Extension 14- Experiments

A chimpanzee drinks from free surface water (river, lake, pond) by bending over on the banks and to touch the water with pursed lips and then  to suck it.

He cannot make his hand to a bowl such as man. That is explained In note 2 of Extension 13 

Chimpanzees live in and at the proximity of trees and these forms cavities and holes where sometimes water collects. Here the animal cannot drink in the normal way. 

One of the ways to drink it, is to pick a leaf (or leaves) from a nearby plant or tree and to form this to a gag in the oral cavity. He pushes the blade probably inside with the finger knuckles (he has not the skill to do so with fingertips), so that for each push there arises a harmonica-like folds (the literature talks about folding 3 cm wide).

He then takes the gag from his mouth, the tongue pushes it probably out, and inserts it with one hand in the water of the hole. The water penetrates inside and stays locked in the folds. He brings back the gag in his mouth and squeezes the water out there.

At first it seems an incomprehensible way of doing, why not just fold the gag with the hands? Answer: his thumb is too far away to be able to it, see the just mentioned note.

From the literature are also cases reported that leaves in the mouth are crunched to a sponge to serve as absorption of water  hard to reach.

The reason for this experiment was to understand more about the how and why of this drinking behavior.

  1. a. The experiment with plants leaves as water holder, summer 2014

When the idea for this experiment was born a rhubarb plant in my garden just reached maturity. I cut two pieces respectively 21 x 24 and 28 x 28 cm of leaf, , with the leaf vein in the middle. From a nearby chestnut tree I picked 6 leaves (average 17 x 8 cm).

 A plastic cup served as oral cavity (, inside: high 8.2 cm, diameters 5.0 (bottom) and 7.3 cm on the edge). I pushed with my fingertips of one hand the leaf inside and took care to make  as many harmonica folds as possible.

Of course I missed the tongue as a knockout body, at pulling out, the gag  lost somewhat of its ball shape but with help from the other hand I restored that again. 

I took the bulb lightly with one hand and inserted him a few seconds in a wide bowl with water.

Pulled him back and squeezed him out over a measuring cup and recorded the amount of water that came out. Once the gag comes above water begins to drip out, I took care to get the gag in one stroke above the measuring cup, at appr. 30 cm distance.  In reality, the chimp will maintain his head also in close proximity to keep the loss as much as possible limited. Result of 3 types of leaves is as follows:



Insert number.

 water in cc


 rhubarb 24x21










 rhubarb 28x28



















6 chestnut leaves













Extensie 14p1

1. A piece cut from two leaves for the test.












Extensie 14p2

2.Test attributes.












Extensie 14p3

3. Press inside with fingertips.












Extensie 14p4

4. Gag is formed.












Extensie 14p5

5. Gag after 3 x use, please note that veins are snapped and resilience to form harmonica cavities is less.











b. Discussion

It is expected that the first insert is most effective because when squeezing the leaf fibers break and lose their resilience (so less form a harmonica). The test results confirm that. The result is very much influenced by speed of transfer and the power of squeezing.

It is imaginable that at each time a squeezing with the tongue also the choose bruise the gag slightly and that the gag went to function more like a sponge. So that the leaf which began as a collection of angular cavities, gradually changed into a sponge, in fact also a collection of cavities but then very small. In other words that one method resulted from the other and that there is no question of a choice between two methods

After the retreat I had always to fashion the gag somewhat again. I then realized that a chimpanzee does not possess that skill. He does not have the fine locomotion of fingertips form a gag (that property is supported in extension 13, section a, note 2 and 3 of table). So that is the reason to use the oral cavity as a tool in forming a gag. He couldn't do that like humans do and used the mouth cavity as a tool to form a gag.

c. Conclusion

The chimps uses plant leaves to get water from difficult accessible places.

The test shows that per turn13 to 30 cc can be transferred. That is a quarter teacup of water.