Editor's Note: Jonathan Dudley is the author of "Broken Words: The Abuse of Science and Faith in American Politics."

By Jonathan Dudley, Special to CNN

Over the course of the 2012 election season, evangelical politicians have put their community’s hard-line opposition to abortion on dramatic display.

Missouri Rep. Todd Akin claimed “legitimate rape” doesn’t result in pregnancy. Indiana Senate candidate Richard Mourdock insisted that “even when life begins in that horrible situation of rape, that it is something that God intended to happen.”

While these statements have understandably provoked outrage, they’ve also reinforced a false assumption, shared by liberals and conservatives alike: that uncompromising opposition to abortion is a timeless feature of evangelical Christianity.

The reality is that what conservative Christians now say is the Bible’s clear teaching on the matter was not a widespread interpretation until the late 20th century.

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In 1968, Christianity Today published a special issue on contraception and abortion, encapsulating the consensus among evangelical thinkers at the time. In the leading article, professor Bruce Waltke, of the famously conservative Dallas Theological Seminary, explained the Bible plainly teaches that life begins at birth:

“God does not regard the fetus as a soul, no matter how far gestation has progressed. The Law plainly exacts: 'If a man kills any human life he will be put to death' (Lev. 24:17). But according to Exodus 21:22–24, the destruction of the fetus is not a capital offense… Clearly, then, in contrast to the mother, the fetus is not reckoned as a soul.”

The magazine Christian Life agreed, insisting, “The Bible definitely pinpoints a difference in the value of a fetus and an adult.” And the Southern Baptist Convention passed a 1971 resolution affirming abortion should be legal not only to protect the life of the mother, but to protect her emotional health as well.

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These stalwart evangelical institutions and leaders would be heretics by today’s standards. Yet their positions were mainstream at the time, widely believed by born-again Christians to flow from the unambiguous teaching of Scripture.

Televangelist Jerry Falwell spearheaded the reversal of opinion on abortion in the late 1970s, leading his Moral Majority activist group into close political alliance with Catholic organizations against the sexual revolution.

In contrast to evangelicals, Catholics had mobilized against abortion immediately after Roe v. Wade. Drawing on mid-19th century Church doctrines, organizations like the National Right to Life Committee insisted a right to life exists from the moment of conception.

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As evangelical leaders formed common cause with Catholics on topics like feminism and homosexuality, they began re-interpreting the Bible as teaching the Roman Catholic position on abortion.

Falwell’s first major treatment of the issue, in a 1980 book chapter called, significantly, “The Right to Life,” declared, “The Bible clearly states that life begins at conception… (Abortion) is murder according to the Word of God.”

With the megawatt power of his TV presence and mailing list, Falwell and his allies disseminated these interpretations to evangelicals across America.

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By 1984, it became clear these efforts had worked. That year, InterVarsity Press published the book Brave New People, which re-stated the 1970 evangelical consensus: abortion was a tough issue and warranted in many circumstances.

An avalanche of protests met the publication, forcing InterVarsity Press to withdraw a book for the first time in its history.

“The heresy of which I appear to be guilty,” the author lamented, “is that I cannot state categorically that human/personal life commences at day one of gestation.... In order to be labeled an evangelical, it is now essential to hold a particular view of the status of the embryo and fetus.”

What the author quickly realized was that the “biblical view on abortion” had dramatically shifted over the course of a mere 15 years, from clearly stating life begins at birth to just as clearly teaching it begins at conception.

During the 2008 presidential election, Purpose Driven Life author Rick Warren demonstrated the depth of this shift when he proclaimed: “The reason I believe life begins at conception is ‘cause the Bible says it.”

It is hard to underestimate the political significance of this reversal. It has required the GOP presidential nominee to switch his views from pro-choice to pro-life to be a viable candidate. It has led conservative Christians to vote for politicians like Akin and Mourdock for an entire generation.

And on November 6, it will lead millions of evangelicals to support Mitt Romney over Barack Obama out of the conviction that the Bible unequivocally forbids abortion.

But before casting their ballots, such evangelicals would benefit from pausing to look back at their own history. In doing so, they might consider the possibility that they aren’t submitting to the dictates of a timeless biblical truth, but instead, to the goals of a well-organized political initiative only a little more than 30 years old.

The opinions expressed in this commentary are solely those of Jonathan Dudley.