So, people's genes were altered in five ways that remove five different flaws from them, and these types of alterations are the five aptitudes.

Which means: people who a flaw was removed from had to have it. And they were probably chosen for that flaw to be taken away because it's the one they had the most.

Example: I want to see if it's possible to eliminate dishonesty from someone and if that would help the society. I must pick someone whose worst flaw it is, so it would be best seen if it was successful,. I do so and that very dishonest person is now apt for Candor.

Meaning: GD's aptitudes are for the virtues they'd have the least if they were GP.

The heck.