All tagged the broca divide

Stargate SG-1 Episode 1.04: "The Broca Divide"

SG-1 travels to a planet where it appears to be perpetually night, with SG-3's marines for back-up. There, they learn the planet's unfortunate situation--occasionally, humans here fall victim to a "curse" that turns them into the Neanderthal-like people, and they are exiled to the planet's night side. That would be all well and good, but when SG-1 and SG-3 return to Earth, the team members begin succumbing to the disease one by one.