Germs, Not True Love, Make Humans Mate for Life

Havoc caused by sexually transmitted diseases convinced our ancestors it would be better to mate for life. Continue reading →

Why did humans become monogamous, apparently rejecting the promiscuity that is natural to most animals?

Was it morality? Religion? Maybe love?

The answer is germs, researchers said Tuesday, arguing that the havoc caused by sexually transmitted diseases (STIs) convinced our ancestors it would be better to mate for life.

A research duo from Canada and Germany observed that STIs flourished among large groups of people living in the villages, towns and cities that arose after prehistoric hunter-gatherers settled down to farm.

Left unchecked, spreading diseases can affect individual fertility and a group's overall reproduction rate.

Falling population numbers would force a rethink of sexual behavior - which in turn gives rise to social mores.

The researchers developed a mathematical model of hunter-gatherer demographics and likely STI spread among them.

They used it "to show how growing STI disease burden in larger residential group sizes can foster the emergence of socially imposed monogamy in human mating."

In small groups of no more than 30 individuals, with no chance for epidemic spread, STI outbreaks are generally short-lived, the team said.

The reduced risk may explain why small groups, both among early humans and today, are often polygynous (when men have more than one partner).

‘Evolutionary puzzle'

Socially-imposed human monogamy has long been considered an "evolutionary puzzle," according to the research duo.

It requires societies to put in place checks and structures - a police and court system, for example - to uphold societal mores.

"Yet, many larger human societies transitioned from polygyny to socially imposed monogamy beginning with the advent of agriculture and larger residential groups," said the paper.

That riddle may now be solved.

The research showed that our natural environment, with factors such as disease spread, "can strongly influence the development of social norms, and in particular our group-oriented judgements," study author Chris Bauch of the University of Waterloo in Canada told AFP.

But this did not necessarily mean that humans would become wildly promiscuous if drugs were to make STIs a thing of the past, he added.

"Modern societies are more complicated... and there is probably more than one reason that explains socially imposed monogamy," Bauch said by email.

"I think it is premature to speculate that marriage will disappear, or that polygyny will return, if we solve the problem of STIs."

The research was published in the journal Nature Communications.

Dr. Tom Frieden, director of the Centers for Disease Control and Prevention (CDC), told Discovery News that "2015 was a very active year for protecting Americans." Indeed, there were plenty of crises and near-crises that threatened our health. Here's a sampling of six scares from 2015. In the meantime, the World Health Organization has already

issued a list of the top diseases on its watchlist

for 2016. For the second year, Ebola dominated global health issues. At the CDC, over 4,000 staff members, or 20 percent of the staff, worked on curtailing the outbreak, Frieden said. "The thing that is least well understood about Ebola is how close it became to a global catastrophe," Frieden said. "It could have been widespread in Africa for years, and it would have killed people not just from Ebola, but because health systems stop functioning." In fact, in Guinea,

more people died of malaria than Ebola

, because the country's health care system was so overloaded with Ebola patients that people with other diseases couldn't get proper treatment. "Ebola is an epidemic that not only kills but undermines others," Frieden said.

10 Things That Kill the Ebola Virus

Over 15,000 Americans died from

Clostridium difficile


C. difficile

) in a single year; it causes more hospital-acquired infections than any other bacteria, according to a CDC study. Not only do people often contract it when they are on antibiotics; some strains are resistant to treatment from antibiotics, making fecal transplants the leading alternative treatment. But the scariest bacteria news of 2015 might be the recent finding that a superbug gene found in China quickly infected someone in Denmark, highlighting the risk that drug-resistant bacteria pose to most modern medicine. "I'm an infectious disease physician and I have treated many people with cancer who are getting chemotherapy and have had horrible infections held in check with antibiotics," Frieden said. "If we don't have antibiotics, then cancer and other [modern medical treatments] are hanging by a thread." Waiting for a new miracle drug is a mistake, he added; it's also essential to take "better stewardship of the antibiotics we have."

New Resistant Superbug Spreading

Air pollution is a silent killer, said Dr. Francesca Dominici, a professor of biostatistics at the Harvard T.H. Chan School of Public Health. But there's no escaping it. "With air, you cannot wake up one morning and say you're not going to breathe or even move somewhere with clean air," she said. "It's affecting everybody." There is an antidote, however: "If we shut down coal-fired power plants, it would save lives immediately," she said. "But it's the one thing no one is talking about." Climate change talk tends to focus on the future, what life will be like in 100 years. But there is a "health crisis happening right now," she said, and "it's crazy to think people are not doing anything about it. In a certain way, not acting on air quality and power plants is like not acting on the Ebola epidemic." When coal-fired power plants are shut down, the ambient air improves immediately, she said. Air pollution is linked to cardiovascular disease, which is the No. 1 killer in the U.S. It's also associated with lung function and cognitive issues in children.

Air Pollution in China Kills Millions Annually

Although it didn't cause any deaths, the measles outbreak traced to Disneyland grabbed headlines across the country and put the debate about vaccines back in the spotlight. Many of the 147 people who fell sick were not immunized against measles, either for personal beliefs or because they were too young to get the vaccine. Vaccines in the U.S. are "underused," Frieden said. Take the HPV vaccine, which is recommended for girls and boys at age 11 or 12: according to a 2014 survey, 40 percent of girls and 60 percent of boys hadn't started the 3-shot series. "We're doing less well that Rwanda at protecting our children against HPV," he said. About 25 percent of Americans are infected with HPV, which can cause several types of cancer.

5 Disease Outbreaks Linked to Vaccine-Shy Parents

Each year, more than 200,000 people die from preventable medical errors, killing more Americans than anything except for heart disease and cancer. "Considering we're all going to get sick at some point and need a hospital, it's hard to think we could suffer from error, and care that is not coordinated as it should be," Dominici said. Errors include everything from giving patients the wrong medication to giving premature babies too much oxygen.

Mistakes Made In Half of All Surgeries

When 180 people in one small town in Indiana were infected with HIV in less than a year, it drew national attention. In a county that typically sees fewer than five cases of HIV a year, most of the new cases were linked to partners injecting the prescription opioid oxymorphone with shared syringes. Opioid pain relievers are prescribed for reducing severe pain, but "we got the risk-benefit wrong," Frieden said. "There's a short-term benefit, but in the medium- and long-term, you could die from it." The painkillers are so addictive that 1.9 million Americans live with prescription opioid abuse or dependence, and there are thousands of overdose deaths in the U.S. per year. The 2015 Indiana State Department of Health investigation reveals additional risks, including a resurgence of HIV.

Video: Big Leap Toward HIV Cure