Boys & Girls

Ask, May/Jun 2008 by Koppel, Aaron

in the Primate World

Boys will be boys. Girls will be girls. Sounds familiar, sure, but what exactly does it mean? Sometimes it helps to look at other animals for answers.

Think about your closest relatives. No, not your brothers and sisters, but your relatives in the animal kingdom-monkeys and apes. We all belong to the primate family, and we can learn a lot from our monkey and ape relatives.

Male and female primates are equally important to their communities. So why do they look and act so differently? The differences between the sexes give them each advantages that make it easier for them to live longer, have more healthy babies, and make sure their species survive.

Who's a Tough Guy?

Among most monkeys and apes, males are just plain bigger than females. Take the olive baboons of Africa: a male weighs about 20 pounds more than a female. Doesn't sound like a lot, but at about 53 pounds, he's almost twice as heavy as she is.

The same holds true for western lowland gorillas. Males weigh 400 pounds while females weigh 200. Males generally grow over five feet tall, while females top off closer to four feet. Imagine how much stronger the male is. He dominates the group with his overwhelming strength, which he shows off by beating his chest with his fists.

The strength of the orangutan is legendary. The orang is the largest ape that lives in the trees, and both sexes need great strength to propel their bodies from branch to branch. Female orangutans are more than three times as strong as female humans, and male orangutans, about twice as large as females, are more than four times as strong as male humans. Male orangs are so big that they spend most of their time on the ground because tree branches simply won't hold their weight for long. On Borneo, one of two Southeast Asian islands where the big orange apes live, a native chief once suggested that a male orangutan could kill a crocodile with his bare hands.

Act Your Size!

Sure, male primates are bigger than females. But what does size have to do with behavior? Let's say a couple of male olive baboons brawl with each other over a female, who watches them from the sidelines. If a male is bigger and stronger than his competitor, then he is likely to win the fight-and the mate. So it's good to be tougher than the next guy, because the strongest male gets to pass down his genes and traits to the next generation.

A growing western lowland gorilla male uses his size and strength to fight off other males. He banishes them from living in his group. This means he can mate with all the females, who are happy to stick with him because of his ability to protect them and their babies. His brawn helps him organize his group. Later in life, when he loses his top-notch position to an up-and-coming youngster, he leaves the group and goes off on his own.

Pretty... and Pretty Loud

But size and strength aren't the only differences between males and females. Some male primates are different right down to the color of their skin. The most colorful primate of all is the mandrill. At least, male mandrills are colorful. Females' snouts look drab compared with the vivid reds and blues of the males'. Why the difference? Brighter colors make male mandrills more attractive to females.

While male mandrills are pretty, other primates are pretty loud. Think of loud mammals: tigers, wolves, elephants. Surprisingly, blue whales are the loudest mammals of all, but the red howler monkeys of South America come in a close second. The males make tremendous howling "dawn choruses" that can be heard more than three miles away. The females join in, but their howls are not as loud. Male howler monkeys aren't that much bigger than females, but they do have an enlarged hyoid, a bone on the tongue that acts like a loudspeaker, and a big larynx, an organ in the neck that works as a sound chamber.

Some researchers believe that the dawn chorus allows troops to keep a safe distance from one another, so that they won't waste their energy fighting over food. Mature leaves, a plentiful but not very energy-rich food, make up most of the monkeys' diet. If a troop gets lucky, it may find fruit, flowers, and young leaves, all of which are more nutritious than mature leaves. The ruckus that the male howlers make sends the message: Keep Out!

By securing a big section of forest, males increase the likelihood of everyone in their troop finding a good breakfast. This is especially important for females, who need extra energy to successfully have babies and raise them.

Family Time

Indeed, while males may be bigger, stronger, louder, and fancier, females have one of the most important jobs in primate society: reproduction. Unborn young develop in their mothers' wombs, weighing them down for a long period of time. An orangutan's pregnancy lasts eight months. Even the smallest of monkeys, the pygmy marmoset, carries her young for five months. Then she delivers not one but two babies: twins.

However, birth is only the first step. The young must survive to adulthood. In the world of primates, this means that a baby must be nourished and cared for. The mother almost always does this work. She nurses her babies with energy-rich milk and carries them around while they grow strong and independent. An olive baboon mother carries her baby around with her for at least eight months. A mother orangutan lugs her baby around on her belly and back for two and a half years!