Intervening sequences of regularly spaced prokaryotic repeats derive from foreign genetic elements.

Order of authorship in the original publication: Mojica, Díez-Villaseñor, Jesus García-Martínez. In this paper Mojica and colleagues showed the the CRISPR system is a bacterial immune system against viral attack. This was the first evidence that bacteria have an immune system. A consequence of this discovery is the implication that the human immune system could have begun evolving billions of years ago in bacteria.

(Thanks to Juan Weiss for this reference and its interpretation.)