Unnatural traits on NPCs are locked until researched [Career mode progression]

As an example things like Hermaphrodites, Males with boobs/vagina, females with dicks, unnatural colors, maybe hybrid species, and all that jazz, basically any unnatural combination are locked and you won't encounter them until you do some SCIENCE and by extension develop drugs and treatments that would allow these kind of unnatural combinations to show up in your client browser. 

You can also go so far as to have clients that come in natural with a desire for these changes (which could be non physical as well ie: sensitivity, preferences etc).

and even going further as locking some customization option for the player character until the PC can alter him/herself to have those traits.