes in the hard sf tradition of Poul Anderson, not in the theological sf tradition of CS Lewis.