A scan of all the mutations in the human gene map shows something surprising – people of European descent are evolving fast, and not for the better.

The study finds that in the past 5,000 years, European-Americans have developed a huge batch of potentially harmful genetic mutations – many more than African-Americans.

The study, published in the journal Nature, may help explain why so many people develop diseases even though they don’t have common genetic mutations. It can also help explain why different people have so many different reactions to the same drug, said Joshua Akey of the University of Washington in Seattle who led the study.

It likely has to do with population explosion, Akey said. European populations expanded after the Ice Age ended and prosperous agricultural societies emerged. “The number of mutations that exist is directly attributable to the population growth that happened in the last 5,000 years,” Akey told NBC News.

“The things that allowed us to go from millions to billions of has also been the same process that has been pumping in all these new mutations.”

Akey and colleagues at genetics institutions across the country examined the gene sequences of more than 6,500 people – more than 4,200 European-Americans and 2,200 African-Americans. They were looking for small changes in the genetic code called single nucleotide variants – one-letter differences in the genetic code of A,C, T and G.

They found “an enormous excess of rare variants” in the European-Americans. And 73 percent of these mutations only appeared in the human genome in the past 5,000 to 10,000 years. Most were mutations that are known to weaken proteins, Akey said, and most of these harmful mutations were also in the people of European descent.

Now researchers are working to see which of these mutations might be associated with diseases. But many are in known disease-causing genes, such as the LAMC1 gene associated with premature ovarian failure, LRP1, which is linked with both Alzheimer’s disease and obesity and the CPE gene linked to hardening of the arteries.

Most are rare mutations – meaning they only affect a few people. “Some genes might be more disease-causing than other genes,” Akey said.

It may explain why it’s been so hard to find clear genetic links to many diseases. “We have been looking for disease risk where it isn’t,’ he said. “The last five to 10 years have been dominated by looking for common genetic variations that dominate common diseases. There is a lot of disease risk that is unexplained. Maybe there are classes of mutations that haven’t been looked at.”

The findings could explain why some people can smoke for a lifetime and never get lung cancer or heart disease, while someone else might suffer a heart attack despite having healthy blood pressure and cholesterol levels.

It definitely shows evolution in action, Akey said. “It’s just the process of evolution playing out in real time,” he said. “The dramatic population expansions that occurred over the past couple thousand years had a profound consequence on our genetic variability.”

Genetic mutations usually occur by accident – they are just mistakes that get made when DNA gets copied. They become important to evolution when they affect a person’s ability to survive and have children. The expansion of civilization, and the ability of societies to care for people who are less fit, was probably a factor in allowing these mutations to spring up, Akey said. “I think that is undoubtedly true,” he said.

Some of the genes identified in the scan also affect peoples’ response to drugs. That could explain why some people are helped, for example, by a cholesterol-lowering drug while others may not be. There wouldn’t have been much “selective pressure” on these genes before the modern drug era, but that doesn’t mean the genes were not influenced by something else. “It turns out that genes involved in adverse drug responses also have different biological roles,” Akey said – for instance, detoxifying certain foods.

There may even be more evolution in the future, Akey predicted. One example – phenylketonuria or PKU. It’s caused by a mutation in a gene that breaks down an amino acid called phenylalanine. People with PKU mutations must eat a strict, low-protein diet or they can develop seizures and mental retardation.

Now newborns are routinely tested for PKU so they can start the diet immediately and avoid any brain damage. Akey said because these kids can now grow up and lead normal lives, they will likely start having children and the gene may become more common in the population.

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This, finally, may explain our cultural obsession with zombies: Long after dark, millions of Americans basically become one.

Without warning, they suddenly rise from their silent, supine states then roam aimlessly, eyes open and mouths sputtering gibberish.

About 8.5 million U.S. adults -- or 3.6 percent of the grownup population -- have taken at least one sleepwalking jaunt during the past year, according to research released today by the Stanford University School of Medicine. That figure, calculated via a survey of nearly 20,000 people, means there are far more nocturnal wanderers than scientists previously suspected.

“It’s something, we were thinking, that was not frequent among the general population. And here, big surprise, it is,” said Dr. Maurice Ohayon, professor of psychiatry and behavioral sciences at Stanford and lead author of the paper. A previous report done a decade ago in European adults showed that 2 percent of that population were sleepwalkers. “It’s astonishing.”

The finding offers American doctors their first, solid sleepwalking benchmark, Ohayon said. Earlier speculation on how often the phenomenon occurred were based on anecdotal clinical reports as well as court cases and media tales of people who had gone sleep-driving, sleep-shopping or sleep-eating. Typically, those more sensational examples were linked to Ambien use.

But Ohayon and his colleagues found no significant link between prescription sleeping pills and increased sleepwalking. What they did discover: Folks who take certain anti-depressants (selective serotonin reuptake inhibitors, or SSRIs) are three times more likely to also take a snoozy stroll than the general population, and people who swallow over-the-counter sleeping pills have a higher likelihood of experiencing sleepwalking episodes at least twice a month month.

Brand names for anti-depressants in the SSRI category include Prozac, Zoloft, Paxil, Lexapro and Celexa. Non-prescription sleep aids linked to increased sleepwalking by the Stanford team contained diphenhydramine. Products laced with that chemical include 40 Winks, Simply Sleep, Sleep-Eze, Sominex, Unisom Sleep, Advil PM, and Tylenol PM, according to the National Institutes of Health. 

Chronic sleepwalking also runs (rambles?) within certain families, Ohayon learned: Nearly one-third of individuals who often do it can point to parents, grandparents, uncles, aunts or siblings who have a history of shuffling while slumbering.

To assess the sleepwalking rate in America, Ohayon and his Stanford colleagues used phone interviews conducted with 19,136 randomly selected individuals from 15 states. The participants offered baseline information on their mental health, medical histories and use of medications. They were quizzed on the frequency of any sleepwalking episodes as well as whether they had ever suffered any inappropriate or possibly perilous behaviors while asleep.

What's more, participants were asked if they'd sleepwalked when they were kids and if any family members were known to take unintended, nighttime strolls. In addition to the more more than 3 percent of the U.S. population who sleepwalk chronically, the researchers found that 29.2 percent of the test sample had gone sleepwalking at least once during their lives. 

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Robert Budd, a personal trainer from Southern California, takes sleeping strolls about once a month, as do almost all the men in his family.

Personal trainer Robert Budd figures he sleepwalks about once a month. When he gathers with his kin, sleepwalking lore is a common topic: while seemingly in dreamland, his grandfather once urinated in a friend’s drawer, his uncle often meandered the decks of navy boats, and his dad dismantled tents and ceiling fans.

“All the boys in the family do it,” said Budd, who operates a gym called PHYZYKS in Encinitas, Calif. “I've done it since I was a kid. I would walk out the door and my parents had to grab me and get be back inside. The commonality with my family and myself is it seems to happen when we’re really tired, really drained. When you really need sleep, that’s when you get up and sleepwalk.”

Budd has sleepwalked out of a tent at the Grand Canyon (on the floor, not near the rim). His friends spotted him heading off alone -- apparently wide awake -- but he remembered nothing the next day. While dozing, he once packed for a vacation, even remembering his toothbrush. And there was the night he tried to climb out a second-floor window only to be stopped by the woman who is now his ex-wife.

Was that intended exit possibly symbolic, even for a sleeping man? “It might have been,” Budd said with a laugh.

“It drives my girlfriend drives nuts because sometimes we have conversations and she doesn’t know if I’m awake. Like, I can’t be accountable in the middle of the night.”

Sleepwalkers typically have their eyes open and may speak, making detection tricky. But Ohayon isn’t certain, he said, if they are actually seeing what’s in front of them or if sleepwalkers’ brains have simply mapped out their homes in their minds, allowing them not to bump into walls or furniture. He is sure they’re not dreaming, though, because sleepwalking coincides with a period of “slow-wave sleep” or SWS when brain activity is diminished.

During another sleep phase called REM (rapid eye movement), brain neurons are firing as if a person is awake. This is when you dream. A mechanism within the brain blocks stirring and shifting when you’re in REM sleep, Ohayon said.

“During slow wave sleep, you can move,” he added. “This is an old function of our brain, (possibly a evolutionary leftover). You know, when birds fly, they can sleep with one half of their brain, while the other half is analyzing the flight.

“That is why you see the bird going for thousand of kilometers without any problem. They sleep when they fly.”

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