The Evolution Of Love

Not only are owl monkeys are monogamous, but the fathers perform many of the parenting duties. Photo Credit:

(ANIMAL SCIENCE/ANIMAL BEHAVIOR) Love is not usually thought of as an evolutionary development, yet this human trait may stem from pair bonding in other monogamous animals.

For instance, owl monkeys are known to have one mate for life. They do not cheat or “divorce,” and are completely committed to their significant other. This behavioral trait may be the evolutionary precursor to human love.

Read more about this exciting research and the progression of love, just in time for Valentine’s Day! — Global Animal

Not only are owl monkeys monogamous, but the fathers also perform many of the parenting duties. Photo Credit:

National Geographic News, Christine Dell’Amore

It may not seem like monkey business, but emotional bonds in animals such as primates may have evolved into love as we know it.

Take owl monkeys, tiny tropical tree-dwellers that treat every day like it’s Valentine’s Day. A male and a female stick together as long as possible, never cheat, and never “divorce” their mates—extremely unusual behavior, even among people. (Also see “Male Monkeys Wash With Urine to Attract Females?”)

Sometimes, though, young adult owl monkeys that can’t find mates—monkeys that scientists call floaters—pick vicious fights with established pairs, eventually kicking one of them out.

Now, new research shows that the monkeys forced to take on new partners have fewer babies than owl monkeys that haven’t been broken up, said Eduardo Fernandez-Duque, a biological anthropologist at the University of Pennsylvania in Philadelphia who led a new study on owl monkey relationships.

The results show how monogamy helps owl monkeys—and may even shed light on how human relationships evolved.

“Call it love, call it friendship, call it marriage—there is something in our biology that leads to this enduring, emotional bond between two individuals that is widespread among human societies,” Fernandez-Duque said in a statement.

Owl monkeys peek out of a tree in Yasuni National Park, Ecuador. Photo Credit: Tim Laman, National Geographic
Owl monkeys peek out of a tree in Yasuni National Park, Ecuador. Photo Credit: Tim Laman, National Geographic

Trouble in Paradise

Only about five percent of mammals are monogamous, and the phenomenon most often arises when both parents are needed to raise offspring, as in the case of people.

With owl monkeys, fathers take on most of the childcare after a baby is born, relying on the mother only for milk.

But floaters—which Fernandez-Duque and colleagues first noticed in 2003 in Argentina’s Chaco region (map)—can spell trouble in paradise.

Drawing on nearly two decades of observations of 18 owl monkey groups, the team discovered that pairs that stay intact produce 25 percent more babies than monkeys in severed pairs.

The exiled animal from those broken relationships, meanwhile, is usually injured and often dies.

Since the team studied more than 150 animals, “I felt very confident that what he was telling us is a real phenomenon—it’s not a flash in the pan,” noted Patricia Wright, who was one of the first people to study owl monkeys in the 1980s.

“He had the goods on the animals. I was really excited about that,” said Wright, an anthropologist at Stony Brook University in New York.

Wright said she was personally pleased that the study reinforced findings that owl monkeys stay true to one another unless forced to separate.

“I knew that these little monkeys didn’t fool around,” she said.

Owl monkeys forced to take on new partners have fewer babies than owl monkeys who haven’t broken up. Photo Credit:

Chemistry of Love

Why monkeys that are broken up have fewer babies is unknown, though Fernandez-Duque suspects there’s an emotional component. (See more pictures of all-star animal dads.)

Just as a man and a woman need time to get to know each other and form a deep connection, so do owl monkeys. So when a marauding monkey enters into a new relationship, there’s a delay in mating—usually about a year, Fernandez-Duque  said.

In fact, pair bonding in monogamous animals, such as owl monkeys, may be “sort of evolutionary antecedent to love in humans,” said Larry Young, a behavioral neuroscientist at Emory University in Atlanta and author of the new book The Chemistry Between Us: Love Sex and the Science of Attraction.

Young, who studies the brain chemistry of love and emotion, does most of his research on monogamous prairie voles.

Though human love is a rich emotion reflective of our advanced brains, he said, “the foundation of that emotion is very similar to the neuromechanisms that are causing the bond between these two prairie voles.”

For instance, experiments have shown that if a vole loses its partner, the “widowed” animal shows depressive symptoms—measured by a lack of willingness to escape a dangerous situation.

According to Young, our brains are in the love seat, so to speak: The organs “have evolved the mechanism to produce an emotional attachment,” he said.

That attachment is spurred by oxytocin—produced during intimate contact in both people and animals—and dopamine, which is responsible for feelings of exhilaration and happiness.

So, many splendored as it is, love, he said, “is really the result of a cocktail of chemicals.”

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  1. Somehow, it seems to me that love is more than just the result of a cocktail of chemicals, but the chemicals could be the result of our choice to love and the feelings that love arouses. Love, however, is more than just a feeling. Reducing everything to chemicals is silly. You can't tell whether the chemicals are the cause of the effect and it dehumanizes love. I guess if scientists really think they are nothing more than a bag of chemicals, it makes sense, but I can't believe that.