That's the current consensus age for the transition to the Cambrian Age, when the following quote indicates sexual reproduction first appeared:

Consider the following:

1. Previous life did not use sex as a means of reproduction
2. They replicated making exact copies of themselves
3. Genetic diversity was only increased by mutation and new chemical reactions occurring on Earth making simple proteins
4. More modern organisms share genetic information by sexual reproduction
5. 50% of genetic material is taken from each unique parent
6. The offspring is unique, containing only 50% of genetic material from each parent, plus any change caused by natural selection and mutations
7. Overall, diversity in the species is increased, causing differences, and thus selective advantages/advantages in comparison to one another within the species, and in relation to their environment

[source: Biology Online]

If a male mates with several females, he increases the number of his progeny, but for females it makes no difference. A female gains only a little from having a large number of copulations with different males. Therefore, males in general are promiscuous but females are choosy because they want their few progeny to be of highest possible quality. There is also another reason. In species where females invest more in offspring, females will be the choosier sex. Females, then, want to increase the quality of their progeny by mating with particular males rather than others. All other things being equal, males are under strong selection to mate with as many females as possible. The selection forces on females act to be selective in terms of which males father their progeny. In summary, eggs represent a limited resource for which males must compete. There is usually a trade-off between mating behavior and parental care.

[source: Sexual Selection"; M.Tevfik Dorak.]

I presume, in Lee's "brave" new world, the females would be choosing from a catalog (I've heard this is already the case with "sperm banks") ... and the choices will be limited.

On that note: here, for the edification of all not previously self-brainwashed, is a brief <a href=http://www.pbs.org/wgbh/evolution/darwin/nameof/">essay on eugenics, including the history of the movement. Here's a quote:

In the long run, human genetic knowledge will very likely lead to therapies and cures for many diseases. But some fear that the techniques of gene therapy, embryo selection, and the engineering of sperm could all become tools of a kind of human genetic manipulation that would be offensive to humane and egalitarian values. The manipulation could discriminate against socially costly or devalued groups and individuals.

"Some fear"... yeah, including me.