The analysis of the processes underlying such motivations can make use of research on animals, in ethology, comparative psychology, and physiological psychology, and the hormonal and brain processes involved in them seem to have much in common at least across all mammals and probably across all vertebrates.



However, in humans, even these basic fundamental motivations are modified and mediated through social and cultural influences of various kinds: for example no analysis of hunger in humans could ignore the issues of eating disorders such as anorexia nervosa and obesity, for which the parallels in other animals are unclear.

Even in animals, it is clear that the earlier homeostatic "depletion-repletion" models of such motivations are no longer adequate, since many animals feed on a precautionary rather than a reactive basis, most obviously when preparing for hibernation.

At the next level are motivations that have an obvious biological basis but are not required for the immediate survival of the organism. These include the powerful motivations for sex, parenting and aggression: again, the physiological bases of these are similar in humans and other animals, but the social complexities are greater in humans (or perhaps we just understand them better in our own species).

In these areas insights from behavioral ecology and sociobiology have offered new analyses of both animal and human behaviour in the last decades of the twentieth century, though the extension of sociobiological analyses to humans remains highly controversial. Perhaps similar, but perhaps at a rather different level, is the motivation for new stimulation - variously called exploration, curiosity, or arousal-seeking.

A crucial issue in the analysis of such motivations is whether they have a homeostatic component, so that they build up over time if not discharged; this idea was a key component of early twentieth century analyses of sex and aggression by, for example, Freud and Konrad Lorenz, and is a feature of much popular psychology of motivation.

The biological analyses of recent decades, however, imply that such motivations are situational, arising when they are (or seem to be) needed to ensure an animal's fitness, and subsiding without consequences when the occasion for them pases.

The most obvious form of motivation is coercion, where the avoidance of pain or other negative consequences has an immediate effect. When such coercion is permanent, it is considered slavery.

While coercion is considered morally reprehensible in many philosophies, it is widely practiced on prisoners or in the form of conscription. Critics of modern capitalism charge that without social safety networks, wage slavery is inevitable. Successful coercion sometimes can take priority over other types of motivation.