Victorian society was shocked when Sigmund Freud said that all human endeavor is motivated by sex and death. Libido is to sex/creation/life/growth as Destrudo is to pain/breakage/death/corruption.
Animals exercise libido pretty directly in mating and play, whereas humans can (and sometimes do) sublimate the libido into acts of artistic, scientific, philosophical, or social creativity.
The Sponsorâ„¢-approved outlets for libido are work, acquisition, and sex (gotta keep 'em classically conditioned).

I stand corrected. Thank you, Wigs. =)