Before you start rolling your eyes, this isn’t one of those sketchy studies like the one sponsored by Clorox to debunk the 5-second rule and thus promote super-clean floors. This one comes from a bona-fide nerd—a geneticist at Stanford University who just published a study in the science journal Trends in Genetics.

Although US News doesn’t detail his methodology much beyond citing “math,” according to Gerald Crabtree it’s almost mathematically certain that over the last three thousand years mutations affecting 5,000 genes in our DNA have evolved to make us dumber. Basically the movie “Idiocracy” is playing out in slow motion.

“I would wager that if an average citizen from Athens of 1000 BC were to suddenly appear among us, he or she would be among the brightest and most intellectually alive of our colleagues and companies, with a good memory, a broad range of ideas, and a clear-sighted view of important issues,” Crabtree says.

But, ah—you ask—if ancient man was so smart and we’re so stupid, why did we just discover penicillin in 1928 and why did ancient people think fruit flies spontaneously generated around bananas? Because that’s pretty dumb.

Apparently when we talk about the evolution of intelligence there are two things at play: cumulative knowledge transfer over generations, and actual organismic evolution of the brain. Technology author Jaron Lanier talks about generational knowledge in his book “You Are Not A Gadget” and speculates that if octopi weren’t born self-sufficient they’d be considered the smartest animals on the planet—it’s because humans are born dependent that we’re forced to hand knowledge from one genration to the next. Each generation starts with eons of accumulated knowledge, which is why even the dumbest person today knows that fruit flies do not spontaneously generate.

But in terms individual brain power, Crabtree says a weird thing is happening: the safer life gets for humans, the less intelligence and good judgement factor into survival and mating, and the more likely that “dumb genes” get passed on to the next generation. And since the last century has seen unprecedented safety and security for the masses, you’d think the rate of change on the dumb scale would be accelerating.

But Crabtree isn’t worried: “People 300 years ago had no idea where we’d be scientifically now,” he says. And because of the power of generational knowledge transfer we’ll be able to solve the problem of individual dumbness if it starts getting out of hand. “We’ll be able to deal with this problem with a range of humane and ethical solutions,” he says.

Presumably he’s not talking about putting down the dumb ones out back, Old Yeller style.