A group of monkeys is challenging humans’ views on sexuality by showing that same-sex behavior among males strengthens their social networks and may even help them father more offspring.
The findings, reported this month in the journal Nature Ecology and Evolution, suggest that same-sex behavior is not only natural in the animal kingdom, it can be socially advantageous.
The study “puts to rest the doubts of same-sex behavior occurring naturally in nature,” said senior author Vincent Savolainen, a biology researcher at Imperial College London.
Rhesus macaques monkeys grooming each other. A new study examining same-sex behavior among a colony of rhesus macaques is challenging humans’ views on sexuality.
Scientists have observed same-sex sexual behavior among more than 1,500 animal species, including penguins, giraffes and elephants. But it was unclear whether this behavior was widespread, if it was influenced by genetics and to what degree it might affect the reproductive success of the population as a whole.
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“We suspected same-sex behavior occurred in these macaques, but we didn’t know how common it was, or the partnership that it develops,” Savolainen said.
To find out, he and his colleagues visited a colony of about 1,700 free-range rhesus macaques living on a wildlife preserve in Puerto Rico. The colony has been monitored for the last 67 years, providing researchers with a comprehensive family tree of the primates.
The researchers defined same-sex behavior as the act of mounting because it was the most frequent — and most identifiable — form of sexual contact. Although it occurs in both male and female macaques, it is much more frequent in males.
Over three years, the study team observed 236 males who belonged to two distinct social groups within the colony. During that time, they documented 1,739 instances of mounting — 722 involving male-female pairs and 1,017 involving same-sex pairs.
The research team had expected to catch some same-sex couples in action, and Savolainen said he wasn’t surprised that their pairings outnumbered those of male-female couples.
Among male macaques, same-sex sexual behavior isn’t necessarily about sex, but more about social interaction. Male macaques mounted each other after grooming, eating, fighting, playing and resting as well as while traveling, according to the study. The activity could be a way to strengthen bonds between males, making them more likely to form alliances and ultimately gain access to more females, the researchers said.
It is important to note that the same-sex socio-sexual behavior observed in the study is distinct from homosexual behavior because its motivation and purpose are social, said Jean-Baptiste Leca, who studies primate behavior at the University of Lethbridge in Canada and was not involved in the new research. To be classified as true homosexual behavior, the form, motivation and function would all have to be sexual in nature, he said. As far as the researchers could tell, only one of the 236 macaques they studied engaged exclusively with other males.
The younger a macaque, the more likely he was to engage in same-sex encounters, the study authors found. That could be a sign that in some cases, the couplings “could partially function as ‘practice’ for future reproductive activity,” they wrote.
Indeed, engaging in same-sex mounting did not negatively affect a macaque’s overall reproductive success. After examining the offspring count for all 236 males, the researchers found that the more times a monkey paired up with a fellow male, the higher his offspring count tended to be.
The trend wasn’t statistically significant, but it was enough to confirm that same-sex behavior didn’t have a reproductive cost — something that Savolainen said he was surprised to find. Perhaps the stronger social bonds formed during these sexual encounters strengthened their coalitions and ultimately gave participants greater access to females, the researchers wrote.
By examining the behaviors of related macaques over multiple generations, the study authors determined that about 6% of same-sex sexual behavior could be explained by genetics. Though this may not seem like a lot, it’s comparable to the genetic component of complex behaviors in humans and other primates, such as grooming or alloparenting, which is care provided by individuals other than parents, Savolainen said.
Savolainen and his colleagues warned that the behaviors they observed in the Puerto Rico macaques might be specific to that population. Regardless, they said, the findings challenge the assumption that same-sex sexual behavior is rare in non-human animals and that it results in fewer offspring. Others agreed.
“This study contributes to our understanding of animal behavior,” said Rachna Reddy, a primatologist at the University of Utah not involved in the study. “Now we’re seeing that (same-sex) behavior is really frequent, occurs in lots of species, may have many functions, and that it’s not always costly.”
Meet the Japanese macaques of Jigokudani Monkey Park
Intro
The Japanese macaques in Jigokudani Monkey Park begin most days with a relaxing dip in their own private hot tub.
Located in Joshinetsu Kogen National Park in Japan's Nagano prefecture, the primate-only onsen is world-famous as the preferred simian hot spring.
But life hasn't always been so simple for the snow monkeys of Jigokudani ("The Valley of Hell," named for its natural hot springs). They were initially forced from their habitat in the 1950s by the development of nearby ski resorts.
As a result, they moved into nearby towns and quickly found trouble, raiding fruit from local farmers' orchards. The farmers petitioned the government and were granted the right to hunt the macaques.
A Nagano Railway Company worker and local nature enthusiast, Sogo Hara was determined to protect the monkeys and worked for months to persuade troops to leave the creatures alone. Hara's strategy was to lure the monkeys into the mountains with apples.
His group soon discovered a nearby ryokan (a traditional Japanese inn). As is typical for ryokans, Korakukan's property included outdoor onsen for guests' enjoyment. One day in 1963, so the story goes, an errant apple fell into the human's onsen. A young monkey tested the steamy water and emerged with the apple. He didn't exit the waters immediately, though, and many of the monkeys looked on as their buddy quietly enjoyed the water.
It wasn't long before other young monkeys began mimicking the water-loving monkey's behavior.
Within months, all of the female monkeys had taken to bathing in the hot springs. While this behavior delighted human visitors, it created a clear hygiene issue for the inn.
This led to the establishment of the Jigokudani Monkey Park in 1964, thanks to the efforts of Hara. Today, this is where the snow monkeys live, freely soaking in their dedicated hot springs peacefully.
Damage resulting from Typhoon No. 19 had impacted the spring's water levels and temperature but restoration work is now underway and the park is open to tourists.
The Jigokudani Facebook page offers daily updates on the restoration work and presence of the monkeys.
A relaxing soak
Japanese macaques in Nagano love soaking in onsen in the park that was made for them: Jigokudani Monkey Park.
The snow monkeys' onsen practice isn't solely about warming their bodies or bobbing for apples -- like the Japanese and visitors to Japan, they seem to appreciate onsen for its stress-reducing properties.
Since the macaque's thick coats keep them warm, and they take a dip even when there are no apples in sight, researchers' studying the monkeys at Jigokudani believe hot springs function primarily to ease their tension.
Staff encourage the macaques to keep the park's onsen in their daily routine, offering a steady diet of soybeans, barley and, of course, apples.
Researchers also discovered the monkeys' indifference to the nearly 500 daily visitors to the park. In other words, their stress hormones did not increase as the number of park visitors increased.
Even during the busy tourist season, the monkeys meander nonchalantly about the park, climbing in and out of the hot spring as humans snap photos and ooh and ahh in delight.
Unlike some of Japan's other open animal experiences, such as Nara Deer Park, touching or feeding the monkeys is strictly prohibited. But this rule doesn't detract from the joy of sitting poolside as the macaque play leapfrog.
Meet the monkeys
The baby monkeys love a good snow romp.
Since the monkeys don't swim every day (in spite of their warm fur coats, they seem to prefer the hot springs on colder days), visitors will want to plan accordingly before heading north to the park.
A flexible itinerary is best, and January and February are prime visiting months. Fresh snow is ideal -- the monkeys are at home and perhaps at their playful best in the snowy climate. If you're lucky, you might even catch baby monkeys wrestling and making snowballs.
Time of day is a critical piece of planning, too: Jigokudani Monkey Park requires an overnight stay to catch the monkey's early morning soak. While it is possible to do it as a day trip from Tokyo, even catching the earliest train will make for a later arrival, when crowds are at their greatest, and that's if everything goes off without a hitch. If you miss seeing the monkeys, you'll wish you had allowed for more time.
The park opens at 9 a.m. and closes at 4 p.m. daily, with extended hours from 8.30 a.m. to 5 p.m. seasonally.
You're better off arriving the night before you plan to visit. Stay at a ryokan, delight in its onsen and take off for the park first thing in the morning. If you can, leave time for onsen exploration beyond your ryokan, for at the base of the mountain leading to the park is a main street packed with nine unique onsens for weary travelers.
Each meant to aid a particular ailment, the onsen encourage visitors to walk the charming street in a yukata (light kimono) and wooden sandals to collect stamps on a towel passport from all the onsens. Doing so is believed to ward off evil spirits and bring divine favor. The thin strip contains no shortage of mom-and-pop restaurants eager to share their house-made versions of Japanese staples.
Getting there
Most of these inns offer complimentary morning shuttles to the Jigokudani Monkey Park's information center. To best even these crowds, early risers can trek up the scenic path themselves for a chance at some private time with the monkeys.
From the information center, the monkey's onsen is only accessible via a one-mile path through the forest, about 30 minutes each way. Unfortunately, Jigokudani Monkey Park is not accessible to wheelchairs as the final ascent consists of tight winding paths and steep steps.
Jigokudani Monkey Park's pool-side views offers visitors a delightful insight into this unique behavior. Relaxing with the chilled-out macaques is a quintessential excursion from Japan's mega-cities.
Getting to Jigokudani Monkey Park from Tokyo requires an hour and a half ride on the shinkansen (high speed train) to Nagano, then a 50-minute trip on a local train to Yudanaka station in Yamanouchi, the town the park is located in. The Jigokudani Monkey Park information center is two miles from the train station.
For winter enthusiasts exploring nearby Shiga Kogen, the largest ski field in Asia, it's less than a hour's bus ride away.
