I am looking for a short story, as far as I remember only a few pages long. (From around the 1980s).
The story is set in the distant future, where humans have spread throughout the solar system (at least). A hostile alien race attacks the humans, who have no manner to defend themselves. However, a research team finds some information on another alien race that encountered the hostile aliens in the distant past. These other aliens do have information on a weapon used to defy the hostile aliens.
When the human research team finds the information, they learn that humans themselves were the weapon, as humans reproduce quickly in respect to the aliens, and are brutal fighters.