The Nut-Cracking Chimpanzees of Tai Forest

Produced by Christophe Boesch and Hedwige Boesch-Achermann (25 min).

(jl) These are the so-called common chimpanzees; bonobos have not been observed doing this. Obviously this is an activity dependent on a supply of nuts as well as coordination and intellect, etc. It may also be limited to a sub-species of chimps found in western Africa. (Note that my comments are usually prefaced or followed by (jl))

1. Darwin and nut cracking (jl)

This activity was known to Darwin (1871):

" as for tool use, the chimpanzee, in a state of nature cracks a native fruit, somewhat like a walnut, with a stone."

(jl) All to often we hear about a "new" discovery that either was previously known or is overinterpreted as more human-like than previously thought.

2. two types of nuts
3. lots of calories in nuts

Chimps may spend 2.5 hours per day and get 4000 calories from nuts They can use their teeth but its difficult and slow.

4. the tools

The hammers-rocks and wood- are used to crack the nuts; skill is needed in order to open but not completely smash them. Young chimps may not even hit the nut.

The anvils appear to be flat rocks but stumps and limbs also are used.

5. dominance and ownership

do they really "own" the anvils?

(jl)What does that mean?

dominance gives access to the best tools

young chimps are forced to use inefficient tools

the young may share tool with mother

6. sharing

Sharing is only among friends and direct relatives; access depends on dominance.

7. skill involved

(see above)

8. hand dominance

Individuals have hand preferences but there is no species dominance like that in humans with nearly 90% favoring their right hand.

(jl) what about throwing--while standiing?

A recent study at Yerkes reported both sexes of common chimps threw primarily right-handed when in a bipedal stance--but much less so from a quadrapedal stance. This and other hints make me consider that bipedality predisposed or "preadapted" homo erectus for a number of human-like activities.

9. females crackers in trees

Much of the nut-cracking seems to be done by females; they use tree limbs as anvils.

It appeared there was lots of right hand pounding as the right foot holds. This may be just a coincidence.

10. reproduction and maternal care of infants

infant acquistion of nut cracking skill

There is little interest when very young but around two years there is a definite interest.

They beg from mother's mouth rather than take pieces from the anvil. Recall "mouth feeding" in humans! Most primates learn about food in this way -- "kissing" their mother's lips for a taste. Mother NHP's rarely are seen "teaching" appropriate foods.

Three year olds begin to show an interest in cracking their own nuts. This is described as "copying" the mother but this is interpretation that may not stand up See readings (Bryne, 1995, and Tomasello, 1994) on issues here. Mothers may set the stage for individual "trial & error" learning without explicit teaching or even modelling--just social priming.

Five-year olds are successful. It takes about 4 years of practice to actually get the nuts out.

There were scenes of young chimps collecting nuts for mom to crack!

Young chimps stay with mothers till about 12 years old.

a quick mating interlude!

Note lack of "foreplay" , quick arousal, and presence of infant.

11. questions

what about getting tools?

(I didn't see anything about how tools were found or "made.")

relation to fertility and ultimately "fitness"

Does eating nuts markedly change the life-style of these chimps, e.g. do they reproduce more rapidly because of the high-calorie foodstuff?