Ammonite

Change or die. These are the only options available on the planet Jeep. Centuries earlier, a deadly virus shattered the original colony, killing the men and forever altering the few surviving women. Now, generations after the colony has lost touch with the rest of humanity, a company arrives to exploit Jeep - and its forces find themselves fighting for their lives. Terrified of spreading the virus, the company abandons its employees, leaving them afraid and isolated from the natives.
In the face of this crisis, anthropologist Marghe Taishan arrives to test a new vaccine. As she risks death to uncover the women's biological secret, she finds that she, too, is changing - and realizes that not only has she found a home on Jeep, but that she alone carries the seeds of its destruction ... Winner of the James Tiptree, Jr. Award 1993