Relationship Between Domestication and Human Social Skills

Brian Hare wants to know why humans are such big babies.  

Well,  that was just the provocative title for his Center for Cognitive Neuroscience talk on Oct. 2. What he wants to know is what happens in the development of human babies that socially advances and separates them from their animal counterparts.


Hare, an associate professor of evolutionary anthropology, discussed human evolution and comparisons to our ancestors and chimpanzees, bonobos and even dogs. He explained that the idea of comparing humans to other species suggests that “something very fundamental happened during human evolution that makes us human– a shift in human development.”

First Hare attempted to evaluate whether certain advanced capabilities of humans are present in other species. One means of doing this was by examining if other species think about the thoughts of others. In a video from an experiment  “Gaze” that Hare conducted, he looks at a chimpanzee named Dorene, and then suddenly glances upwards. The chimp follows suit, gazing up at the ceiling to see what Hare is looking at. From this behavior, Hare inferred that chimpanzees are in fact capable of thinking about the thoughts of others, like the human species.

This led Hare to examine another behavior that is advanced in humans: cooperation. Hare explained that in previous laboratory research, chimpanzees were found to be incredibly uncooperative. Hare’s studies in the field, however, proved the opposite. In an experiment with Alicia Melis and Michael Tomasello, two chimps were put in adjacent, but separate rooms. A treat was visible with a string leading to each chimpanzee. If one animal pulled the string, it just got the string. But if both pulled cooperatively, they ended up with the food. The researchers found that 95% of the chimps could work together to solve this problem to get an equal payoff for both of them. Hare did note, however, that if the chimps had communicated, they could have solved the problem more efficiently.

This showed that where chimpanzees might differ from the human species is in their inability integrate cooperation and communication. With children, Hare explains, this is a fundamental part of development that is established early in life. Because of this, Hare wondered if there is something motivationally different about the structure of cooperation between humans and other species, something that also shows early in development.

When humans work together, Hare said, they understand they have a shared goal and will adjust to different roles to complete the task. This has led to, from an evolutionary perspective, a very “strange” behavior in humans, in which they do things together simply because they like to. Hare calls this “we psychology.” Hare showed two videos side by side: one of his son rolling a ball to his mother, Vanessa Woods, and another of a chimp in a cage rolling a ball with Woods. When Woods stopped playing the game, the chimp reached out of the cage and grabbed her arm and pushed the ball so it would roll back to him. From this, Hare inferred that, like humans, chimps may also have a small tendency for “we psychology.”

In another study, Hare compares two-year-old children to adult and juvenile chimpanzees. In terms of physical cognition, the species were very similar to one another. On the social problem solving front, however, human children were already outperforming juvenile and adult chimpanzees. This study, along with the culmination of his earlier research, reinforced Hare’s idea that something very fundamental happens early in human development that differentiates human’s social and communicative capabilities from other species: domestication.  

“It’s not just that kids are solving problems better, but it may even be that the way kids cognitively organize has changed,” he said.

Hare explains that just knowing the cause to be domestication was not enough, however. He wanted to understand how this worked. Hare referenced extensive breeding research conducted by Dmitri Konstantinovich Belyaev, in which he studied the domestication of the fox. Not only did these foxes show behavioral changes due to domestication, they also displayed morphological and physiological changes: floppy ears, curly tails and high levels of serotonin. Belyaev also found that, like humans, foxes use gestures and communicative cues. So, Hare concluded that the process of domestication influences a realm of social and biological characteristics and could be manipulated and interpreted in many different ways, especially in our own development.


“This doesn’t just happen as a result of artificial selection, or human selection. It can happen as a result of natural selection,” Hare said. “So then we turn to our own species and start looking at whether there’s any evidence in our own evolution for this.” he said.


By Madeline Halpert, Class of 2019

Fisticuffs Among the Mantis Shrimp

When mantis shrimp (Stomatopoda) dispute territory or mating rights, they use the tools at hand – namely two super-sonic bludgeons powerful enough to dismember a live crab or break through a clam shell.

Mantis shrimp are pugnacious pugilistic crustaceans . (Photo by Nazir Amin via Wikimedia Commons.)

Mantis shrimp are pugnacious and pugilistic. (Photo by Nazir Amin via Wikimedia Commons.)

Fortunately, they’ve developed a way to use these deadly clubs on each other without causing too many fatalities. In a ritualized battle called “telson sparring,” the combatants take turns hammering on each other’s tail-plate, which is raised up like a shield.

Graduate student Patrick Green watched more than 30 such contests in captive Panamanian mantis shrimp to discover that it wasn’t the shrimp who hit hardest who won the bout, but the one who hit the most frequently.

Green and his Ph.D. supervisor, biology professor Sheila Patek, hypothesize that the ritualized fighting could be a display of overall vigor and tenacity rather than outright punching power.

CITATION: “Contests with deadly weapons: telson sparring in mantis shrimp (Stomatopoda),” Green PA, Patek SN. Biology Letters, Sept. 2015. DOI:10.1098/rsbl.2015.0558

Karl Leif Bates

Post by Karl Leif Bates, Director of Research Communications

Four-Fifths of a Banana is Better than Half

Fractions strike fear in the hearts of many grade schoolers – but a new study reveals that they don’t pose a problem for monkeys.

Even as adults, many of us struggle to compute tips, work out our taxes, or perform a slew of other tasks that use proportions or percentages. Where did our teachers and parents go wrong when explaining discounts and portions of pie? Are our brains simply not built to handle quantitative part-whole relationships?

Lauren Brent macaques

Fractions and logical relationships are some of the things a wild macaque might think about while grooming and being groomed. (image copyright Lauren Brent)

To try to answer these questions, my colleagues and I wanted to test whether other species understand fractions. If our fellow primates can reason about proportions, our minds likely evolved to do so too.

In our study, which appears online in the journal Animal Cognition, Marley Rossa (Trinity 2014), Dr. Elizabeth Brannon, and I asked whether rhesus monkeys (Macaca mulatta) are able to compare ratios.

We let the monkeys play on a touch-screen computer for a candy reward. First we trained them to distinguish between two shapes that appeared on the screen: a black circle and a white diamond. When they touched the black circle, they heard a ding sound and received a piece of candy. But when they touched the white diamond, they heard a buzz sound and did not get any candy. The candy-loving monkeys quickly developed a habit of choosing the rewarding black circle.

Fractions example taken from

Next we introduced fractions. We showed two arrays on the screen, each with several black circles and white diamonds. The monkeys’ job was to touch the array having a greater ratio of black circles to white diamonds. For example, if there were three black circles and nine white diamonds on the left, and eight black circles and five white diamonds on the right, the monkey needed to touch the right side of the screen to earn her candy (8:5 is better than 3:9).

We didn’t always make it so easy, though. Sometimes both arrays had more black circles than white diamonds, or vice versa. Sometimes the array with the higher black-circle-to-white-diamond ratio actually had fewer black circles overall. They needed to find the largest fraction of black circles. For example, if there were eight black circles and 16 white diamonds on the left (8:16), and five black circles and six white diamonds on the right (5:6), the correct answer would be the latter, even though there were more black circles on the left side. That is how we made sure that monkeys were paying attention to the relative numbers of shapes in both arrays.

The monkeys were able to learn to compare proportions. They chose the array with the higher black-circle-to-white-diamond ratio about three-quarters of the time. Impressively, when we showed them new arrays with number combinations they had never seen before, the monkeys still tended to select the array with the better ratio.

Our results suggest that monkeys understand the magnitude of ratios. They also indicate that monkeys might be able to answer another type of question: analogies. These four-part statements you may have seen on standardized tests take the form “glove is to hand as sock is to foot.”

This kind of reasoning requires not only recognizing the relationship between two items (glove and hand) but also how that relationship compares with the relationship between the other two items (sock and foot). Understanding the relationships between relationships — that is, second-order relationships — was believed to require language, making it possibly a uniquely human ability. But in our study, monkeys successfully determined the relationship between two fractions – each one a relationship between two numbers – to make their choices.

If monkeys can reason about ratios and maybe even analogies, our minds are likely to have been set up with these skills as well.

The next step for this line of research will be to figure out how best to employ these in-born abilities when teaching proportions, percentages, and fractions to human children.

CITATION: “Comparison of discrete ratios by rhesus macaques (Macaca mulatta)” Caroline B. Drucker, Marley A. Rossa, Elizabeth M. Brannon. Animal Cognition, Aug. 19, 2015. DOI: 10.1007/s10071-015-0914-9


Guest post by graduate student Caroline B. Drucker. Caroline is curious about both the evolutionary origins and neural basis of numerical cognition, which she currently studies in lemurs and rhesus monkeys.

Uneasy Lies the Gut That Wears the Crown

Meerkats of the Kalahari Desert are social, and wormy. (all photos by Ed Kabay)

Meerkats of the Kalahari Desert are social, and wormy. (Photo by Ed Kabay)


The dominant matriarchs of meerkat society carry a heavy burden.

Not only are these females stressed from having to constantly scold and cajole the rowdy members of the tribe to maintain their perch as the primary breeders and enforcers of the clan, they apparently host more parasites as well.

In a two-year study at the Kuruman River Reserve in South Africa’s Kalahari Desert, Duke graduate student Kendra Smyth sampled the parasite diversity of 83 sexually mature meerkats living in 18 social groups.

Specifically, she gathered 97 freshly deposited poops for later analysis. Such is the glamour of graduate student field work.

After diluting and spinning, the samples were microscopically analyzed for careful counting of the eggs of six species of intestinal worms.

What Smyth found in the end was consistent with similar studies done in male-dominant societies: The boss is more heavily parasitized.

So, why is that? Well, it might be that the matriarch’s stressful job takes some resources away from her immune defenses, or it may be that her close contact with more members of the tribe puts her at greater risk of picking up worms from others.

Meerkats, and graduate students like Kendra Smyth, are often seen scanning the horizon.

Meerkats, and graduate students like Kendra Smyth, are often seen scanning the horizon. (Photo by Ed Kabay)

The bottom line is that the meerkat model of sexual selection carries a cost, which, as in other species, is more heavily borne by the breeders.

Smyth’s findings appeared online this month in Behavioral Ecology and are a part of her dissertation research on immune function in meerkats. In addition to poop, she’s sampling blood and looking at hormone levels and other variables.

“Parasites are a proxy for measuring the immune system,” said Smyth, who is a fourth-year grad student with Christine Drea of Evolutionary Anthropology and the Program in Ecology.

And wild-living meerkats can be a kind of proxy for humans. “Most of what we know about the immune system comes from laboratory mice living in unrealistic conditions,” Smyth said. “They’re housed singly in clean cages and they’re parasite-free. I’m not convinced that that’s how the immune system works when you put them in the natural world.”

“For any kind of species living in groups, like humans, it’s important to understand the dynamics of the spread of disease and which individuals might be susceptible,” she said.

During one meerkat weigh-in, this practical joker put his thumb on the scale.

During one meerkat weigh-in, this practical joker put his thumb on the scale. (Photo by Kendra Smyth)

This work was supported by the National Science Foundation (IOS-1021633) and a dissertation travel grant from the Duke Graduate School. Research at the Kuruman River Reserve is supported by the European Research Council (294494), Cambridge, Duke and Zurich Universities.

Post by Karl Leif Bates

Karl Leif Bates

Marine Lab Hosts 500+ at Open House

In what was a record high turnout, more than 500 people made their way to Pivers Island on Saturday Aug. 1, for the Duke University Marine Lab’s annual open house. Visitors listened to whales, peered at plankton and sea urchin larvae through microscopes, and learned how salinity gradients and wind can drive ocean currents at 16 research stations scattered throughout the campus. Kids of all ages also got to meet horse conchs, pen shell clams, tulip snails, fiddler crabs, slipper snails and other creatures in the marine lab’s touch tanks. “We don’t think of snails as having teeth but they really do; that radula is quite a weapon. It’s like a cross between a chainsaw and a tongue,” said Duke visiting professor Jim Welch. Photos by Amy Chapman-Braun, Nicholas School of the Environment at Duke.

Is it Just Us?

Plankzooka, on the left there, is two big tubes strapped on either side of the autonomous undersea rover Sentry.

Plankzooka, on the left there, is two big tubes strapped on either side of the autonomous undersea rover Sentry.

We certainly admired the news Friday coming out of a marine science cruise that hasn’t even ended: They found a shipwreck a mile down while also pioneering a new device for gently and precisely sampling plankton at those crushing and dark depths.

But we couldn’t help but notice the “plankzooka’s” uncanny resemblance to a familiar cartoon character.  Here’s an example of some of the juvenile plankton it collected around a methane seep on the sea floor.


A sampling of juvenile plankton from the deep sea.