In evolutionary psychology, people often speak of the four Fs which are said to be the four basic and most primal drives (motivations or instincts) that animals (including humans) are evolutionarily adapted to have, follow, and achieve: fighting, fleeing, feeding and fucking (a more polite synonym is the word "mating").
Conventionally, the four Fs were described as adaptations which helped the organism to find food, avoid danger, defend its territory, et cetera.
[4] In the case of vertebrates, this list corresponds to the motivational behaviours that drive the activity in the hypothalamus, namely: fighting, fleeing, feeding and sexual functioning.
The hypothalamus responds to these motivations by regulating activity in the endocrine system to release hormones to alter the behaviour of the animal.
When the lateral areas of the hypothalamus were treated with electrical brain stimulation (EBS), the animals would start eating uncontrollably, which resulted in gaining excess weight rapidly.