Sunday, December 28, 2014

It's a stressful job being the alpha male baboon

Julius Caesar is said to have thought it was much better to be the alpha male of a small village in Gaul than the beta male of Rome. Until recently, scientists thought alpha males were indeed in the most desirable position all around - less stress, more sex, better food. What's not to like?

It’s a stressful job being the alpha male baboon

Tony Auth / The Philadelphia Inquirer (tauth@phillynews.com)
Tony Auth / The Philadelphia Inquirer (tauth@phillynews.com)

Julius Caesar is said to have thought it was much better to be the alpha male of a small village in Gaul than the beta male of Rome. Until recently, scientists thought alpha males were indeed in the most desirable position all around - less stress, more sex, better food. What's not to like?

After following 125 male baboons for nine years in the wilds of Kenya, a team led by Princeton University researchers found that the alpha males excreted more stress hormones on average than males below them on the totem pole. "It makes sense that the highest-ranking male would be more stressed," said Craig Packer, a biologist from the University of Minnesota, who has studied social rankings in baboons and lions.

"You've got to look over your shoulder, while the subordinates can just go off into the bushes and chill," he said.

And look at what happened to Julius Caesar.

Many biologists are fascinated by social hierarchies because they exist in many species, and an animal's position often has profound physiological consequences.

Becoming alpha male often raises testosterone, said anthropologist Joanna Setchell of Durham University in England. In African baboons called mandrills, this causes a male's face to become brightly colored, she said. Females find this irresistible.

In a paper describing these new baboon findings, published last week in Science, the researchers hint that their findings speak to the human condition. And several studies have shown that people of lower socioeconomic status have higher levels of the stress hormone cortisol.

But are human groups really analogous to a baboon hierarchy?

Dominance is a physical contest for baboons, played out among the young and strong, said Packer. "We're not talking about [media mogul] Rupert Murdoch." In the baboon world he'd have been ousted long ago.

The same goes for Italy's septuagenarian prime minister Silvio Berlusconi, accused of cavorting with a teenage belly dancer at one of his so-called bunga bunga parties.

"If he were a baboon, he wouldn't be doing any bunga bunga," Packer said.

Being alpha male is more important for baboons than it is for many other species, said Packer, because the top-ranking male has almost all the sex. "Being dominant is what being a male is all about. . . . This is their one chance to get genes into the next generation."

In most human groups, it's pretty hard for one guy to monopolize all the females. The reason it's possible in baboons, said University of Pennsylvania psychology professor Robert Seyfarth, is that females are only desirable to males during the fertile part of their reproductive cycles, when their rear ends swell and turn a conspicuous shade of pink.

That means that most of the time there's only one fertile female in any troop, or occasionally two, giving the second-ranking male a chance.

Seyfarth, who also studies baboons in the wild, said this new paper builds on earlier studies by Stanford University professor Robert Sapolsky, who discovered that alpha males were less stressed than everyone else at times when the baboon hierarchy was relatively stable, but more stressed than subordinates when it was in flux.

This new study was bigger, said Seyfarth, and the team used a different method for measuring stress hormones.

In the past, scientists had to capture the baboons and measure their stress hormones by taking blood, but that was problematic, said Seyfarth. "There was no way of measuring stress without causing stress."

Sapolsky tried to correct for this by taking multiple samples over time and recording how fast the level of stress hormones went down. The Princeton-led team went for a more noninvasive method. They followed the baboons around with paper cups and collected their droppings, from which stress hormones could be assessed.

A typical baboon group has 30 to 100 individuals, said Princeton's Jeanne Altmann, one of the authors on the paper. Since males mature more slowly and also die earlier, there are usually 3 to 15 adult males per group. Whatever the number, she said, they fight to form a linear hierarchy from top to bottom.

She and her colleagues found the highest stress hormone levels concentrated at the top and bottom of the pecking order. The least stressed were the second-ranked "beta males."

It's also stressful to be king among chimpanzees, said Martin Muller, an anthropologist from the University of New Mexico, who showed in 2004 that the highest-ranking chimps had higher levels of stress hormones than their subordinates.

He suspects in both species, this reflects physical rather than psychological stress. It's hard work to be the alpha chimp, he said. You have to guard your position against other males, and try to keep the females from mating with your rivals, as female chimps are wont to do.

Female baboons also have a social ranking they're born into, based on the rank of their mothers, said Durham's Setchell. They just accept this, rather than fight to change it.

What constitutes status, and what it means, varies from one species to another. Status matters to us, but unlike baboons, humans have many ways of attracting the opposite sex - power is just one avenue, along with looks, humor, artistic flair, or the desire to care for children.

The one lesson that applies across species is the idea that evolution doesn't necessarily lead to one ideal personality type, even in animals.

Evolution, said Penn's Seyfarth, can allow many types to thrive - the aggressive and the shy, the pushy and the laid-back. That's why we see so many types of people.

About this blog
Faye Flam - writer
In pursuit of her stories, writer Faye Flam has weathered storms in Greenland, gotten frost nip at the South Pole, and floated weightless aboard NASA’s zero-g plane. She has a degree in geophysics from the California Institute of Technology and started her writing career with the Economist. She later took on the particle physics and cosmology beat at Science Magazine before coming to the Inquirer in 1995. Her previous science column, “Carnal Knowledge,” ran from 2005 to 2008. Her new column and blog, Planet of the Apes, explores the topic of evolution and runs here and in the Inquirer’s health section each Monday. Email Faye at fflam@phillynews.com. Reach Planet of the at fflam@phillynews.com.

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