FAITH LAPIDUS: Welcome to THIS IS AMERICA in VOA Special English. I'm Faith Lapidus.

CHRISTOPHER CRUISE: And I'm Christopher Cruise. This week on our program, we learn why some American Indian tribes are growing faster than the rest of the country. In some cases tribes are moving to restrict membership and are even expelling members to control growth. Later, we look at language and the mind -- how certain word choices might help you discover if a person is lying.

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FAITH LAPIDUS: In populations, the "rate of natural increase" is a rate based on the number of births minus the number of deaths. It does not include migration. In the United States the rate of natural increase is about one percent a year. However, over the past 10 years, growth rates for some American Indian tribes have been two to three times higher than the national average.

The federal government recognizes 566 American Indian and Alaska Native tribes within the United States. In some ways the tribes are nations within a nation. They can make their own laws on their reservation lands. And their governments have complete authority to decide who can be a member of the tribe. Tribal citizenship is based on the blood lines of ancestors.

CHRISTOPHER CRUISE: Some Native Americans are returning to their communities because of their tribes' increasing wealth from gambling operations and other businesses. But fast growth has been difficult for some tribes, while others wish they had more members.

The Tulalip Tribes are based near Everett, Washington, in the Pacific Northwest. Their growing membership is a source of pride for John McCoy, a tribal member and a Washington state representative. He says part of the reason for the tribe's growth is improved health care.

JOHN MCCOY: "We're living longer. Our babies are surviving birth."

Another reason for the growth, he says, is an increase in jobs on reservations, with the increase led by tribal gaming operations.

JOHN MCCOY: "So we have our peoples coming back from other states. They're coming home because there is an economy."

The Tulalip tribes have had a 22 percent growth rate over the past 10 years. Some tribes around the country have grown even faster.

FAITH LAPIDUS: Some of those tribes have felt the need to increase membership requirements in order to control the sharp growth.

In California, some tribal governments have even made cuts in their membership. The biggest reason appears to be financial. Having more members means a smaller share for each individual in the sharing of tribal wealth.

For example, the Puyallup Tribe in western Washington state currently pays each member 2,000 dollars a month in profit sharing. Tribal members voted to limit new enrollments in 2005.

CHRISTOPHER CRUISE: Like the Puyallups, the Grand Ronde Tribe in Oregon operates a successful casino. Members of the Grand Ronde Tribe have changed their membership requirements three times since 1999.

Recently tribal members voted to keep tight enrollment requirements in place. For example, new members must have a parent who was on the membership list at the time of their birth.

Before the vote, Dee Edwards posted an emotional video on YouTube saying that the rules split her family and left out her grandchildren.

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A former member of the tribal council, Andy Jenness, recorded that video for Ms Edwards. He says he supports rules that will not divide families, even if that means smaller payments for him.

ANDY JENNESS: "The amount of growth that is acceptable to me is that of natural birth and the tribe growing at the natural rate, whatever that is. If that means I have less in my per capita check, so be it."

FAITH LAPIDUS: But other members warned against opening the "floodgates" of tribal membership. Over the years, people have criticized so-called tribal jumpers. These are Native Americans whose ancestry includes connections to several tribes. "Jumping" means giving up citizenship in one tribe to move to a wealthier one.

If too many people do that, it can reduce shares of profit and put more pressure on tribal services that everyone wants.

CHRISTOPHER CRUISE: Yet there are also tribes that would welcome new members. Among them is the Colville Confederated Tribes in northeastern Washington state.

Council member Ricky Gabriel has proposed that members vote to ease the blood requirement in the tribe's constitution. That way more children from mixed marriages could become members. He says his proposal has had a lot of positive reactions.

RICKY GABRIEL: "The elders are extremely happy about this. They're pushing hard. They're seeing their grandchildren not be able to be enrolled."

Membership in the tribe currently requires that a person have at least one-fourth Colville blood. It takes just a couple of generations of marrying outside the tribe to put children at risk of being excluded from membership.

Mr Gabriel's proposal would change the requirements and recognize blood from any Indian tribe toward the minimum. Several tribes around the country including the Tulalips and Puyallups have ended all blood requirements. They now base membership on direct descent from tribal members on historic membership lists.

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FAITH LAPIDUS: Pronouns can be very useful -- in fact, more useful than you might even imagine. Pronouns are words like I, we, you, they, he, she and it. We use them -- another pronoun -- in place of nouns and noun phrases.

James Pennebaker has written a new book called "The Secret Life of Pronouns." Mr Pennebaker is a professor, but not an English professor. He is a professor of psychology at the University of Texas at Austin. He says word choices show more about what people are thinking that they might realize.

JAMES PENNEBAKER: "What they do is tell us how a person is thinking, where they are paying attention. So, for example, if I use the word I a lot, it tells a researcher that the person is paying attention to themselves, to their feelings and their thoughts."

CHRISTOPHER CRUISE: Professor Pennebaker decided to do some research. He and his student assistants fed large amounts of written material into a computer. They used a program designed to recognize patterns in word use to analyze what people were saying or writing.

JAMES PENNEBAKER: "We get huge bodies of text, it could be conversations or books or poems or whatever, and by analyzing the way they are using pronouns and also articles, prepositions and conjunctions -- this is a group called function words -- we get a sense of how they are thinking and how they are connecting with others."

For example, Mr Pennebaker looked at writings from personal blogs before and after the terrorist attacks on the United States in 2001.

JAMES PENNEBAKER: "We studied 70,000 blog entries for 1,000 people from two months before to two months after September 11th, and what you find is that on September eleventh the entire culture drops in the way it uses 'I,' 'me' and 'my.' It increases the use of 'we' and we can track how long these language changes occur. With 'we,' for example, they go on for the next two months."

FAITH LAPIDUS: Another time, he recorded conversations at an event where young singles were brought together to go on dates with people they had never met before. Analysis of the conversations proved to be a good predictor of whether any two people would continue seeing each other after that event.

CHRISTOPHER CRUISE: And there are other uses for this kind of language analysis. James Pennebaker says one of the most promising areas of study involves lie detection. Remember those function words he talked about -- articles, prepositions, conjunctions, as well as pronouns? How people use these words, he says, can give investigators a pretty good idea of whether someone is lying or trying to hide something.

JAMES PENNEBAKER: "What we find is pretty consistent: when people tell the truth they use the word 'I' at much higher rates. They are owning what they are saying. When they are lying they tend not to use 'I.' They are almost avoiding self-referencing."

Professor Pennebaker says this method is still far from being a "lie detector." But it can be a useful tool for investigators, and using a computer can improve the results.

In one test, students had to decide from a statement if a person was lying. The students were correct just 52 percent of the time -- about the same as if they had guessed. But when a computer analyzed the word use, it found the liars with 67 percent accuracy.

FAITH LAPIDUS: Most of the research has been done with English texts. But Professor Pennebaker says the software has produced similar results using texts in Spanish, Chinese and other languages.

JAMES PENNEBAKER: "What we find is pretty much the same thing. When people are using the words 'I,' 'me' and 'my' at high rates, they tend to be more honest, they tend to be a little bit more depressed, they tend to be a little bit more anxious than people who do not use 'I's' and that holds up across all these different languages and even ancient languages like ancient Greek."

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CHRISTOPHER CRUISE:Our program was produced by Brianna Blake, with reporting by Tom Banse and Greg Flakus. I'm Christopher Cruise.

FAITH LAPIDUS: And I'm Faith Lapidus. You can find transcripts and MP3s of our programs along with other activities for learning English at voaspecialenglish.com. You can also find our podcasts in the Apple iTunes Store. And you can join the conversation on Facebook and Twitter at VOA Learning English. Join us again next week for THIS IS AMERICA in VOA Special English.

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（來源：VOA 編輯：Rosy）