Is It Safe To Eat Boiled Brain?
On a cold winter evening ten years ago, Richard Wrangham was lying in front of the fireplace in his Boston home. The flames carried his thoughts to the earliest ancestors of man, who used such a fire for cooking.
He envisioned a small group of Homo erectus crouching around a campfire in Africa, toasting a wildebeest leg and sharing scorched pieces of tuber. Cooking is one of the few activities that only humans use, as the primatologist from Harvard University knew.
He also knew that pre-digesting food while cooking helps people conserve energy while digesting it. And suddenly he realized that cooking could have given the pre-humans a great evolutionary advantage. According to his theory, it enabled the brain to grow dramatically.
For Wrangham, the answer to a great mystery of human development lies in the saucepan: Where did people get the energy from to afford big brains?
The central nervous system of Homo sapiens is insatiable. In a calm newborn, the brain uses 60 percent of the energy. In adults it is 25 percent; Monkeys run their brains on average with around eight percent of the energy they consume.
Overall, however, humans do not consume more calories than comparable animals - small women have about the same metabolic rate as large chimpanzees.
Energy boost from meat
People saved energy by shrinking their digestive tracts once they switched to a higher quality diet with more meat, is the common explanation for this.
Wrangham believes that our ancestors also started cooking so they could eat the same number of calories with less effort.
The primatologist is now underpinning the idea from the late 1990s with a large amount of new data. "Even small changes in diet can have big effects on survival and reproduction," he says.
Some of his colleagues are enthusiastic. The new results showed "the fundamental importance of the energy budget for human evolution," says Robert Foley of Cambridge University in the UK.
But not all researchers are convinced that the first meal was cooked 1.6 million years ago when the brain of the species Homo erectus enlarged dramatically.
Even the scientists, who are critical of the thesis of cooking, agree, however, that something decisive must have happened in the energy budget of the pre-humans. Between 1.9 million and 200,000 years before the present, human ancestors tripled the size of the brain.
Apparently, one key to this was meat consumption. Even the oldest stone tools, 2.7 million year old artifacts from Gona in Ethiopia, were used by hominids to cut up carrion.
But it took over a million years for the anatomy to change. Only a 1.6 million old erectus skull had twice as much brain as the heads of older species, says paleoanthropologist Alan Walker of Pennsylvania State University. At that time, finds show that Homo erectus dragged animal carcasses into its camp. His teeth, jaw, and intestines became smaller.
Pythons as a taster
The usual explanation is that the pre-humans were a better hunter and carrion-seeker than their predecessors.
But a diet of gnu tartare and antelope sashimi alone cannot explain the dramatic change, says Wrangham. Other animals would have adapted to raw meat with larger teeth. Homo erectus must have started frying the prey, with root vegetables as a side dish or substitute, if the hunters were unsuccessful. "Cooking produces soft, high-energy food," he says.
He did this in the laboratory with Stephen Secor from the University of Alabama. Secor studies the metabolism of amphibians and reptiles.
That is why the team set up a comparison test with 24 pythons from Burma. They got their meat either cooked or raw. The researchers measured the energy consumption during digestion using the oxygen demand. If the snakes got cooked meat, they saved almost 13 percent of their energy.
A pilot study with mice also supports Wrangham's thesis: If the rodents were fed with cooked meat, they gained 29 percent more weight in five weeks than conspecifics who were given raw meat. According to the preliminary results, they were also four percent longer, despite consuming fewer calories overall.
Chewing consumed energy
The heat from the cooking fire gels the collagen matrix in the meat and opens up tightly woven carbohydrate molecules in plants so that the nutrients are easier to absorb. This reduces the time it takes to chew. Chimpanzees take an average of five hours to chew their food, while hunters and gatherers who cook their food chew only an hour a day.
"It's such a nice statement," says Leslie Aiello, President of the Wenner-Gren Foundation in New York. She, too, interprets the smaller teeth of Homo erectus in such a way that he no longer had to chew a lot of hard food. "If only we had evidence of fire!"
Indeed, this is the stumbling block for Wrangham's thesis: Cooking requires control over fire. Indisputable evidence of habitual cooking would be stone fireplaces or clay cooking vessels.
But the oldest finds of charred flint, seeds and wood in a fireplace-like pattern are 790,000 years old and come from Israel. Wrangham admits that that would be far too late for his theory. Evidence for fire is often ambiguous.
In fact, a dozen research groups interpret finds as evidence of campfires nearly old enough for Wrangham's thesis. For example, Rutgers University paleoanthropologist Jack Harris found burnt stone tools and clay in the Olduvai Gorge in Tanzania and Koobi Fora in Kenya that are 1.5 million years old. There are traces of Homo erectus in both places.
Maybe just a bush fire
But where there was once smoke, a cooking fire did not necessarily burn. None of the research groups can rule out that naturally occurring fires have left the charred traces. Harris argues, however, that cooking fires reach 600 to 800 degrees Celsius, while bush fires sometimes only get 100 degrees.
The Homo erectus experts, however, are not convinced that the pre-humans were cooks. Walker says they would otherwise have discovered traces of campfires with bones or tools found nearby.
The neurobiologist John Allman of the California Institute of Technology in Pasadena adds: "I believe Wrangham's process is wrong. Cooking is only linked to the rapid growth of the Neanderthals' brain." The paleoanthropologist Loring Brace of the University of Michigan also says: "Prehumans had fire under control about 800,000 years ago, but they systematically used it to prepare food for less than 200,000 years."
The lack of evidence does not lead all professionals to reject Wrangham's thesis. Carel van Schaik of the University of Zurich believes that cooking played an important role early on, along with other adaptations that allowed a larger brain.
Leslie Aiello says the growth in the head was apparently a happy coincidence, several factors reinforced each other: more meat consumption, a smaller bowel, cooking and perhaps greater efficiency in walking and running upright.
The sequence of these energy-saving innovations is at the center of the debate between the researchers. Evidence of cooking is the hardest to find. "But the threads are gradually coming together," says Aiello.
This text is taken from the current edition of Science, the international science magazine published by the AAAS. German adaptation: Christopher Schrader.
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