Scientists Suspect Genetic Underpinnings to Human Monogamy

A groundbreaking study from a Harvard University team suggests that monogamy may be genetically programmed within some mammals.

Cute couple has their love lock on a bridge.
Cute couple. Getty Images.

Evolutionary anthropology has for some time tried to understand what natural relationship pattern humans follow, if there is one. In his book Sex at Dawn psychologist Christopher Ryan posits that our prehistoric ancestors practiced multiple kinds of sexual and romantic relationships.


Monogamy became a social institution and one that made sense. Polygamy was the most common practice in the ancient world, but it made women a commodity. Rich men could keep multiple wives for themselves, whole harems, which caused a lot of strife among others, fighting over those who were left. Monogamy however, eliminated this problem and helped seed societal stability.

Even so, multiple societies around the world still practice different forms of pair bonding other than monogamy. Even the most strident monogamist will admit that marriage can prove difficult. There’s things like the four year slump and the seven year itch. Some evolutionary biologists have explained these as a cessation of the pair bonding process.

When we were hunter-gatherers, we traveled in tight-knit bands. Children were raised not only by their parents but by the whole village itself. When the child was old enough to be a little more independent, the parents were free to go off and explore other relationships.

According to renowned anthropologist and love expert Dr. Helen Fisher, there are actually four different, unique personality types when it comes to human love. Each is driven by a preponderance of a certain neurochemical or hormone in the person’s system. And some are better suited for monogamy than others.

In this case, nature may have made some people naturally polyamorous and others monogamous, to ensure stability for raising children, while at other times, ensuring variety within the gene pool and to that end, aiding our survival.

Is there an evolutionary basis for cheating? Getty Images.

Now, a groundbreaking study published in the journal Nature suggests that monogamy may be genetically programmed within us, or at least in mice, to ensure offspring receive proper care. “Parental care is essential for the survival of mammals, yet the mechanisms underlying its evolution remain largely unknown,” the authors write. Researchers at Harvard University studied two breeds of mice to arrive at this conclusion.  

The first was the oldfield mouse (Peromyscus polionotus), one of those rare monogamous animals. Only 5% of mammals practice monogamy. Both sexes of this breed are known to be doting parents. They will, together, build an elaborate nest for their young and lick or clean them.

The second breed was the deer mouse (Peromyscus maniculatus), who are promiscuous by nature, and look upon their oldfield cousins as helicopter parents. In most mammalian relationships, males mate with as many females as possible, but do little to help raise the offspring. What researchers discovered, by looking at these two mouse breeds, was distinct genetic variations, which coincided with each type’s relationship style.

Hopi E. Hoekstra was the senior author of the study. She’s an evolutionary biologist. Though oldfield and deer mice won’t mate in the wild, if a male and female are put into the same tank alone together, they will. The resulting offspring are healthy. It was a variety of such hybrids that led them to understand whether or not parenting and relationship styles are genetically influenced.

Is monogamy in our nature, polyamory, or a combination? Getty Images. 

In a previous study, Hoekstra and her team took the pups of each type of mouse and placed them in each other’s nest. Researchers wanted to know if the mice acted this way because they were raised to tend to pups, or if each breed of mouse had an instinctual parenting style. The latter proved true. Once this was found, researchers went about investigating each type’s DNA.

They bred five mice, who created 30 hybrid offspring. These were bred and another 769 hybrid mice were born. Researchers looked at the second and third generations, to see what type of parenting each took up. Some put in minimal effort, others were completely aloof, and others still attentive parents. This wide variety of styles allowed researchers to hone into the mice’s DNA and find the differences. They came upon 12 areas or loci which were associated with parental instincts.

Researchers found that one loci controlled just one behavior, nest building, while others controlled more than one. These loci varied in terms of sex. One loci when activated, seemed to make fathers more attentive, but not mothers. Unfortunately, each loci carries many genes, so it’s hard to hunt down which is responsible for what behavior.

In their most recent study, these Harvard researchers looked at one biochemical in particular, vasopressin. This is a bonding neurotransmitter in many species, including rats and humans. Deer mice contain three times the amounts as oldfield mice, however. To find out what role it played, researchers injected oldfield mice with it. Instead of elaborate nests, they acted more like deer mice, and made simple ones. Yet, in terms of care, they were still doting parents.

Studies show that some may be better suited for monogamy than others. Getty Images.

According to their genetic research, the vasopressin gene only accounts for 6.7% of nest building instincts in male oldfield mice, and 2.9% in females. This opens the door to whether or not human pair bonding and parenting could be influenced by an instinct imprinted on our DNA. Though we’re a far cry from mice, we share many of the same neurotransmitters and hormones, along with other mammals.

Differences in biochemical makeup or neurotransmitters may signal how a species cares for its young, and whether it’s monogamous, promiscuous, or a mixture of the two. In exploring other species and working our way up, we may find out more about ourselves, even what relationship pattern or parenting style works best. Perhaps, we’ll find the genetic underpinnings of Dr. Fisher’s theory.

To learn what similar genetic underpinnings have so far been identified in our species, click here: 

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A landslide is imminent and so is its tsunami

An open letter predicts that a massive wall of rock is about to plunge into Barry Arm Fjord in Alaska.

Image source: Christian Zimmerman/USGS/Big Think
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  • A remote area visited by tourists and cruises, and home to fishing villages, is about to be visited by a devastating tsunami.
  • A wall of rock exposed by a receding glacier is about crash into the waters below.
  • Glaciers hold such areas together — and when they're gone, bad stuff can be left behind.

The Barry Glacier gives its name to Alaska's Barry Arm Fjord, and a new open letter forecasts trouble ahead.

Thanks to global warming, the glacier has been retreating, so far removing two-thirds of its support for a steep mile-long slope, or scarp, containing perhaps 500 million cubic meters of material. (Think the Hoover Dam times several hundred.) The slope has been moving slowly since 1957, but scientists say it's become an avalanche waiting to happen, maybe within the next year, and likely within 20. When it does come crashing down into the fjord, it could set in motion a frightening tsunami overwhelming the fjord's normally peaceful waters .

"It could happen anytime, but the risk just goes way up as this glacier recedes," says hydrologist Anna Liljedahl of Woods Hole, one of the signatories to the letter.

The Barry Arm Fjord

Camping on the fjord's Black Sand Beach

Image source: Matt Zimmerman

The Barry Arm Fjord is a stretch of water between the Harriman Fjord and the Port Wills Fjord, located at the northwest corner of the well-known Prince William Sound. It's a beautiful area, home to a few hundred people supporting the local fishing industry, and it's also a popular destination for tourists — its Black Sand Beach is one of Alaska's most scenic — and cruise ships.

Not Alaska’s first watery rodeo, but likely the biggest

Image source: whrc.org

There have been at least two similar events in the state's recent history, though not on such a massive scale. On July 9, 1958, an earthquake nearby caused 40 million cubic yards of rock to suddenly slide 2,000 feet down into Lituya Bay, producing a tsunami whose peak waves reportedly reached 1,720 feet in height. By the time the wall of water reached the mouth of the bay, it was still 75 feet high. At Taan Fjord in 2015, a landslide caused a tsunami that crested at 600 feet. Both of these events thankfully occurred in sparsely populated areas, so few fatalities occurred.

The Barry Arm event will be larger than either of these by far.

"This is an enormous slope — the mass that could fail weighs over a billion tonnes," said geologist Dave Petley, speaking to Earther. "The internal structure of that rock mass, which will determine whether it collapses, is very complex. At the moment we don't know enough about it to be able to forecast its future behavior."

Outside of Alaska, on the west coast of Greenland, a landslide-produced tsunami towered 300 feet high, obliterating a fishing village in its path.

What the letter predicts for Barry Arm Fjord

Moving slowly at first...

Image source: whrc.org

"The effects would be especially severe near where the landslide enters the water at the head of Barry Arm. Additionally, areas of shallow water, or low-lying land near the shore, would be in danger even further from the source. A minor failure may not produce significant impacts beyond the inner parts of the fiord, while a complete failure could be destructive throughout Barry Arm, Harriman Fiord, and parts of Port Wells. Our initial results show complex impacts further from the landslide than Barry Arm, with over 30 foot waves in some distant bays, including Whittier."

The discovery of the impeding landslide began with an observation by the sister of geologist Hig Higman of Ground Truth, an organization in Seldovia, Alaska. Artist Valisa Higman was vacationing in the area and sent her brother some photos of worrying fractures she noticed in the slope, taken while she was on a boat cruising the fjord.

Higman confirmed his sister's hunch via available satellite imagery and, digging deeper, found that between 2009 and 2015 the slope had moved 600 feet downhill, leaving a prominent scar.

Ohio State's Chunli Dai unearthed a connection between the movement and the receding of the Barry Glacier. Comparison of the Barry Arm slope with other similar areas, combined with computer modeling of the possible resulting tsunamis, led to the publication of the group's letter.

While the full group of signatories from 14 organizations and institutions has only been working on the situation for a month, the implications were immediately clear. The signers include experts from Ohio State University, the University of Southern California, and the Anchorage and Fairbanks campuses of the University of Alaska.

Once informed of the open letter's contents, the Alaska's Department of Natural Resources immediately released a warning that "an increasingly likely landslide could generate a wave with devastating effects on fishermen and recreationalists."

How do you prepare for something like this?

Image source: whrc.org

The obvious question is what can be done to prepare for the landslide and tsunami? For one thing, there's more to understand about the upcoming event, and the researchers lay out their plan in the letter:

"To inform and refine hazard mitigation efforts, we would like to pursue several lines of investigation: Detect changes in the slope that might forewarn of a landslide, better understand what could trigger a landslide, and refine tsunami model projections. By mapping the landslide and nearby terrain, both above and below sea level, we can more accurately determine the basic physical dimensions of the landslide. This can be paired with GPS and seismic measurements made over time to see how the slope responds to changes in the glacier and to events like rainstorms and earthquakes. Field and satellite data can support near-real time hazard monitoring, while computer models of landslide and tsunami scenarios can help identify specific places that are most at risk."

In the letter, the authors reached out to those living in and visiting the area, asking, "What specific questions are most important to you?" and "What could be done to reduce the danger to people who want to visit or work in Barry Arm?" They also invited locals to let them know about any changes, including even small rock-falls and landslides.

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