Talwin: A Terrestroid Planet

A Circus of Hells.

"Life on Talwin had followed the same general course as on most terrestroid planets."

-CHAPTER THIRTEEN, p. 290.

Is there a general course and, if so, what is it? When he wrote this, Poul Anderson was generalizing from a single instance.

"...the standard division into photosynthetic vegetable and oxygen-breathing animal had occurred,..." (ibid.)

Is this division standard? And, even if it is, does the next proposition follow?

"...and the larger animals were structurally familiar with their interior skeletons, four limbs, paired eyes and ears." (ibid.)

Differences:

although tissues are principally built of L-amino proteins in water solution, they normally metabolize levo sugars;

Merseians and human beings must avoid some native foods and also need dietary supplements;

we were told in CHAPTER ELEVEN that vegetation is mostly blue because the photosynthetic molecule is not chlorophyll although probably closely related.

Why is Talwin so Earth-like? The answer may simply be that many planets are not but a few are.