The non-profit Nonhuman Rights Project asked a New York state court to establish the "legal personhood" of chimpanzees.
Cambridge – Although chimpanzees obviously don’t cook, they share with humans the psychological capabilities to do so, a new study by two US scientists shows.
This suggests, they say, that once humans managed to control fire, they would have learned to cook quite quickly, supporting claims that cooking originated early in human evolution.
The psychological capabilities required for cooking include motivation, patience, inhibitory control, causal understanding and planning, write the scientists, Felix Warneken from Harvard
University and Alexandra G. Rosati from Yale University, in the London-based Royal Society’s journal Proceedings B.
The transition to a cooked diet marked a major shift in human evolution and may have contributed to the development of larger brains, according to the scientists, who point out that brain tissue
consumes a large amount of energy and that cooking – compared with a diet of fruits, leaves and raw meat – increases the energy available from foods.
Among the many unanswered questions is whether the control of fire, thought to have been used first for heat and light, led to cooking only after a significant delay. Were the last common ancestors of
humans and apes cognitively capable of cooking?
To shed light on this, the scientists performed nine experiments on chimpanzees (Pan troglodytes), humans’ closest living relatives.
The scientists say their experiments showed that chimpanzees prefer cooked foods, comprehend the transformation of raw food that occurs when it is cooked, were willing to wait – and also to give up raw food already
in their possession – to acquire cooked food, and would transport as well as save raw food in anticipation of having it cooked.
“To our knowledge, this is the first evidence that apes can plan for the future by saving food for future transformation.”
During the experiments, which were voluntary for the chimpanzees, an individual ape sat across from the experimenter, separated by wire mesh or bars, at a table with a sliding top. The experimenter placed
the options on the tabletop, pushed it forward, and the chimpanzee could indicate its choice by pointing or touching one option.
In the first experiment, the researchers learned that the apes preferred a slice of cooked sweet potato to a raw one. The second showed that when given the choice between receiving one raw slice immediately or having to wait a minute to receive either three
raw slices or three cooked ones, they opted more often to wait for the cooked slices.
Further experiments used two containers: a control device and a mock-up cooker with a false bottom hiding a pre-cooked slice of food.
When a raw slice of food was placed in the “cooker,” which was then shaken by the experimenter, the cooked slice came out. When the same procedure was followed with the control device, the raw slice came out unchanged.
The chimpanzees preferred the cooker. They resisted eating raw food and put it into the cooker instead, put different kinds of food – and only edible items – into it, and brought raw food from one side of the room to the other to put into the cooker.
Some even saved food for future “cooking” by waiting three minutes until the experimenter showed up with the cooker and control device.
“Given that chimpanzees in these studies inferred novel opportunities to transform their food after minimal experience, this suggests that early hominins may have also been able to detect and use existing opportunities in their environment to cook foods,” the scientists
“Wild chimpanzees will calmly monitor the movements of natural fires, and even actively seek out roasted seeds from burnt habitats,” they observed.