Last week was a significant week in the history of marriage. North Carolina became the thirtieth state to pass a constitutional amendment defining marriage as between one man and one woman. And shortly after the passage of Amendment One, Barack Obama became the first sitting American president to unequivocally voice his support for same-sex marriage.

In the wake of these important developments, a host of civic and religious leaders weighed in. Lauding the president’s decision, New York City mayor Mike Bloomberg quickly noted, “No American president has ever supported a major expansion of civil rights that has not ultimately been adopted by the American people.”

Evangelist Billy Graham, on the other hand, lamented that the meaning of marriage was even open to debate. “The Bible is clear,” Graham said in a statement. “God’s definition of marriage is between a man and a woman.”

Archbishop Timothy Dolan also expressed his sadness at the president’s comments in support of the “redefinition of marriage.” The leader of the US Conference of Catholic Bishops added that the hierarchy “cannot be silent in the face of words or actions that would undermine the institution of marriage, the very cornerstone of our society.”

Remarks like those from Graham and Dolan are representative of the “traditional” Christian view of marriage. Proponents of this view see marriage as a monolithic institution. They believe that marriage was established by God in the Garden of Eden and has largely remained unchanged since.

But this view of marriage ignores the long and complex history of the institution’s evolution and development. Christian marriage has not always been between “one man and one woman.” For most of recorded biblical history, polygamy was seen as normative. For example, the patriarch Jacob had at least three wives (Genesis 30), King David had at least eight, and his son Solomon had 700 (1 Kings 11:1-3)—not to mention 300 concubines!

Even during the early centuries AD when the books of the New Testament were being written and compiled, polygamous marriages were common. In several of his epistles, Paul specified that those in positions of leadership in the early church should be the “husband of but one wife” (see Titus 1:6, 1 Tim. 3:2).

Marriage in the early church bore little resemblance to the institution we know today. It was primarily an institution of the state. Once a Christian couple had been legally married, they would attend liturgy, received the Eucharist together, and be blessed by the local bishop. The features we recognize as typical of a wedding ceremony—the use of a simple white veil and the symbolic joining of the couple’s hands—did not begin to appear until the time of Augustine (354-430).

It was another five hundred years in the West before weddings took place in churches, by which times the majority of marriages were monogamous. And it was not until the late Twelfth Century that marriage was considered a sacrament—a view that the Protestant Reformers argued against vehemently in the Sixteenth Century.

Given this complex history, it is no wonder that Christian scholars and laypeople alike have asked whether “a stable core that could be called the ‘essence of marriage’” can be discerned at all (Vorgrimler, “Sacramental Theology,” 284).

Christians of various traditions and denominations struggle to come to a common understanding of marriage. And when other voices—Jews, Muslims, Christians, Atheists, Humanists, to name but a few—are brought into the conversation about how to shape our public policies concerning marriage, the task becomes increasingly complex.

President Obama was certainly aware of the diversity of perspectives surrounding gay marriage. In his landmark interview last Wednesday, he acknowledged the internal struggle he has experienced as he has tried to reconcile his faith with his political views. He expressed a desire to be “sensitive to the fact that for a lot of people… the word marriage was something that evokes very powerful traditions, religious beliefs, and so forth.”

Through his conversations with his own family, friends, and spiritual advisers, the President gradually underwent an evolution in his beliefs. He ultimately came to the conclusion that at the core of his Christian commitment was the conviction to treat others the way in which he wants to be treated.

Debate in the U.S. over the meaning of marriage and the question of whether to expand its definition to include members of the LGBT community is likely to continue for months and years to come. Recent polls indicate that Americans have been evolving in their views on gay marriage over the last few years. If we Christians are to be honest with ourselves and reckon with our own history, then we must remain open to the possibility that the meaning of marriage may evolve—just as it has always done.