What does Nick compare human kind to

Nick compares human kind, both past and present, to Gatsby.

Gatsby believed in the green light, the orgastic future that year by year recedes before us. It eluded us then, but that's no matter—tomorrow we will run faster, stretch out our arms farther. . . . And one fine morning——

So we beat on, boats against the current, borne back ceaselessly into the past.