WITH THE DEFENSE of Marriage Act on California’s March ballot, the subject of gay rights is likely to move to the forefront of the political debate. Already, many Democratic candidates are said to be desperate to avoid taking a position on this controversial measure while many Republicans wish that the issue would simply disappear.

The initiative, placed on the ballot by religious conservatives, defines a legally valid marriage as being one between a man and a woman, thereby closing the door on the growing effort through courts and legislation to legalize gay marriages. The debate surrounding the hot-button proposition will inevitably broaden to social attitudes toward homosexuality.

Given the extremely controversial nature of the topic, it is useful to examine the historical record.

Human civilizations have demonstrated an enormous diversity of attitudes toward homosexual behavior. In ancient Greece and Rome, a root of Western civilization, homosexuality was widespread and tolerated and, at times, even exalted as a higher form of love. By contrast, the other root of Western civilization, the Jewish Old Testament, regarded homosexuality as a crime against nature and God, drawing the death penalty.

Non-Western civilizations exhibit much the same wide range of attitudes. Under some Chinese dynasties, homosexual activity was tolerated or encouraged among the elite, while puritanical Maoist China regarded it as a vile Western perversion and reportedly underscored this attitude through summary executions.

Similarly, the question of what constitutes a legally valid marriage has generated an amazing variety of answers in different times and places. As heirs to the Judeo-Christian tradition, we unthinkingly consider a marriage as involving one man and one woman, although such strict monogamy is a relatively recent and rare social attitude.

Some form of polygamy has been recognized in the vast majority of human societies, and even today is probably accepted in more countries than not.

This diverse tradition provides a historical context for the forthcoming ballot initiative. One fact immediately stands out: views of homosexuality have varied, views of marriage have varied, but there has never been a human society, past or present, which authorized homosexual marriages. For the United States to legalize gay marriages would be an act unprecedented in all recorded history.

The reason is simple.

Marriage has generally served the role of providing a stable home environment for the young biological children of the married couple, and this implies a man and a woman. Other relationships, from the traditional European mistress to modern American cohabitation, simply do not require as strong a legal bond. And while homosexual couples today are not prevented from living together or informally acting as “man and wife,” even up to the point of undergoing unofficial marriage ceremonies, it is unreasonable to require society to provide formal legal sanction to such a relationship.

Consider the implications. Since homosexual marriages are unprecedented, while polygamy is commonplace throughout all history, it is morally inconsistent for U.S. law to begin allowing the former without legalizing the latter as well. And the basic libertarian argument in favor of gay marriage, namely that no other individual is harmed by allowing a man and a man to marry, can be taken much, much farther as well.

For example, how can one then deny the right of two men and three women to achieve personal fulfillment by entering into a legally valid group marriage — again, no other individual is directly harmed. Either the official nature of marriage should be kept as currently restricted, or it must be amended to the point where the entire institution becomes almost unrecognizable.

Today’s America is an extremely diverse land, with an amazing array of different social traditions and subcultures. If our common legal structures were to be bent or stretched to accommodate one, they must be made to accommodate others as well. Legalizing gay marriages today means legalizing polygamy or group marriages tomorrow.

Ron Unz, a Silicon Valley entrepreneur, is chairman of the “Voter Rights 2000” campaign reform initiative and a candidate for the U.S. Senate.