Evolution And History

92 CHAPTER 4 | Primate Behavior

zoo of Madrid, Spain. It began

when a 5-year-old female

rubbed apples against a

sharp corner of a concrete

wall in order to lick the

mashed pieces and juice

left on the wall. From this

youngster, the practice

of “smearing” spread to

her peers, and within five

years most group mem-

bers were performing the

operation frequently and

consistently. The innova-

tion has become standard-

ized and durable, having

transcended two generations in the group.^22

Another dramatic example of learning is afforded by

the way chimpanzees in West Africa crack open oil-palm

nuts. For this they use tools: an anvil stone with a level

surface on which to place the nut and a good-sized ham-

mer stone to crack it. Not any stone will do; it must be of

the right shape and weight, and the anvil may require lev-

eling by placing smaller stones beneath one or more edges.

Nor does random banging away do the job; the nut has to

be hit at the right speed and the right trajectory, or else the

nut simply flies off into the forest. Last but not least, the

apes must avoid mashing their fingers, rather than the nut.

According to fieldworkers, the expertise of the chimps far

exceeds that of any human who tries cracking these hard-

est nuts in the world.

Youngsters learn this process by staying near to adults

who are cracking nuts, where their mothers share some

of the food. This teaches them about the edibility of the

nuts but not how to get at what is edible. This they learn

by observing and by “aping” (copying) the adults. At first

they play with a nut or stone alone; later they begin to ran-

domly combine objects. They soon learn, however, that

placing nuts on anvils and hitting them with a hand or

foot gets them nowhere.

Only after three years of futile effort do they begin to

coordinate all of the multiple actions and objects, but even

then it is only after a great deal of practice, by the age of

6 or 7 years, that they become proficient in this task. They

do this for over a thousand days. Evidently, it is social mo-

tivation that accounts for their perseverance after at least

three years of failure, with no reward to reinforce their ef-

fort. At first, they are motivated by a desire to act like the

In the 1950s and early 1960s, one particularly bright

young female macaque named Imo (Japanese primatolo-

gists always considered it appropriate to name individual

animals) started several innovative behaviors in her troop.

She figured out that grain could be separated from sand if

it was placed in water. The sand sank and the grain floated

clean, making it much easier to eat. She also began the

practice of washing the sweet potatoes that primatologists

provided—first in fresh water but later in the ocean, pre-

sumably because of the pleasant taste the saltwater added.

In each case, these innovations were initially imitated by

other young animals; Imo’s mother was the lone older ma-

caque to embrace the innovations right away.

One newly discovered example is a technique of food

manipulation on the part of captive chimpanzees in the

In the same way that young Imo got her troop to begin washing

sweet potatoes in saltwater, at Kyoto University’s Koshima Island

Primatology Research Preserve another young female macaque

recently taught other macaques to bathe in hot springs. In the

Nagano Mountains of Japan, this macaque, named Mukbili, began

bathing in the springs. Others followed her, and now this is an

activity practiced by all members of the group.

© age fotostock/SuperStock

Pacific

Ocean

Philippine

Sea

East

China

Sea

Sea of

Japan

Nagano

Tokyo

JAPAN

CHINA RUSSIA

NORTH

VIETNAM

SOUTH

VIETNAM

Koshima

(^22) Fernandez-Carriba, S., & Loeches, A. (2001). Fruit smearing by captive
chimpanzees: A newly observed food-processing behavior. Current Anthro-
pology 42, 143–147.