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次の英文はScience誌（２００７年６月１５日）に掲載された　Ann Gibbons氏の記事"Food for Thought"　を一部改変したものです。

次の文章をよく読んで、問題１～６に答えなさい。

　　Richard Wrangham was lying beside a fire at home on a cold winter night 10 years ago when his mind wandered to the firsthominids to cook food. 　

As a Harvard University primatologist who studies wild chimpanzees in Africa, Wrangham knew thatcooking is one of the few uniquely human abilities. 　

He also knew that our habit of preparing our food by heating it allows us to spend less energy on digestion. 　And he suddenly realized that cooking is not merely the basis of cultinary culture. 　

(1)It would have given our ancestors a big evolutionary advantage. 　

He argues that cooking paved the way for the dramatic expansion of the human brain and eventually fueled intellectual accomplishments such as cave painting. writing symphonies,and inventing the Interenet. 　

In fact, Wrangham presents cooking as one of the answers to a long-standing riddle in human evolution : Where did humans get the extra energy to support their large brains?


　　 Expanding the brain demands a new supply of energy, because human brains are voracious. 　

The brain consumers 60% of the energy expended by a resting newborn baby. 　

And a resting adult's brain uses 25% of its energy, as opposed to 8% used on average by ape brains. 　

But humans consume about the same amount of calories as smaller-brained mammals of similar body size.


　　　One classic explanation is that humans saved energy by shrinking their digestive organs, effectively trading brains for guts as (2)they shifted to a higher quality diet of more meat. 　

That theory is now gathering additional support.

Wrangham thinks that in addition, our ancestors got cooking, giving them the same number of calories for less effort.

Other researchers are enthusiastic about the new results. But many aren't convinced by Wrangham's arguments that the first cooked meal was prepared 1.9 million to 1.6 million years ago, when the brain began to expand dramatically in Homo errectus (H. erectus ).

They think that although saving energy by shrinking the gut may have been important, the culinary explosion came later, perhaps during the evolution of our own species less than half a million years ago.


　　　Even those unsure about the role of cooking in human evolution agree that something crucial must have happened to our ancestors' energy budget.

Line up the skulls of early hominids and you'll see why: From 1.9 million to 200,000 years ago, our ancestors tripled their brain size.　


　　The earliest members of the human family, including the Australopithecines that lived from 4 million to 1.2 million years ago, had brains about the size of chimpanzees. 　

The brain didn't expand significantly until just after H. erectus appeared in Africa about 1.9 million years ago, with a brain that eventually averaged 1000 cc. or about twice the size ofa chimpanzee's. 　

The next increase in brain capacity came 500,000 to 200,000 years ago with the evolution of our own epecies, whose brains average 1300 cc. and of Neanderthals (1500 cc).


　　What spurred this dramatic growth in the H. erectus skull? 　

Meat, according to a longstanding body of evidence.

The first stone tools appear about 2.7 millions year ago, along with evidence that hominids were using (3)them to cut up animals they had killed. 　

But big changes don't appear in human anatomy until more than 1 million years later, when a 1.6-million-year-old skull of H. erectus shows it was twice the size of an Australopithecine's skull, says anthropologist Alan Walker.　At about that time, archaeological sites show that H. erectus was moving animal bodies to campsities for further preparation and sharing: its teeth, jaws, and guts all got smaller. 　

The traditional explanation is that H. erectus was a better hunter and ate more raw meal than its small-brained ancestors. 　


　　　(ァ)But a diet high in raw meat alone isn't enough to account for these dramatic changes, says Wrangham.　

He notes that H. erectus had small teeth- smaller than those of its ancestors- unlike other carnivores that adapted to eating raw meat by increasing tooth size. 　

He agrues that whereas earlier ancestors ate raw meat. H. erectus must have been cooking it. "Cooking produces soft, energy-rich foods," he says. 　　


　　To support his ideas, Wrangham went to the lab to measure the nutritional impact of cooking. He found almost nothing in food science literature and began to work with physiologist Stephen Secor, who studies digestive physiology in animals. 　

Secor's team fed 24 snakes one of four diets consisting of the same number of calories of beef; cooked ground beef, cooked intact beef, raw ground beef, or raw intact beef. 　

Then they estimated the energy the snakes consumed before, during, and after (4)they digested the meat. 　Snakes fed cooked beef spent 12.7% less energy digesting it and 23.4% less energy if the meat was both cooked and ground "　　

By eating cooked meat, less energy is expended on diestion: therefore, more energy can be used for other activities and growth,' says Secor.

　　
　　Secor also helped Wrangham design a study in which they found that mice raised on cooked meat gained 29% more　weight than mice fed raw meat over 5 weeks. 　

The mice eating cooked food were also 4% longer on average, according　to early result. Mice that ate raw chow weighed less even though they consumed more calories than those fed cooked　food.


　　(ィ)The heat from cooking makes the food earier to chew, and the calories in the food earier to absorb. 　

This translates into less time spent chewing: Chimanzees spend 5 hours on average chewing their food whereas 　hunter-gatherers who cook spend 1 hour chewing per day. 　

　　The immediate changes in body sizes in the mice also suggest that our ancestors would have been able to get rapid　benefits out of cooking, says Wrngham. 　

That's why he thinks there would be little time between learning to cook and　seeing anatomical changes in humans- and why he thinks early H. erectus must have been cooking. Less chewing would lead to smaller jaws and teeth, as well as to a reduction in gut size- changes seen in H. erectus.

Those changes would be favored by selection.

　　Wrangham's analysis of nutritional, archaeological, and primatological data adds up to a hypothesis that hot cuisine　fueled the brain. 　

"It's such a nice explanation," 　says anthropologist Leslie Aiello. 　She says the smaller teeth in H.erectus indicate to her that (5)it wasn't chewing much tough raw food : "Something must be going on. 　If only there　were evidence for fire."　


　　And that's the stumbling block to Wrangham's theories : Cooking requires fire. 　Clear evidence of habitual cookingrequires stone hearths or even clay cooking pots. 　

Solid evidence for hearths, with stones or bones circling patces of　dark groud or ash, has been found no earlier that 250,000 years ago in several sites in southern Europe. 　

Burned bones,　stones, ash, and charcoal 300,000 to 500,000 years ago have also been assigned to hearths. 　

And burned flints, seeds, and wood found in a hearth-like pattern have been cited as signs of controlled fire 790,000 years ago. 　

But even the earliest of those dates are long after the dramatic anatomical changes seen in H. erectus, says Wrangham.

He notes that evidence for fire is often ambiguous and argues that humans were roasting meat and roots around the campfire as early as 1.9 million years ago.


　　Indeed, there are a dozen claims for campfires almost that ancient. Anthropologist Jack Harris has presented evidence of burned stone tools 1.5 million year ago, along with bruned clay at two sites.

H. erectus has been found at both sites. 　

Claims by other researchers include animal bones burned at high temperatures 1.5 million years ago, and　clay burnt at high temperatures 1.4 millions years ago. 　

But where there is smoke there isn't necessarily cooking fire:

None of these teams can rule out beyond a doubt that the burns came from natural fires, although Harris argues that　cooking fires burn hot at 600℃ to 800℃ and leave a trail different from that of bush fires, which often burn as low as　100℃.


　　All the same, those most familiar with H. erectus aren't convinced they were chefs. Walker says that if the species was cooking with fire, he and others should have found campfires associated with its bones and stone tools. Others agree:Lording Brace notes that less than 200,000 years ago is about the time evidence appears for earth-oven cookery :　"While fire has been under control back near 800,000 years, its use in the systematic preparation of food has only been　over the last 100,000-plus years."


　　Others think that cooking may have played an important role early on, along with other adaptations to expand human brainpower. 　

As Aiello observes, the big brain was apparently the lucky accident of several converging factors that accentuate each other. Critical sources of energy to fuel the brain came from several sources- more meat, reduced　guts, cooking, and perhaps more efficient upright walking and running.

The order in which our ancestors adopted these　energy-saving adaptations is under hot debate, with the timing for cooking hardest to test.


注　　hominids　　ヒト　　primatologist　　霊長学者 　H. erectus　　ホモ・エレクトス Australopithecines　アウストラロピテクス属 physiologist　生理学者　flints　火打ち石