VOA标准英语2011--Sense of Smell Jumpstarted Brain Evoluti

（单词翻译）

Sense of Smell Jumpstarted Brain Evolution

Mammals have much bigger brains than other animals. Scientists aren't sure exactly why, but new research published this week in the journal Science suggests it might have something to do with mammals' acute sense of smell.
Researchers used computed¹ tomography or CT scans to analyze² the skulls⁴ of 190-million-year-old mammals found in a Jurassic-era fossil bed in China. These tiny critters, co-existed with the giant, meat-eating dinosaurs⁵ and probably survived by being nocturnal.
But to be active at night meant the mammals had to have "very special sensory⁶ adaptations," says Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, and a member of the research team that studied the prehistoric⁷ mammal skulls.
He says the CT-scans helped the team construct a virtual brain case for two of the ancient mammals. "In this study we have found that the large brain is becoming larger primarily because the olfactory⁸, or the smelling part of the brain, become very big and also the part related to skin tactile⁹ sensation also becomes big."
Luo says the acute sense of smell and touch that helped mammals survive among the predatory dinosaurs is clearly visible in their ancient anatomy¹⁰.
"So the new evolutionary¹¹ biology idea from this study of fossils is, maybe, a capacity to smell very well is as important, even more important than hearing and that the tactile sense probably played a big role too."
Luo says these Jurassic-era mammals - including the tiny Hadrocodium, whose skull³ was smaller than a paper clip - had brains that were two or three times larger than any mammal relatives before them.
"Hadrocodium has this big head, small mammal, relative to the body size, it has already achieved about the same range of brain size as modern mammals."
Luo was thrilled to see this impressive brain development in our 190-million-year-old mammalian relatives. It's an important evolutionary milestone¹² that helped make mammals - and humans among them - one of the Earth's dominant¹³ animal classes.