Will and Desire

Physiologists should think before putting down the instinct of self-preservation as the cardinal instinct of an organic being. A living thing seeks above all to discharge its strength—life itself is will to power; self-preservation is only one of the indirect and most frequent results.
– Friedrich Nietzsche, Beyond Good and Evil

From Wikipedia, the free encyclopedia:

Schopenhauer posited a will to live, in which living things were motivated by sustaining and developing their own lives. Nietzsche instead posited a will to power, a significant point of contrast to Schopenhauer's ideation, in which living things are not just driven by the mere need to stay alive, but in fact by a greater need to wield and use power, to grow, to expend their strength, and, possibly, to subsume other "wills" in the process. Thus, Nietzsche regarded such a "will to live" as secondary to the primary "will to power", and more generally there are varied manifestations of it, two prominent distinctions by Nietzsche are: a "life-denying" modality and a life-"enhancing" or -"affirming" one. Henceforth, he opposed himself to social Darwinism, as he contested the validity of the concept of "adaptation", which he considered a narrow and weak "will to live".

Another particular standpoint of the will to power is that it is a process of expansion and venting of creative energy that Nietzsche argued was the underlying – the "most fundamental fact" – "inner" force of nature.