From Creatures Wikia
A drive is a biological need. Drives are often graphically represented in the Creatures series by a bar, with green at one end (for not needing to do something), yellow in the middle, and red at the other end (indicating an urgent drive). The higher the concentration of the drive chemical, the more urgent the drive is - no matter how essential it is to survival! (See the Choice Norns). The drive lobe of the brain contains the current state of a creature's drives, and is monitored by the Health Kit and Science Kit in Creatures 1 and Creatures 2. The HoverDoc in Docking Station can monitor drives.
Drives are controlled in a set of three chemicals - a drive raising chemical (Boredom++ or Boredom Increase), a drive chemical (Boredom), and a drive lowering chemical (Boredom-- or Boredom Decrease). The drive raising chemical, when introduced into the metabolism of the creature, converts to the drive chemical and an amount of Punishment. The drive lowering chemical, when introduced into the metabolism of the creature, reacts with the drive chemical to produce Reward. Unnecessarily reducing a drive has no effect on the norn.
Steve Grand, in 1996, described this model as being "primitively Behaviorist", but noted that it provided a learned logic for creatures' decisions.
The drives present in C1 were Pain, Need for Pleasure, Hunger, Coldness, Hotness, Tiredness, Sleepiness, Loneliness, Crowdedness, Fear, Boredom, Anger, and Sex Drive. C2 retained all of the C1 drives and Injury, Suffocation, Thirst and Stress were added. In C3/DS, the drives were Pain, Hunger for Protein, Hunger for Carbohydrates/Starch, Hunger for Fat, Coldness, Hotness, Tiredness, Sleepiness, Loneliness, Crowdedness, Fear, Boredom, Anger, Sex Drive and Comfort/Homesickness.
If a creature has no drives, it does not feel the need to do anything - this is why gengineering your creatures to remove their need for food or making them super-resistant to disease can result in a very boring game!