The Biblical story of Adam and Eve, long dismissed as fiction by many, is gaining the attention of some geneticists and researchers of humanity's origins, According to recent research into the human  genome, all people now living can trace their ancestry back to 10  Adams and 18 Eves, all of whom emerged from a small population of  individuals in prehistoric Africa. Furthermore, all 28 can be traced  back to one woman, the original Eve, who lived nearly 200,000 years  ago.   Dr. Douglas C, Wallace of the Emory University School of Medicine in Atlanta, Georgia, has developed a human family tree, based on mitochondrial DNA, which is passed from mother to daughter, starting with the aforementioned 18 Eves. Meanwhile, Dr. Peter A. Underhill and Dr. Peter J. Oefner of Stanford University have constructed a similar tree based on the Y chromosome, whose characteristics are handed down from father to son, beginning with the 10 Adams.   Geneticists believe that the ancestral human population from which the first Eve was born had about 2,000 members. Approximately  144,000 years ago, well after the first Eve, this population began to split, with some subgroups remaining in Africa and others spreading to Europe, Asia, and the rest of the world. Wallace found that nearly all Native Americans belong to the mitochondrial lineages he labeled A, B, C, and D, while Europeans belong to two different lineage groups he called H through K and T through X. Not surprisingly, the A through D lineages are also found in Asia, .confirming the widely held theory that the Americas were populated by Asians traveling across a land bridge from Siberia during the last Ice Age.   In 1998, however, Wallace and his colleagues discovered the rare X lineage, which is found in Europe but not in Asia, among northern Native American tribes, suggesting that prehistoric migration to the Americas was more complex and followed more routes than was originally thought. The out-of-Africa theory has net gone unchallenged. Some researchers, pointing to flaws in the assumptions and findings of geneticists, support an alternative theory of multiregional evolution, one that holds that modern humans arose in Africa nearly 2 million years ago and evolved as a single species. They then spread from Africa over a long period and interbred with local populations, including Neanderthals  and other archaic humans. Recent fossil evidence, they say, points to the interbreeding of older populations and newer groups of modem humans in places as widespread as Portugal and Australia.   Both tides of the debate, however, tend to agree that the old rigid divisions of race, ounce considered scientific gospel, have crumbled. Research has shown no evidence for “race” at the genetic level. As a result, the Biblical account of mankind's origin from a common ancestor has shed some of its mythical status. Commented Dr. Underhiil: “We are all Africans at the Y chromosome level and we are really all brothers.”