(FORTUNE Magazine) – What ethnic group in the U.S. has grown fastest--without the help of immigration? Native Americans, whose numbers soared 137%, to about two million, from 1970 to 1990.

Not surprisingly, the astounding success of casino gambling on Indian reservations--and subsequent windfalls for tribal members--has lots of people reevaluating their genealogy. Since Congress passed the Indian Gaming Regulatory Act in 1989, 115 tribes in 23 states have started some form of casino gambling. Says Rick Hill, chairman of the National Indian Gaming Association: "It's been the best economic development tool in the last 115 years for tribes."

The Shakopee Mdewakanton Dakota tribe in Minnesota, which numbers just 100, owns three roaring casinos 25 miles outside of Minneapolis. Last year each member over 18 collected a $400,000 dividend. Accordingly, the tribal enrollment office has been swamped with calls about membership. Hint: To qualify you need to be one-quarter Mdewakanton. In Connecticut the Mashantucket Pequots' membership increased 44%, to 332, in the three years since its Foxwoods Resort Casino has been open. Membership inquiries pour in.

Even without the magnet of money, more American Indians are rediscovering their heritage. The casino-less Cherokee Nation's ranks have swelled to 169,000 today, from 37,000 in 1983.

- Jacqueline M. Graves