SAT阅读材料：Learning and Microbes

　　Learning and Microbes Lets start from a simple fact Each person shelters about 100 trillion microbes But scientists cannot rear a vast majority of these bacteria in their labs to identify them and learn their characteristics. The implication is staggering.

　　For example, Are people, as a result of their microbe hosting difference, require, favor, or demand different ways of learning? Do our brains influenced in any way by this difference?

　　In the early 1900s, scientists discovered that each person belonged to one of four blood types. Now they have discovered a new way to classify humanity: by bacteria. Each human being is host to thousands of different species of microbes. Yet a group of scientists now report just three distinct ecosystems in the guts of people they have studied.

　　Its an important advance, said Rob Knight, a biologist at the University of Colorado, who was not involved in the research. Its the first indication that human gut ecosystems may fall into distinct types.

　　The researchers, led by Peer Bork of the European Molecular Biology Laboratory in Heidelberg, Germany, found no link between what they called enterotypes and the ethnic background of the European, American and Japanese subjects they studied.

　　Nor could they find a connection to sex, weight, health or age. They are now exploring other explanations. One possibility is that the guts, or intestines, of infants are randomly colonized by different pioneering species of microbes. The microbes alter the gut so that only certain species can follow them.

　　Whatever the cause of the different enterotypes, they may end up having discrete effects on peoples health. Gut microbes aid in food digestion and synthesize vitamins, using enzymes our own cells cannot make.

　　Dr. Bork and his colleagues have found that each of the types makes a unique balance of these enzymes. Enterotype 1 produces more enzymes for making vitamin B7 , for example, and Enterotype 2 more enzymes for vitamin B1 .

　　The discovery of the blood types A, B, AB and O had a major effect on how doctors practice medicine. They could limit the chances that a patients body would reject a blood transfusion by making sure the donated blood was of a matching type. The discovery of enterotypes could someday lead to medical applications of its own, but they would be far down the road.

　　Some things are pretty obvious already, Dr. Bork said. Doctors might be able to tailor diets or drug prescriptions to suit peoples enterotypes, for example.

　　Or, he speculated, doctors might be able to use enterotypes to find alternatives to antibiotics, which are becoming increasingly ineffective. Instead of trying to wipe out disease-causing bacteria that have disrupted the ecological balance of the gut, they could try to provide reinforcements for the good bacteria. Youd try to restore the type you had before, he said.

　　Dr. Bork notes that more testing is necessary. Researchers will need to search for enterotypes in people from African, Chinese and other ethnic origins. He also notes that so far, all the subjects come from industrial nations, and thus eat similar foods. This is a shortcoming, he said. We dont have remote villages.