Rich or poor, urban or rural, educated or not, most of us still watch our backs. Hundreds of thousands of years have not bred that out of us—we still want to be ready just in case some beast jumps out from behind a rock. That’s why we respond so strongly to news that seems to warn us about perceived danger. 

Thanks to advances in brain research, we now have proof that “the brain devotes more attention to anything that appears threatening,” says psychologist James Breckenridge. Our automatic vigilance for threat has given us an enormous survival advantage throughout the ages, he explains, and we now do it continuously, subconsciously, and at lightning speed.

In 1986 Iranian officials still referred to HIV/AIDS as “a Western disease” and refused even to acknowledge that it might exist in Iran. But twelve years later, Dr. Kamiar Alaei managed to convince a community it needed an AIDS clinic. 

Another decade later, you find needle exchange programs in Iran, and huge billboards advertising condoms in a country noted for sexual repression. It’s all about building trust, according to Alaei, and it doesn’t happen overnight.