24“ Sweet-Potato Washing" Revisited

SATOSHI HIRATA! , KUNIO WATANABE! , and MASAO KAWAI 2

1 Introduction
Japanese monkeys (Macaca fuscata) on Koshima Island wash sweet potatoes. This
fact is quite well known, and is often discussed as an aspect of “:culture" in nonhuman animals. However, the full picture is not always entirely understood. The
finding of sweet-potato washing among Koshima monkeys followed theoreticalconsiderations ofculture in nonhuman animals presented by Imanisl泣， andfrom
the beginning research on Japanese monkeys has developed from anthropologicalconcerns about human evolution. In 由is chapter, we would like to illustrate thehistory of sweet-potato washing and other characteristic behaviors shown by
Koshima monkeys (for reviews , see also Itani and Nishimura 1973; Nishida 1987).

2 Prehistory of Sweet-Potato Washing
In 1948, when Kinji Imanishi, Shunzo Kawamura, and Junichiro Itani were conducting research on semiwild horses at Toi Peninsula in Miyazaki Prefecture, Japan, they happened to find a group ofwild Japanese monkeys. This was the start ofmany studies of wild Japanese monkeys. Two points characterized these studies.
The first is that they are a long-term research project which still continues after
more than a half a century. The second is the individual identification of the monkeys. Each monkey was given a nickname , and not labeled like a rat or mouse in alaboratory. The researchers began to understand the cognition,behavior, and society of Japanese monkeys in the wild through long-term research with individual
identification.
In November 1948, soon after their encounter with the wild Japanese monkeys
at Toi Peninsula, Imanishi, Ita剖， and Kawamura visited Koshima Island in thesame prefecture for the first time (Fig.l). Koshima was the first , and that time theonly, monkey habitat designated a natural monument in Japan. Intensive study ofthe Koshima troop of Japanese monkeys started since then with the success of1
2

Primate Research Institute, Kyoto University, 41 Kanr 泊， Inuyama, Aichi 484-8506, Japan
Museum of Nature and Human Activities, 6 Yayoigaoka, Sanda, Hyogo 669-1546, Japan
487

488

S. Hirata et al.

Fig.l. Koshima Island (center)

provisioning in 1952 (see Chapter 20 byWatanabe, this volume). These workers
and their colleagues also began to focus their research on monkeys at several othersites in Japan. These included Takasakiyama in 1950 by Kawamura and Ital祉， Minooin 1950 by Kawamura , Arashiyama in 1952 by Kawamura and Ita剖， Yakushima in
1952 by Kawamura and Ita剖， Shimokita in 1952 by !tal祉， Kinkazan in 1959 by
Yoshiba, and Jigokudani in 1960 by Azuma, Sugiyama, and Wada.
In the meantime, in 1952, Imanishi published a landmark paper entitled “ Theevolution of human nature:' written in Japanese. At the very beginning of theresearch on Japanese monkeys, or even before that, Imanishi's mind was oriented
toward anthropology. The paper is rather an imaginary theoretical one, as only alittle was known about nonhuman primates at 出at time. The paper takes the formof fantasy, with some imaginary characters debating on several subjects. It goes asfollows:
Evolutionist “ First of all,I think it's good to start with a commonplace topic. Well, people sa弘animals live only by instinct, while humans have culture:'
Layman “ To be a human means to have a culture:'
Evolutionist “. .. Instinct is inherited through a genetic channel, while culture is transmitted
through a nongenetic channel. Culture is acquired through learning and teaching, so that themodel and the pedagogy are necessary. Therefore, a group life is inevitably required for theestablishment of a culture. Thus, to maintain a culture as culture, the group life must be aperpetual one."
Layman “If the condition for the establishment of a culture is just like you described, thenculture may be seen not only in humans but also in other animals that live in a perpetualsocial group. How is it in monkeys? Do you have culture, Monkey?"
Monkey “ We live in a perpetual social group... but it is not made clear yet how much of our
behavior is determined by instinct and how much is determined by culture..."In the subsequent discussion ,Imanishi let Monkey say “a change in food habits
can be considered as a change in culture:' and Evolutionist say “ when an experience of an individual is transmitted to 出e next generation, it is called a culture:'
The above hypothesis by Imanishi was later corroborated by colleagues in thefield. The first discussion about the culture ofJ apanese monkeys that had a basis in
actual field observations was proposed by Kawamura in “On a new type of feeding24 “ Sweet-Potato Washing" Revisited489

habit which developed in a group of wild Japanese monkeys" (1954) , a paper
written in Japanese. Kawamura later publi誌shed three related papers: “Pr昀ehuman
C叫tωure"叮，(1956) ,"The process ofsubculture propagation among Japanese macaques"(1959) , and “Subculture in Japanese monkeys" (1965); the first and third were
written in Japanese, and the second in English. In these papers , Kawamura gave
examples ofpossible cultur叫 behavior in Japanese monkeys, such as the repertoire
offoods (e.g. , monkeys in some troops eat bird eggs, while monkeys in other troops
do not) , the nomadism of the troop (i. e. , the maintenance of a home range by agroup , and also the moving pattern within the home range, which is inherited overgenerations) , social behavior (e~g.， many adult males of one troop show paternalcare towards infants, while males in other troops do not) , and social structure (e.g. ,males are tolerant ofeach other in some troops, while males in other troops becomemuch more aggressive when approached by other members). Kawamura attempted
to probe the cultural behavior of monkeys by checking on the variability of the
behavior across troops. He said that: “ The life ofhigher animals closer to humans
are in the mist at present. We should not dispose of the question by considering
whether or not they have laI!guage or productions, but we must keep our outlook
broad and explore untouched areas to shed light on the buried evolutionary path"(Kawamura 1965); “Our purpose ~s not to go into an endless argument about thedefinition ofthe term, but to conduct concrete research about in what way a simple
behavioral mechanism has developed into a higher complex one in animals. ...,
isn't it possible to cast a completely different light on human culture by carefully
tracing each step and by arriving at the evolutionary perspective?" (Kawamura 1956).
The first of the four above-mentioned papers by Kawamura was the first reporton the sweet-potato washing behavior of Koshima monkeys. He briefly described
the invention of sweet-potato washing by a 1.5-year-old female and its propagation to three other members by 1954. Later, Kawamura, Kawai,and colleagues conducted a follow-up study of this behavior, and Kawai (1965) wrote about the process of propagation in detail, along with reports of three other newly acquired
behaviors. This paper is an extremely detailed record ofthese well-kn

3 Revisit to Kawai (1965): “ Newly Acquired Precultural
Behavior of the Natural Troop of Japanese Monkeys on
Koshima Islet"
Before going to the paper itself, one may wonder why Kawai used a coined word
“preculture." Let us first give an explanation (Kawai 1964). Imagine the following
example: Japanese people eat sea cucumbe的 but people in Western countries donot. Such a phenomenon can be labeled the (‘:culture" of food. Culture can be loosely
defined as a mode oflife that is invented in a group , shar叫 by group members, andtransmitted to subsequent generations through social media. However, when we
say “:culture:' its substances and levels are, of course, different in monkeys and

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S. Hirata et al.

humans. The word “culture" often reminds us of literature, art, music, pictures,
academe , religion, etc. It cannot be denied that there is a big gap between humanculture and monkey culture. In the case ofmonkeys , they do not have the ability toteach something. The way infant monkeys acquire a behavior is that they somehow
become familiar with a certain behavior while being with their mothers, and acquire it in some way. In the case ofhumans, those who do not follow the culture of
their own community will be treated as unorthodox and will be socially punished;human culture has the power to restrict or constrain the behavior of a person who
belongs to that socie你 Thus， human culture of any kind is systematized in some
wa手 On the other hand, a monkey who does not follow a culture will not be blamed,and no social restriction works against a violation. We must not overestimate thesituation and say that “ monkeys have culture:' and then confuse it with humanculture. Cultural behavior in monkeys must always be discussed in the light ofevolution. This is the reason why the term "preculture:' which takes such differences into consideration, was used in Kawai's paper. An abridged edition of thepaper follows.

3.1 Sweet-Potato Washing (SPW) Behavior
3.1.1 Acquisition of SPW Behavior
Sweet-potato washing (SPW) is a behavior in which monkeys take a sweet potato
to the edge of the water and wash the sand off the potato with water (Fig. 2). Thisbehavior was begun in September 1953 by a female named Imo , who was one anda halfyears old at that time.
This behavior gradually spread to other monkeys. Table 1 shows the process of
propagation during the period from 1953 to March 1958. In 1958, the acquisition
rate in adults was 18.10/0: i. e. , 2 out of 11 animals (6 males and 5 females). The rate
in monkeys aged between 2 and 7 years was 78.90/0: i. e. , 15 out of 19 (10 males and9 females).After that, most newborns began to show this behavior. In August 1962,
36 out of 49 monkeys over 2 years old showed SPW behavior (73.40/0). There were
13 monkeys who did not show SPW behavior. Out of 11 monkeys over 12 years old,i. e. , those born before 1950, only two females showed SPW behavior (Eba andNami). On the other hand, among the monkeys born after 1951 , only 4 individuals
did not perform this behavior. Interestingly, they were all Nami's children.

3.1.2 Process of Propagation
The acquisition of SPW behavior could be divided into two periods: before andafter 1958. The author calls them the first and second period, respectivel手

3. 1.2. 1 The First Period (The Period of Individual Propagation)
This is the period when monkeys born before 1956 acquired SPW behavior. The
times and processes of acquisition were diverse. Adult monkeys who did not acquire the behavior during this period could not acquire it later.
Figure 3 and Table 1 show us the importance of age , sex, and kinship. Most

24 “ Sweet-Potato Washing" Revisited491

Fig. 2. Sweet-potato washing(SPW) behavior

Table 1. The year and age when the monkeys acquired SPW behavior
Age
Year

1- 1. 52-2 .5

1953
1954
1955
1956

Imo ♀

Semushi ♂

1957

Hama ♀，

3

5

6

Adult
Eba ♀

Uni ♂
Ei ♂

Nomi ♂

Kon ♂

Sango ♀，

Jugo ♂

Aome ♀
Harajiro ♀

Enoki ♀

1958

Zabon ♀，
Nogi ♀

Sasa ♀

Nami ♀

S. Hirata et ale

492

Ub.t

Utsubo1949

No吋

Fig.3. The lineages ofthe Koshima troop
and the acquisition of SPW and WPM
behavior as of 1962. Individuals whodied after 1949 are not included. Numerals to the left above the names 恤，dicate 血e year when the monkeys acquired SPW behavior. Numerals to theright above the names indicate 也eyear
when the monkeys acquired WPM behavior (snatching behavior is not included)戶ι一、戶~(Gosuke) I
1951-2叫mI﹒ (~on) I
•5~~i

19閱

I

1952

。 51111

.Aome

55

1953

.(Nom j)

1954
。 159

1955

.Nogi
057182

1956

I

I; Hama

I

I

0

I

111

; Zabon

。， 59

1957

• Nofl叫i

1958

.Hamo
。 161

1959

.Zai

1960

• Hasu• Nobori

1961
1962

Masu

Hata

Bora

Zari

"Noro

Males born before 1949: Kamina肘， Akakin. Mobo , Hiyoshimaru. (Hanakake).: SPW monkey
0: WPM monkey( ): Solitary monkey
t: Died
57

53

.Nami

• Eba

loot

,

i

I

I

Natsu

1949
1950

-53

.(Ita)

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.Imo

Naki

。 58

1

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58

• (Jugo)

1953
55

1954

.(E j)。 5859eu e-a

1961

Iruka

SakakiSatsukiFash--nu

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1955
m-enHURSRHehMU
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fnilIlli---SE
2UF:
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h
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• Sasa-Ball--as1HM
Il--aIEll--mlil---Ill-m

Na e

Kisu

Edo

Tsushi1962

competent in acquiring SPW behavior weI吋 uveniles between 1 and 2.5 years old.
Males older than 4 years had great difficulty in acquiring this behavior. Females, on
the other hand, could acquire SPW behavior even if they were older than 4 years,
but judging by the fact that only 2 females out of 11 born before 1950 did acquire
the behavior,old age was obviouslya great obstacle in both sexes for the acquisition
ofthis behavior.
What causes the difference between males and females in the acquisition ofthis
behavior? In order to acquire SPW behavior, a close social interaction with monkeys engaging in it (SPW-monkey) 的 feeding time seemed to play an importantrole. In this lies a difference between males and females which is due to their social
status. When a male becomes 4 years old, he generally begins to move from thecenter to the periphery ofthe troop. Therefore, the social interactions ofadolescentand adult males with females and juveniles in the center ofthe group become very

24 “ Sweet-Potato Washing)) Revisited493

limited, and they seldom feed with females and juveniles. On the other hand, allfemales live closely with each other in the center of the troop. In particular, motherand child often move together. Kawamura (1954 , 1956) suggested the importanceof mother-child relationships in acquiring this behavior by describing a typicalexample of the behavior ofImo and her mother Eba. Eba , the mother of the originator of SPW behavior, acquired it early on although she was an adult female. The
same can be said for the four females who acquired the behavior when they wereolder than 4 years.
The order of acquisition ofthe behavior was the young before the old within thesame family: i. e. ,the child rather than the mother, and the younger brother or sister
rather than the older ones. Kawamura (1954, 1956) pointed out that propagation of
the behavior had two courses: through playmate relations and through kinship.
The propagation in this period was done mostly from child to mother, and fromyounger sibling to older one. As propagation was done through the relationship ofindividuals in the first period, this period was labeled the period of individual
propagatIon.

3. 1.2.2 The Second Period (The Period of Precultural Propagation)
After 1959, some aspects of propagation were different from those of the first period. SPW behavior was no longer a new behavior to the troop; it had been fIXed in
the troop during 1958-1959. Monkeys born during this period accepted SPW
behavior as a normal feeding behavior and learned it without any resistance.
Sweet potato skins fall to the bottom of the water while SPW團monkeys are eating.
This means that babies have the experience ofeating their potatoes in water at the
beginning of the development of their feeding behavior. The babies are always
with their mothers, and they stare at their mother while she is doing SPW behavior.
In this manner infants acquire SPW behavior. Therefore , the process of propagation in this period was always from mother tochild, which was different from thatof the first period. The process of acquiring this behavior by infants and juveniles
in this period is described below.
(a) Strengthening affinity to water. Infants are taken to the edge of the water during the period when they are dependent solely on their mother's milk fornourishment. While the mothers are engaging in SPW behavior, the babies
strengthen their affinity to water by being dipped in water, or by splashingwater by hand.
(b) Eating potato in the water. Infants eat fragments of potatoes that their mothers
drop in the water. This begins at about 6 months old.
(c) Acquisition of SPW behavior. Infants acquire SPW behavior when they are 1 一
2.5 years old.
Thus , the acquisition of SPW behavior begins in infants in the second period. In
this period, acquisition or propagation of SPW behavior occurred independentlyof sex. It can be said that precultural pressure is working toward acquiring thisbehavior. Therefore , the author calls the second period the period of preculturalpropagatIon.

494

S. Hirata et ale

3.1.3 Variations of SPW Behavior

3. 1.3. 1 From Fresh Water to Salt Water
During 1953-1954, SPW behavior was done on the edge of a brook running into
the sea. Monkeys never washedpotatoes with salt water,but used the fresh water ofthe brook. During the surveys of 1957 and 1958, many monkeys began to wash
potatoes in salt water. During the survey of December 1961 , all the SPW-monkeys
washed potatoes in both salt and fresh water. However, when they used fresh water
there were particular reasons for doing so: for example, when they were given
potatoes in the close vicinity of fresh water, or when subordinate monkeys avoided
coming near the seashore for fear of dominant individuals. In other words , SPW
monkeys preferred salt water to fresh water. For one thing , the quantity of fresh
water was limited. In dry per心心， the brook that ran into the sea dried up. Anotherreason was that if the monkeys became familiar with salt water, it would make thepotatoes taste good. The author presumes that these are the two main reasons why
the monkeys preferred salt water.

3.1.3.2 Seasoning Behavior
SPW behavior 尬， as described above , to dip a piece of potato into water by holding
it in one hand and brushing off any sand with the other hand. Imo , the originatorof SPW behavior, showed this typical behavior, but monkeys do not always brushthe pieces ofpotato. Often they let a piece ofpotato fall into shallow water and washthe sand offby rolling it with one hand on the bottom. Among the monkeys ofthe
first period, monkeys such as Eba, Sango , and Sasa rolled the potato more £時，
quently than they brushed it. However, during the second period another type of
behavior appeared. This consisted of dipping the potato into the water, gnawing it
once or twice , and then repeating this behavior. Monkeys collected potatoes andTable 2. SPW monkeys classified by three types of SPW behavior
Birth year

Age

B國typeBefore 1949
1951

Over 13
11

Eba, Nami
Semushi, Sango,

1952
1953
1954
1955
1956
1957
1958
1959

10
9
8
7
6
5
4
3

1960

2

BS-typeS-typeAome， Har材 iro

lmo

Nogi
Hama, Zabon

Zai

Sasa
Enoki
lka, Ego , NofujiEbi, Hamo
Namako , Eso ,SakuraSame, Eboshi

B-type, Brushing; BS-type, brushing-seasoning; S-type, seasoning.

Tsuru
Saba
Tsuge
lne
Nobori, Hasu, Tsuga

24 “ Sweet-Potato Washing" Revisited

495

took them to the seashore to carry out 由is type ofbehavior. The au也or considers
the function of this behavior to be seasoning the potatoes. Table 2 classifies individual monkeys according to these three types ofSPW behavior (B-type, brushing;BS-ty阱， brushing-seasoning; S-type, seasoning). B-type monkeys who retained
the old style were those who acquired SPW behavior in the first period, while
younger monkeys who acquired SPW behavior in the second period belonged to也e BS-type or the S-type. These monkeys were acquainted from their infancywith
eating potatoes in water,so they had first learned to eat potatoes with salt seasoning
or wet with water,and 血en acquired brushing behavior to remove sand.

3.2 Wheat Placer Mining (WPM) Behavior
3.2.1 Wheat Placer Mining Behavior
3.2. 1. 1 Acquisition of Wheat 向'acer Mining Behavior
The Koshima troop also has another prec叫tural behavior: wheat placer mining
behavior (Fig. 4). When grains of wheat were scattered about on the beach, themonkeys ate them by painstakingly picking up one grain after another. However, if
a monkey gathers up the grains ofwheat together wi出 some sand and then throws
them into the wate巳 it succeeds in separating the grains of wheat from the sandmoreeasil手 The grains float to 由e surface ofthe water, whereas the sand sinks. Thisis called wheat placer mining behavior,owing to its resemblance to the mechanismof gold mining.
This behavior, which was begun by Imo , was first observed by Kawamura in1956. Imo was then 4 years old and was well acquainted with SPW behavior. Table

Fig. 4. Wheat placer mining(WPM) behavior

In Kawai's (1 965) original paper, this behavior is called “ wheat washing" behavior. However, itis actually a bit different from “ washing" the wheat, and therefore we use the term “ wheat
placer mining" to avoid confusion.

496

S. Hirata et ale

3 shows the propagation ofWPM behavior from 1956 to 1962. By August 1962, a
total of 19 monkeys had acquired this behavior (38.7 0/0).

3.2. 1.2 Process of Propagation
In the 1957 survey,the onlyWPM-monkeywas Imo,who was also the originator ofthis behavior. However, during that yea巳 the researchers used wheat in a test to
analyze dominance rank. Because of this, the monkeys grew familiar with wheat,and this seemed to contribute to the rapid spread ofWPM behavior. Yoshiba andAzuma noticed 1m。這 WPM behavior and gave her the conditions which would
strengthen this behavior by burying wheat grains in sand and stamping them
down. This resulted in an increase in the number of monkeys who learned WPM
behavior. The propagation ofWPM behavior can be considered to be individualistic up to 1962. It is ofinterest to examine the course by which WPM behavior was
propagated from its initiation by Imo in 1956 until August 1962, and also theconditions in which the acquisition of this behavior took place.

(a) Lineage and playmate relationships. The propagation process for WPM behavior was similar to that for SPW behavior. Especially noticeable was the effect oflineage. Of 15 monkeys (not including 1-year-old infants) of Eba's lineage,to which
Imo belonged，的 used either WPM behavior or snatching behavior (see Sect. 3.2.2).
Nori's family also showed a high percentage of WPM behavior. As with SPW behavior, in Nami's lineage , only Jugo used WPM behavior.

(b) Age and sex. According to the data shown in Table 3,WPM behavior was mostly
acquired by monkeys aged 2, 3, or 4 years. Monkeys aged 1 year or older than 6
years were not as good as others at acquiring this behavior. In partie叫ar， none ofthe

Table 3. Age and year when monkeys acquired wheat placer mining (WPM) behavior andsnatching behavior
Age
Year

1956
1957
1958
1959

1. 5

2.。一 2.5

3.0-3.5

4.0-4.5

5.0-5.5

6.0

Adult

Imo ♀
{J ugo ♂)Ego ♀

Enoki ♀

Jugo ♂

Nofuji ♀，Ika ♂，(Zabon ♀)， Nogi ♀，Enoki(S) ♀

Sasa ♀

Zai ♂

Tsuge ♀，

Saba ♂

(Eso ♂)(Ebi ♂)

Eba s ♀

Ego(S) ♀，Saba(S) ♂

1961-62
1962 (Aug.)

Aome ♀

Zabon ♀

Eboshi ♂~Sakura ♀'的i ♂

Hama ♀， SangoS ♀

SameS ♂

Eso ♂

Tsuru ♂

Names in parentheses indicate incomplete acquisition.
Ssnatching behavior only.
的 WPM behavior + snatching behavior.

24 “Sweet-Potato Washing» Revisited497

monkeys over 12 years ofage (born before 1950) were seen to e油ibit WPM behavior. In adolescents and adults, sex differences became important, as they did with
SPW behavior,because of the differences in social status. Such sex differences were
not important in juveniles.

3.2.2 Snatching Behavior
3.2.2. 1 Snatching Behavior
Some monkeys watched the WPM-monkeys and snatched the grains of wheat
when they were thrown into the water. The author calls this snatching behavior. In
July 1959, an adult female , Eba, and 2-year-old Saba showed this behavior. Enoki
and Ego showed WPM behavior, but they often showed snatching behavior also
(Table 3). During the period from December 1961 to January 1962, Enoki and Ego
did not snatch any wheat from other monkeys , but only showed WPM behavior. In
August 1962, Sango and Same began snatching behavior in addition to Eba. Eba
and Sango were ranked as No.1 and No.2 among the females. When they approached other monkeys aggressively, the other monkeys ran away. Therefore Eba
and Sango could eat the wheat in the water without any effort. Same, on the other
hand, who was given a high degree of tolerance during cofeeding because he wasstill only 2 years 0祠， came close to monkeys engaging in WPM behavior and ate
wheat with them, or collected the grains which floated toward him, or consumed
leftovers after WPM-monkeys had gone.

3.2.2.2 Two Types of Snatching Behavior
As suggested above, there were two types of snatching behavior. One was collecting
the leftovers, as shown by Same. This was peculiar to juveniles, and developed into
WPM behavior later. The other type was plundering, as seen in the two adults Eba
and Sango. They did not perform WPM behavior themselves , but let WPM-monkeys throw the wheat and sand into the water for them. Their behavior was far more
effective than WPM behavior itself because they could monopolize the fruit ofother animals' labor by plundering.

3.3 Bathing Behavior
3.3.1 Acquisition of Bathing Behavior
The monkeys of Koshima, although they had been living on a small islet surrounded by the sea, were never seen to go into the sea before 1959. Even after they
were accustomed to salt water by SPW behavior, all that they did was just to dip
their hands and feet in water. None of them bathed in the water.
However, in the summer of 1959, Mrs. Mito attracted monkeys into the water of
Otomari Bay by throwing peanuts into the sea. Since then, some monkeys havegone into the sea to get peanuts. The first monkey who went into the sea was,according to Mrs. Mito , 2-year-old Ego. The author calls this behavior bathing
behavior (B-behavior, Fig. 5).
In the summer of 1960, several monkeys born after 1954 were observed to bathe.

498

S. Hirata et al.

Fig. 5. Bathing behavior

A thorough survey made in January and in the summer of 1962 produced thefollowing results: (1) of the 49 monkeys available for the investigation, 31 wereobserved doing B-behavior (63.2%); (2) all the monkeys born after 1955, except for
two l-year-old monkeys and Namazu, bathed in the water; (3) of the monkeys
born before 1955, only 6 individuals performed B-behavior (namely 2 solitary
males (Gosuke and Jugo) out of 14 males ,and 4 out of9 females). Gosuke probably
drowned while he was trying to swim to the other shore across the sea; Jugo swam
to the other shore in 1960 and swam back to the islet in the fall of 1964). No other
adults ever bathed in the sea, and they also hated even to dip their feet in.

3.3.2 Process of Propagation
3.3.2.1 Acquisition and Propagation

B-behavior quickly propagated to other members ofthe troop. Wi也in only 3years
after the first appearance ofbathing monkeys, almost all juveniles and adolescents
began to show this behavior. The level of acquisition in those who were born after
1955, excluding monkeys of less than 2 years old, was 96.19色) but the level ofacquisition in adults was ve可 low at 26.0% (6 out of23 adults).
There are two probable reasons for the speed of propagation. One is that theevent which gave rise to this behavior was humans throwing their favorite foodinto the sea. The other is that, unlike SPW and WPM behavior,bathing is a matter ofadaptation to a new habitat and of changing conservatism. This gives us a strong
interest in monkeys' conservatism, which is especially marked in adult males. The
rate of adaptability to a new habitat seems to be high in juveniles and adolescents ,medium in adult females , but ve叮 low in adult males.
3.3.2.2 Precultural Propagation

Infants are offered many opportunities to acquire B-behavior because the mothers
go into the sea with their infants clinging to their fur. When the mothers go into the24 “ Sweet-Potato Washing" Revisited499

sea, they do not pay any particular attention to whether or not their infants are
dipped into the water. Often infants are completely submerged in the water, andsometimes come close to being drowned. In this way, not long after their birth,
infants become adapted to bathing in water. As a result, infants accept the sea as apart of their habitat, as they do with the mountains , and feel no reluctance inbathing. Therefore，也e acquisition ofB-behavior is a precultural acquisition for infants.

3.3.3 Variation of Bathing Behavior
In B-behavior, almost all monkeys used quadrupedallocomotion in the ankledeep shallows. In deeper places, monkeys used bipedallocomotion. Often theybathed, dipped themselves in water up to their shoulders, or used quadrupedal
locomotion with only their head held above the water. With bipedallocomotion,
the degree of dipping themselves differed among monkeys: for some the water
only came up to their knees , others went in up to their waist, and others went in up
to breast height. There were 10 monkeys who swam: eight 2 to 5-year-old monkeys
and two solitary adult males. Some juveniles began to take a strong interest inbathing itself. They dived from rocks and enjoyed swimming. It can be said thatthese juveniles have developed the original bathing behavior into new practices of
avoiding the heat and just playing in the hot summer. They also dived under waterskillfully, and sometimes took seaweed from the bottom at a depth of 1 or 1.5 m.

3.3.4 Comparison with Other Troops
It is not unusual for Japanese monkeys to go into the river or the sea. Monkeys ofseveral other troops bathe in the river or in a pool. An interesting case is the
Jigokudani troop , where some monkeys go into a hot spring in the cold ofwinter(Suzuki 1965). It is considered to be a general habit ofJapanese monkeys to batheor swim, but, as seen in the Koshima troop, this habit should be recognized as acharacteristic ofthe troop rather than ofthe individuals. Another point to be notedis the adaptability and tradition ofthe troop in Japanese monkeys. It is surprisingthat until1959 , the strong traditions of the Koshima troop meant that they had
never gone into the water. However, once that strong tradition began to break down
for one reason or another, it could easily be removed.

3.4 “ Give-Me-Some" Behavior
3.4.1 Give-Me-Some Behavior
When a human observer put his hand into his pocket to take out some peanuts，也emonkeys waited, sitting in front ofhim, taking up a posture oflet-me-have-someplease. This behavior closely resembles that of a human child when he is given
sweets or cookies. The author calls this give-me-some behavior (GM behavior). GM
behavior could not always be seen when monkeys were given food. When they
were not psychologically calm , that 函， in a situation where they would easily bedis倒也edbyo也ers or by nearby dominant monkeys,they did not show GM behavior.

500

S. Hirata et ale

3.4.2 Acquisition and Propagation
The initiator, the date of first occurrence, and the process of propagation of GM
behavior are unknown. In 1960, Azuma noticed that Kaminari, one of the leader
males , showed GM behavior. Many other monkeys must have performed this behavior at a much earlier date. Out of 47 monkeys available for the test, 37 performed GM behavior (two l-year-old monkeys were not tested). This was 78.80/0 ,which was higher than that for SPW behavior. Among 24 males, 19 (79.1 0/0) showed
GM behavior, and among 23 females , 18 (78.20/0) did so. No difference due to sex
could be observed. The high percentage ofacquisition by adults was characteristicof this behavior. There were 10 monkeys who did not perform GM behavior (5males and 5 females). Included in these were three children ofNami (Nasi, Namako,
and Namazu).

3.4.3 Meaning of GM Behavior
Why did GM behavior begin, and how did it propagate? Judging from the intellectual faculties of monkeys, the acquisition of this behavior cannot simply be asCI油ed to imitation. The remarkable differences between this behavior and SPW
and WPM behaviors is that it was performed by all the adult males, including thesolitary males. This behavior pattern is believed to be quite general among Japanese monkeys,because GM behavior can be witnessed in other troops,“thoughit
remains individualistic and is not a general behavior pattern in these troops.
Compared with other monkeys in Japanese monkey parks , the monkeys at
Koshima are distinguished by the fact that they have never bitten or attacked anyone, and have seldom threatened humans since the start ofprovisioning. In othermonkey parks , relationships between monkeys and humans are not always peacefuI. At Koshima, there are few sightseers, and it is mainly local monkey lovers or
researchers who make contact with monkeys. Thus; the monkeys do not need tosnatch their food by threat or attack, and they have learned to wait. In short, what ischaracteristic ofthis troop is their gentle, friendly attitude towards humans. Thus,
GM behavior is one manifestation ofan attitude toward humans born out offriendship and composure on the part of monkeys. The friendly attitude of all the monkeys towards humans can be taken as a kind of"implicit" preculture (Kawamura 1956).

3.5 The Four Behaviors ComparedIn each section, the author has suggested that three factors , i. e. , age, sex, and kinship ,were important in the acquisition and propagation of the four newly acquired
behaviors. The author would like to compare the four behaviors with each other.
Figure 6 shows the change in the ratio of monkeys who performed each behavior
as of 1962 as a function of age. The curves of SPW, WPM , and B-behaviors are
similar,while that of GM behavior is of a different form. The ratio of monkeys who
showed the first three behaviors began to increase in juveniles, reached a peak inadolescents , and decreased in adults in 1962. However, the highest ratio of GM
behavior (I 000/0) was seen in monkeys of 6 一 11 years old (adolescent and adult) ,一

24 “ Sweet-Potato Washing)) Revisited

100

,

'

.

.

.‘

..

、、

、'，'

、'，'

'

40

、、

鼠，。

,
. ‘,
.
'
,

、、

(♂)
小mhω
戶M
已。EMOOZω
倡

..
'

60

Fig. 6. The change in the ratio of monkeys
who performed each behavior as of 1962 asa function of age

..

,',

..
.','.'
,
•,
'
-ok
,'
.
.
'

80

501

.

,

,

• -SPW..o··WPM
一← B

20

。

-• GM

2--3

8--11

6~7

4~5

12--

Age

,

'

‘..
、

a'

、

‘..
、

av

n

。

‘..

,
4

、

..‘ .‘

',

,

。

。

由』τ
。喝何ω
向A咕。』喘
V口
Skn
像。白人惘
h。
oA眉目2

4

3

2

-• Male

。

2--3

- 0-

Female

4--5.

6~7

Age

8""'-'11

12""'-'

Fig.7. Average number of newly acquired
behaviors by males and females in each age
class

and even adults more than 12 years old showed a high percentage. The similarity
between SPW behavior and WPM behavior is shown in Fig. 6. The only differenceis that the age ofacquisition ofSPW behavior was lower than that ofWPM behavior
in the period ofindividual propagation. This difference is due to the relative difficulty of acquisition. SPW behavior has sometimes been observed in other troops
such as Takasakiyama, Ohirayama,Arashiyama, and Gagyusan , although it remains
individualistic and has not been propagated to other monkeys in these troops. It
seems to be possible to acquire SPW behavior incidentall抖 n WPM behavior,monkeys have to go through the procedure of collecting wheat by hand and taking 祉，together with any sand they have picked up , to the water before they can select thewheat they want by putting the mixture into the water. WPM behavior is a more
complex activity. Figure 7 shows the differences in behavior acquisition in relation
to the sex and age oftheanimals. In juveniles and adolescents , sex differences had
no effec t. In adolescents and 8 to II-year-old adults , the males showed a lower

502

S. Hirata et ale

Table 4. Mean number of newly acq凶red behaviors (MNNB) by monkeys of each lineage
MotherSango Eba

No. of children 4
MNNB
4.0

8
3.6

Imo

Aome

Harajiro Natsu Nori

Utsubo Nami

2
3.3

2
3.3

3
3.0

2

7

1. 6

1. 6

3
2.6

4
2.6

percentage ofacquisition than the females. This is due , as has been explained, tothe differences in status of males and females.
In each section, the author has referred to the differences in acquisition caused
by lineage. For example, the children ofSango and Eba acquired these new behaviors very readily,while Nami's children were slow (Table 4). In a society ofJapanesemonkeys , mother-child relations are known , but it is difficult to determine whichanimal is the father. Therefore , it is difficult to pursue this genetic aspect with
scientific rigor. Nevertheless ,it is interesting that a difference in acquisition ability
according to lineage has been suggested by the data.

3.6 Environmental Basis of Precultural Phenomena
The precultural behaviors seen above all developed from the monkeys' foraging
behavior and their relation to humans. That 函， they were all derived from provisioning. Provisioning made great changes in the naturallife of the troop. Anotherimportant factor is the natural environment. In Koshima , three different environments-precipitous mountains with thick woodland, the sandy beach, and thesea-are beautifully integrated. Before the monkeys were provisioned, the mountains were their only habita t. After provisioning, they came to know contrasting
environments such as the sandy beach and the sea. That 函， a new, different environment, or niche , was introduced into their naturallife. The major precultural behaviors of the Koshima troop are connected with the sands and the sea. It is doubtful
whether such inventive behaviors as SPW and WPM would have been developedin their previous niche. Therefore the monkeys have invented adaptive behavior
in response to changes in the environmental conditions. Behavioral adaptabilityor plasticity in response to changes in the environment are important when we
think about the evolution ofbehavior in animals.

4 Return from Revisit: Koshima Monkeys Afterwards
Here we return from Kawai's (1965) paper. What happened to the Koshima monkeys afterwards? A total of more than 450 monkeys were recorded from 1952 until
1999. None ofthe monkeys who experienced the emergence ofthese precultural
behaviors is alive now, but their descendants are still dipping sweet potatoes into
the sea, throwing grains of wheat into the water, and bathing in the sea. Thesebehaviors have been transmitted over the generations.

24 “Sweet-Potato Washing)) Revisited503

Table 5. Examples of the variation in SPW behavior within individuals
Type of SPW behavior
Name (sex, age)

Se

Ri

Rw

Uri (♀， 15)
Cha (♀， 7)
Chinu (♂， 4)
Chisha (♀， 1)
Ume( ♀， 12)
Mebaru (♂， 4)
Megi (♀， 1)
Utsugi (♀， 6)

18
30
2

8

33
39

12
14
3
2
25
13

2

8
3

39
7
35

31
4
21

3

11

40
2
8

14
3
5

Udo( ♀， 3)
Kuri (♀， 16)

Kemushi (♂， 5)
Keshi (♀， 2)
Kurumi (♀， 13)
Mono( ♀， 5)

Momiji (♀， 2)
Kuma( ♂'的

Br

Rh

PI

Ga

Rr

Others

2
8

3

4
2

10
2
3

2
2
4
4

Se, Seasoning; Ri , rinsing; Rw, rubbing in water; Br, brushing; Rh , rubbing between hands; 凹，plundering; Ga, gathering; Rr, rubbing on rock.
The data in the body of the table show the number of times each behavior type was observed.
Uri , Ume , Utsugi , and Udo are siblings. Kuri , Kurumi , and Kemushi are also siblings. An
indented name indicates a mother-child relationship. The individual whose name is indented
is a child of the previous individual whose name is not indented.

Kawai and colleagues conducted an intensive follow-up study on these behaviors (Kawai et al. 1992; Watanabe 1994). Five new behavioral patterns have been
added to the repertoire of sweet-potato washing, and six to wheat placer mining.
An interesting case is “pool-making;' which is efficient for wheat placer mining.
When grains ofwheat are scattered on the beach while it is still wet at low tide, somemonkeys dig out some sand and make small pools from the water that oozes up.
They then dip a piece ofsweet potato or sweep nearby grains ofwheat into the pool
before they eat them.
By reanalyzing the systematic data taken during 血is follow-up study, we caninfer the process of monkeys' acquiring SPW and WPM behaviors. Table 5 shows
examples of the variation in SPW behavior within and between closely related
individuals. Different behavioral patterns of SPW were distributed throughout
almost all members ofthe group , and no monkey engaged persistently in anyone
specialized behavior (for details ofthe methods ofstudy and descriptions ofeach
behavior type, see Kawai et al. 1992; Watanabe 1994). Although it is difficult tointerpret these data exactly in terms of the mechanisms underlying the process ofacquisition, we have the impression that these behavior types are established bytrial and error by each individual rather than by copying every method from otherS. Hirata et ale

504nunυAUAU
QUGUA• -SPW..•.. WPM

且zqLU(法)MgZω眉苦。zhog
喝崗
..

100

。

1-2

3-4

5-6

Fig. 8. The ratio of gathering behavior as a SPW. and
WPM-related behavior by age class. The data werecollected from 69 individuals. A total of 1662 samples
of SPW behavior were divided into nine categories(see Table 5 and Kawai et al. 1992). A total of 2805
samples of WPM behavior were divided into eightcategories: throwing, sweeping, pool-making;plundering， remo討ng， screening, screening while walking, andgathering (see Kawai et ale 1992)

7~至

Age

monkeys. The motor patterns used in these SPW behaviors seem to be general in
Japanese monkeys, and can appear spontaneously in each individual. Figure 8
supports Kawai's (1965) hypothesis about the development of SPW and WPM
behavior. In infants and juveniles, the gathering of other monkeys' leftovers was
the predominant SPW- and WPM-related behavior. This type ofbehavior decreasedin adults, and they engaged in their own methods ofprocessing sweet potatoes orgrains ofwheat. Infants first learn to eat seasoned or washed pieces ofsweet potato,
or floating grains of wheat, by gathering others' leftovers. They then begin to engage in SPW or WPM behavior by themselves.
Now,SPW behavior can be seen everywhere on the beach whenever sweet potatoes are given. However,wheat placer mining has become less common. The main
reason for this is that the amount of provisioning has been reduced because the
pop叫ation of monkeys on Koshima Island became too large (Watanabe et al.1992).
Potatoes are now given only a few times per year. Sweet potato washing and wheat
placer mining began under provisioning, so it is quite natural that these behaviors
should have changed as the degree of provisioning has changed.
There is another reason why wheat placer mining behavior has become lesscommon. Imagine the snatching behavior described above. Now that the amountofprovisioning is reduced, the competition for wheat is much more severe. Monkeys lose wheat if they throw grains into the water because dominant individuals
will snatch them away; it is better to pick them up and eat them directly from theground. Wheat placer mining can be seen when the monkeys have almost finishedeating and there are still a few grains left on the ground mixed with sand. In thecase of sweet potato washing , however, the animals can run away carrying the
sweet potato in their hands if a dominant monkey approaches. The fact that one or
two pieces of sweet potato per monkey are enough is also relevan t. For these reasons , wheat placer mining has become less common but sweet potato washing canbe seen even under greatly reduced provisioning. In addition , seasoning is now
the predominant behavior type in sweet potato washing, and real washing has
become very rare. In the 1960s, all sweet potatoes were covered with soil, while now
they have already been washed in the market, and there is no need for the monkeys
to wash offthe soil.

24 “ Sweet-Potato Washing" Revisited505

Table 6. Precultural behaviors and the sand-digging test
Result of sand-digging test

No. of newly acquired behaviors

o

234
221

A, B
C, D
E

1

6
3

7
3

13

3

Uncertain result because of a failure to do an appropriate tes t.
The results of the tests were classified from A (best) to E (worst).
The numbers of individuals are shown in each category.

aAnother change for the Koshima monkeys is that they have begun to eat fish
(Watanabe 1989). Fish-eating was first reported to happen sporadically among
adult males, and initially the habit did not spread to other troop members. In 1982,
about 3 years after the first observation, four adult females were observed to eat raw
fish. This was the turning point for this habit to spread among the troop. Most
members then began to eat raw fish , and this continued until1986. The reason may
be that the population had increased to about 100 at that time, which caused a
scarcity offood.
Besides the intensive observation of the behavior of the monkeys , some field
experiments were conducted on Koshima. In 1961 , Kawai developed a simple test
called the “ sand-digging test:' A human experimenter buried a peanut on thebeach in front of a monkey. Then all traces of disturbed sand were carefullysmoothed away. When Ego was tested, she immediately dug out the peanut. Later,
Kawai and colleagues conducted a systematic study of this sand-digging test on
the Koshima monkeys (Tsumori et al. 1965). Eighteen monkeys easily found thepeanut. Five other monkeys found it in the seco.nd trial. The results for each monkey were classified into five grades from A (best) to E (worst). A correlation was
found between the results of the sand-digging test and the number of precultuI叫
behaviors they acquired (Table 6).Another experimental studywas conducted by
Higuchi (1992). He introduced an open operant box to the island, and examined
the acquisition and propagation of panel-pressing behavior. Out of 74 monkeys inthe troop , 34 acquired the panel-pressing behavior. He concluded that most of thetransmission of this behavior occurred through local enhancement, along withindividual trial and error.
Imo , the originator of SPW and WPM behavior, died on May 21 , 1972, but she isstill alive in current literature (e.g. , de Waa11999; VogeI1999). Ironically, discussions about cultural phenomena in animals have become heated since her death.
Galef (1990, 1992) picked up the example of sweet-potato washing to argue about
imitation and culture in animals ,Visalberghi and Fragaszy (1990) conducted experimental studies on the emergence and diffusion of food-washing behavior in
captive capuchin monkeys and CI泊 -eating macaques, and Tomasello et al. (1993)
discussed culturallearning in human and nonhuman primates.
Longitudinal observations of fr

506

S. Hirata et al.

which was seen in the Arashiyama troop (Huffman 1984, 1996; Huffman and Quiatt1986). A 3-year-old female began to handle stones in a peculiar manner in 1979,
and this stone-handling behavior propagated to other troop members. This behavior initially spread only among individuals of the same age-class as the initiator,
but subsequently passed down from older to younger individuals in successive
generations. It is now a commonly seen behavior among most individuals of thistroop. The second example is the technique of grooming (Tanaka 1995 , 1998).
Tanaka investigated the techniques of grooming in the Shiga-A troop , and identified four patterns of grooming behavior. An analysis of the distribution of eachtechnique in three maternallineages showed the possibility of social transmissionof the grooming technique from adults to infants.
By looking at animals other than Japanese monkeys , we can find ver叮ycωonsp抖icαωu­ousexamp
抖lesof“:chimpanzee cultur
閃es~九.Iongitudi旭na叫叫I investigations of wild chimapanzees at several different sites in Africa have been clarifying the behavioral diversity between different study sites, which cannot be explained by ecological or
genetic theories (Goodalll973; McGrew 1992; Wrangham et al. 1994; Sugiyama
1997; Boesch 1996; Matsuzawa 1998; Whiten et al. 1999).

5 Back to the Question of Culture
Half a century has passed since the start of the research on Koshima monkeys. The
study of nonhuman primates has accumulated data from both the field and thelaboratory, and by both naturalistic observation and experimental manipulation.
Have we succeeded in casting a different light on human culture by keeping ouroutlook broader? The examples from Koshima Island clearly show that the socialtransmission of behavior occurs in Japanese monkey society, but it seems to beinappropriate to answer yes or no to the question ofwhether nonhuman primateshave culture. A valuable way forward would be , as Kawamura (1956, 1965) remarked, to trace each step and consider the evolutionary pathway (e.g. , van Shaik
et al. 1999). In the first place, intensive and longitudinal observations have revealed highly organized permanent social structures in many species of monkeys
and apes. Such permanent group living 函， as Imanishi (1952) suggested, one condition for the establishment of a culture. In the second place, studies of social
learning in animals have revealed more precise mechanisms of social transmission of a behavior. The process of sociallearning is now divided into several categories , such as social facilitation , stimulus enhancement, emulation, program-level
imitation,action-level imitation, etc. (Tomasello 1990; Byrne and Russon 1998). In
these terms , the growing body ofknowledge has been making it clear that imitation is more difficult for nonhuman primates than was expected in the 1950s:
monkeys do not imitate,but are influenced by stimulus enhancement (Visalberghi
and Fragaszy 1990); chimpanzees do emulate, and much less frequently they imitate (Whiten et al. 1996). In addition, monkeys do not teach others to do anything ,and chimpanzees only do so extremely rarely (Boesch 1991). Therefore, it can besaid that imitation and teaching, the two most important elements in human ma-

24 “Sweet-Potato Washing" Revisited507

terial culture, cannot be found in monkeys, and is only seen in chimpanzees to avery limited extent (Myowa-Yamakoshi and Matsuzawa 1999). However，也etrans­mission ofmaterial culture in humans is not always accompanied by teaching andimitation either. The fact that human children imitate does not mean that they
always imitate (Whiten et al. 1996). It is quite natural to assume that stimulus
enhancement and emulation are involved in some cases of the transmission ofcultural phenomena in humans as well as imitation and teaching. Although recent
experimental studies have been trying to distinguish and separate every social
learning process, it is also possible to look at the problem in reverse, that is, we
could also try to find a link between stimulus enhancement, emulation, and imitation in terms of cognitive mechanisms.
Drawing a line between culture and nonculture is beyond the scope of thispaper. Instead, we would like to conclude by saying that humans and monkeys
might share some traits in the social mechanism and cognitive capacity which
comprise human culture, and this is more true for apes and humans. The invention and propagation of precultural behaviors shown by Koshima monkeys arevaluable examples when thinking of such phenomena. In Koshima, the sixth generation descendants of the monkeys in the initial study periods are still engaging
in sweet-potato washing.

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