Hainish Cycle - Biology

Biology

Most of the people in the tales have a common descent from the planet Hain, which settled many surrounding worlds. Some of them are genetically similar enough to produce children together. The unusual hairyness of the Cetians is mentioned in The Word for World is Forest and The Dispossessed - though to Cetians, it seems that other types of human have unusually little hair. The Telling includes the detail that the people of Chiffewar are all bald.

There are some cases of ancient biological manipulation:

• Unique among known humans, the Hainish have complete voluntary control of their fertility. In order for a Hainish man and woman to reproduce, they must both consciously choose to produce viable genetic material, which they learn to do in adolescence. The required genetic changes to the Hainish population were made in the far distant past, and apparently took many generations to accomplish.
• The Left Hand of Darkness mentions that the 'hilfs of S' must have been produced by human genetic manipulation by the ancient Hainish people, along with the Gethenians and the degenerate winged hominoids of Rokanan.
• The hermaphrodite humans of Gethen may have been produced as an adaptation to a harsh climate, or an experiment to see how people would live without gender. Both ideas are mentioned and nothing is definitely settled.
• The degenerate winged hominoids are seen in Rocannon's World. They live in cities that require much higher technology to build than the rest of the races on Rokanan, but live in bat-like societies, hunting for humans and animals on which their larvae feed by sucking their blood.
• We hear no more about the 'hilfs of S', unless these are the same as the small furry natives of Athshe (who are of Hainish descent, like the various other humans and quasi-humans).
• The Matter of Seggri tells us that the extreme gender imbalance of the people of Seggri may be another case of genetic manipulation.

Alterrans with their distinctive cat-like eyes are nevertheless able to breed with Earth-humans. They may be another case of genetic manipulation, or a natural adaptation.

The Shing of City of Illusions seem to be of some other origin: they cannot interbreed with Earth-humans.