In evolutionary biology, people often speak of the four Fs which are said to be the four basic drives (motivations or instincts) that animals (including humans) are evolutionarily adapted to have, follow, and achieve: fighting, fleeing, feeding and fucking. In the case of vertebrates, this list corresponds to the motivational behaviours that drive the activity in the hypothalamus, which responds to these motivations by regulating activity in the endocrine system and releasing hormones to alter the behaviour of the animal.
The list of the four activities appears to have been first introduced in the late 1950s and early 1960s in articles by psychologist Karl H. Pribram, with the fourth entry in the list sometimes being replaced by other terms such as "sex" or "mating and maternal behavior."