"[E]ach branch of knowledge studies a subset of reality that depends on factors studied in other branches. Atomic physics underlies the workings of chemistry, which studies emergent properties that in turn are the basis of biology. Psychology can no longer be separated from the study of properties emergent from the interaction of neurons and synapses. Sociology, economics, and anthropology are each, in turn, studies of properties emergent from the interaction of countless individual humans." - from WikipediaSee also: Consilience - The Unity of Knowledge
"SELFISH GENES": All creatures (including humans) are "survival machines" for their genes -- individuals are (in the bigger biological picture) irrelevant. The individual's only purpose is to ensure that his genes (wherever they may be located) are successfully passed on.
Individuals are not stable things, they are fleeting. Chromosomes too are shuffled to oblivion, like hands of cards soon after they are dealt. But the cards themselves survive the shuffling. The cards are the genes. The genes are not destroyed by crossing-over, they merely change partners and march on. Of course they march on. That is their business. They are the replicators and we are their survival machines. When we have served our purpose we are cast aside. But genes are denizens of geological time: genes are forever. - Dawkins, "The Selfish Gene"*****
"WILL TO POWER": All creatures are driven (by their genes) to control their environments, which include any other creatures with which they interact. Nietzsche's ideas on "Will to Power" come very close to describing/explaining these drives, although he was incorrect in his views contesting adaptation. The drive to control one's environment is there only to serve the goal of successfully passing on one's genes.
My idea is that every specific body strives to become master over all space and to extend its force (—its will to power) and to thrust back all that resists its extension. But it continually encounters similar efforts on the part of other bodies and ends by coming to an arrangement ("union") with those of them that are sufficiently related to it: thus they then conspire together for power. And the process goes on. - Nietzsche, "Will to Power"