In humans
When speaking of animals with the ability to reason (generally considered the exclusive domain of humans), goals are no longer limited to short term satisfaction of basic drives. Nevertheless, there remains a strong relationship of happiness to goal fulfillment and the brain's reinforcement mechanism, even if the goals themselves may be more complex and/or cerebral, longer term, and less selfish than a non-human animal's goals might be.
Philosophers observe that short-term gratification, while briefly generating happiness, often requires a trade-off with negative repercussions in the long run. Examples of this could be said to include developing technology and equipment that makes life easier but over time ends up harming the environment, causing illness or wasting financial or other resources. Various branches of philosophy, as well as some religious movements, suggest that "true" happiness only exists if it has no long-term detrimental effects. Classical Utilitarianism is a theory of ethics based on quantitative maximization of happiness.
From the observation that fish must become happy by swimming, and birds must become happy by flying, Aristotle points to the unique abilities of man as the route to happiness. Of all the animals only man can sit and contemplate reality. Of all the animals only man can develop social relations to the political level. Thus the contemplative life of a monk or professor, or the political life of a military commander or politician will be the happiest.
In contrast, Zhuangzi points out that only man is endowed with the ability necessary to generate complex language and thought--language and thought that can be used to distinguish between things and form dichotomies. These dichotomies then formed, man tries to find reasons to like one side of things and hate the other. Hence, he loses his ability to love freely, in true happiness, unlike animals.