Chapter 2 - 6

06 Zoology

Listen to a lecture in a zoology class. Fill in the diagram with the information that you hear.

M: OK everyone, listen up. We’re going to conclude this week’s lecture series by talking about two apes that are very similar to one another. I’m talking about our close cousins, gorillas and chimpanzees.

I’m sure most of you recognize that outside of their respective sizes, gorillas and chimpanzees are very similar physically, but what about socially? In fact, there are some notable differences in the social structure of these two primates that I would like to spend some time going over.

First, let’s talk about similarities. You should note that gorillas and chimpanzees share almost the exact same DNA as humans. Gorillas and humans share approximately ninety-seven to ninety-eight percent of the same DNA, while chimpanzees and humans have approximately ninety-eight to ninty-nine percent in common.

Evolutionally, this not only makes gorillas and chimps closely related to us, but to each other as well. So obviously, they’re going to share lots of similar characteristics, right?

For example, both gorillas and chimps walk on their knuckles and tend to form groups.

Each of these groups consists of a dominant male that acts as the group leader. But here we start to run into some differences in group structure that work to differentiate the two primates.

You see, gorillas are much more solitary than chimpanzees. Yes, they do form groups, but these gorilla groups are much smaller than chimpanzee groups. A gorilla group usually consists of about a dozen individuals: a male gorilla, several adult females, and their young.

Sometimes the group may include a few younger males, but they rarely mate with any of the females. The females belong to the dominant male.

Chimps, on the other hand, live in large groups of 50 or more individuals, sort of like a mini-society.

And unlike gorillas, many chimps in the group may be male. This large group consists of several smaller subgroups−another characteristic that is not seen with gorillas.

These chimpanzees subgroups often consist of a mother and siblings. Much of the younger chimp’s behavior is learned from the different individuals in their subgroups and, like humans, chimps appear to have a special bond with their mothers and siblings.

Now, as in the case of many social animals, the dominant males in both gorilla and chimpanzee groups are usually the biggest in size and brute strength. This is not to say that the dominant male will stay in power forever.

Both gorillas and chimps can be, and often are, overthrown by others. Dominant male gorillas can be overthrown by a stronger, tougher gorilla, who will then take over the group.

The displaced gorilla will then usually spend the rest of his life alone by himself. Then what about chimps? Well chimpanzees display similar dominance patterns, although displaced males are not always sent into isolation like displaced gorilla males.

There is one exception to this system of dominance that I feel is worth mentioning. Whereas gorillas rely on brute strength to gain the dominance of a group, it appears that chimps may also rely on intelligence to move up their group hierarchy.

In a study conducted by primatologist Jane Goodall in 1964, a chimp named ”Mike” was able to gain control of a group because he was smart.

This chimp was not the usual candidate for a leader. He was one of the lowest in the dominance hierarchy and very weak physically.

He was often attacked by chimps much bigger than him. But one day, Mike stumbled across a kerosene can lying around Goodall’s camp. None of the other champs had paid any attention to them, except for Mike.

Grabbing one of the kerosene cans, Mike began charging the other males of the group and banging the can with his fists. All the other chimps were terrified of the loud noise, and Mike became the leader of the group without even fighting.

He proved that chimps can use their intelligence, and not just brute strength, to gain power.

So what do these differences in social structure tell us about these animals? Perhaps it demonstrates the slightly closer genetic relationship that chimps have with humans.

Large communities, subgroups, gaining power through intelligence−are all unique characteristics that humans and chimpanzees share.

Whatever the case, these slight differences in the social structure of gorillas and chimpanzees are fascinating topics for further study.

1) According to the professor, in which aspect do chimps and gorillas differ most?

2) What is a similarity that chimps and gorillas share?

3) What does the professor say that Mike used to gain dominance of the group?