Who’s your daddy? If you’re a gorilla, it doesn’t matter
New research shows rank matters more than paternity for males’ relationships with infants
By Lucy Goodchild van Hilten Posted on 17 June 2015
A large male mountain gorilla sits next to the baby of the group, painstakingly picking away at the baby’s head: it’s grooming time in the forest, and the gorilla daddy is doing his duty.
Or is he the daddy? New research says it doesn’t really matter – it’s the male gorilla’s rank in the group that makes the difference when it comes to bonding with the kids.
A new study published in Animal Behaviour shows that higher-ranking gorillas form stronger relationships with infants, regardless of whether they are related. The authors, from the University of California, Los Angeles, the Dian Fossey Gorilla Fund International in Atlanta and the Max Planck Institute for Evolutionary Anthropology in Leipzig say their findings support the theory that for most of their evolution, gorillas lived in groups with one male and several females.
Mountain gorillas – Gorilla beringei beringei – live in groups in the forests of central Africa. One group, or troop, of gorillas can have more than one male as well as several females. However, scientists believe that this has not always been the case; earlier in their evolution, mountain gorillas may have lived in troops with only one male and several females.
For the new study, researchers tracked the way male mountain gorillas interact with infants to see if their behavior is similar to other primates that live in troops with more than one male. The results show that being the biological father does not influence the way male gorillas interact with infants, suggesting that their social structure is relatively new.
“For a long time there was an assumption that monkeys and apes didn’t know who their fathers were in groups with multiple males,” said lead author Dr. Stacy Rosenbaum, a biological anthropologist at Lincoln Park Zoo in Chicago. “Thanks to advances in molecular genetics, we now know that’s not always true, though in this particular species, it turns out that assumption was correct.”
Behavioral evidence for social change
Scientists often refer to gorillas’ physical features as evidence of their previous history of living in groups with only one male. The main characteristic is the difference in size between males and females, which is called sexual dimorphism: males are up to twice as big as females, which is the biggest size difference of any living primate.
[pullquote align="right"]"Gorillas are very special animals. ... You look at them and start to see your own behavior differently."[/pullquote]
Male gorillas also have huge canines and thick muscle on their heads, which makes them better fighters. When living in groups with only one male, gorillas would need to fight to get females from other groups, and to defend females in their own group. They also have very small testicles relative to their body size, and their sperm swim slowly – probably because historically there was little sperm competition from other males.
The new study is the first behavioral evidence to support the theory. Primates like chimpanzees that live in troops with more than one male have a way of recognizing which infants belong to which males. For animals that live in groups with only one male, this is not necessary because the male is most likely the father of all the infants in the group. The researchers wanted to determine whether gorillas have evolved a way of recognizing their own offspring or father.
They analyzed more than 1,500 hours of data and found that there is no evidence to suggest that gorillas have a way of recognizing their own offspring or father. Instead, they found that a male gorilla’s dominance rank had a stronger influence on its relationships with infants; alpha males tend to be more nurturing and have stronger relationships with infants in the troop. While statistically they are the most likely father, many infants are sired by other males.
Gorillas are charismatic research subjects
The researchers followed gorillas in Volcanoes National Park in Rwanda and monitored the way the males and infants interacted. The researchers looked at the amount of time the gorillas spent grooming each other and playing, and noted every ten minutes which gorillas were physically close to one another. They also looked at which males were dominant in the group.
“When we think of a human alpha male, we have a very specific set of cultural norms that go along with that, like aggression and not being very paternal,” said Dr. Rosenbaum. “In gorillas, that’s not the case at all; dominant males are often the biggest in the group, but they are gentle and nurturing with the infants.”
There is some degree of research romanticism around gorillas; biology students around the world would consider studying them a career jackpot, and Dr. Rosenbaum agrees:
It’s as cool as it sounds; gorillas are very special animals. I don’t think I appreciated that before I started working with them. I hadn’t set out to study them, but I was fortunate to be offered a place on the project.
The very first day I was in the field, I thought, ‘Wow, it’s amazing to be in the company of these huge, gentle animals.’ They’re very charismatic. It’s hard not to be fascinated by them. You look at them and start to see your own behavior differently, there’s no question about that.
Gorillas are particularly interesting research subjects because of their strong male-infant relationships – they play and groom together – as these are not often seen in mammals. During the field research, Dr. Rosenbaum and her colleagues also collected samples of urine and feces from the gorillas. They are now analyzing those alongside their behavioral data to see if there is a hormonal component to these behaviors.
“We want to understand more about humans’ evolutionary history by watching how gorillas behave. Our goal is to learn more about primate evolution generally, and great apes are particularly interesting since they are humans’ closest living relatives.”
Video: Gorilla Fathers
The researchers filmed male mountain gorillas interacting:
Read the article
This study is freely available until September 16, 2015: S. Rosenbaum et al: “Male rank, not paternity, predicts male–immature relationships in mountain gorillas, Gorilla beringei beringei,” Animal Behaviour (June 2015)
Animal Behaviour is published by Elsevier for the Association for the Study of Animal Behaviour in collaboration with the Animal Behavior Society. First published in 1953, Animal Behaviour contains critical reviews, original papers, and research articles on all aspects of animal behaviour. Book reviews and books received are also featured. Read more.
The lead author
Dr. Stacy Rosenbaum is a biological anthropologist interested in the evolutionary origins of social behavior. As a National Science Foundation postdoctoral fellow at Chicago’s Lincoln Park Zoo, she studies the behavior and physiology of wild mountain gorillas living in Rwanda. Her current research examines how kinship and hormones influence animals’ social networks. She holds a bachelor’s degree in psychology from the University of Wisconsin-Madison and a PhD in anthropology from UCLA.
Stacy is very interested in science education and outreach, with a particular focus on the value of studying behavior, and how everyone can contribute to the conservation of endangered species and habitats.
Elsevier Connect Contributor
After a few accidents, Lucy Goodchild van Hilten discovered that she’s a much better writer than a scientist. Following an MSc in the History of Science, Medicine and Technology at Imperial College London, she became Assistant Editor of Microbiology Today. A stint in the press office at Imperial saw her stories on the front pages, and she moved to Amsterdam to work at Elsevier as Senior Marketing Communications Manager for Life Sciences.