For many people, the objective of playing with Norns is to breed more Norns. A knowledge of the ups and downs of the Norn's hormonal systems is very useful for this.

All Norns become fertile when they reach youth. In male Norns, fertility depends upon the testosterone chemical. The level of testosterone depends upon the Norn's age and general health. The larger the amount of testosterone, the more fertile the Norn. Female Norns also have a similar chemical, oestrogen. However, the levels of oestrogen cycle from high to low and back again. The female is only fertile when oestrogen is high.

When a Norn is fertile, it needs to find a mate in order to breed. They do this using pheromones. When a Norn is ready to mate, it produces an internal chemical called Arousal Potential. If a Norn is not ready to mate for any reason, it produces Libido Lowerer, which removes any sex drive and arousal potential from the Norn's system. If a creature of the opposite sex and the same species is near, their pheromones trigger production within the Norn of Opposite Sex pheromone. This reacts with Arousal Potential to create the Norn's sex drive. When the two Norns are 'friendly' enough, they will kisspop, and the female might get pregnant. It is possible to increase the likelihood of two Norns hitting it off using the HoverDoc. Place the HoverDoc over one of your candidates, and click the right hand arrow to slide out the options panel. Choose the bottom symbol, of the interlinked male and female icons. This will display a graph of the male or female hormones, depending on who the HoverDoc is looking at. The hormones are colour coded:

Dark Pink
Arousal Potential
Sex Drive
Opposite Sex Pheromone
Dark Blue
Libido Lowerer

You can encourage Norns to mate using the up and down arrow buttons on the HoverDoc display. These will inject the Norn with Arousal Potential and Sex drive. They are likely to go hunting for a mate soon afterwards!

If the female gets pregnant, a small egg will appear in the HoverDoc's icon of the Norn. During pregnancy, progesterone rises constantly. When it reaches a peak, the Norn will lay an egg. Progesterone, as well as tracking pregnancy, prevents the Norn being fertile while pregnant, and thus prevents multiple pregnancies. For a while after giving birth, the female is infertile, and slowly recovers her fertility over time.