Reproductive suppression field

The Reproductive Suppression Field, or Suppression Field is one of the many tatics employed by the Combine the keep control of the population. As the name suggests this field blocks the ability humans to reproduce by prohibiting certain protein chains important to embryonic development from forming; thus the lack of childern on the streets of City 17. This would have ensured that the current generation of humans would have been the last on Earth.

During the fall of the Combine in the events of Episode 1 the Suppression Field failed, thus prompting Kleiner's speech urging the City 17 population to begin 'mating' for the 'survival of the species'.