It is one of the enduring questions of religion and science, and lately of American politics: When does a fertilized egg become a person?
Abortion foes, tired of a profusion of laws that limit but do not abolish abortion, are trying to answer the question in a way that they hope could put an end to legalized abortion.
Across the country, they have revived efforts to amend state constitutions to declare that personhood -- and all rights accorded human beings -- begins at conception.
From Florida to California, abortion foes are gathering signatures, pressing state legislators and raising money to put personhood measures on ballots next year. In Louisiana, a class at a Catholic high school is lobbying state legislators as part of a civics exercise.
"We have big and small efforts going on in 30 states right now," said Keith Mason, co-founder of Colorado-based Personhood USA. "Our goal is to activate the population."
Critics deride the effort as the "egg-as-person" movement and say it threatens in vitro fertilization; some kinds of birth control, including IUDs and pills; and stem cell research. They say that Americans will reject it as a government intrusion into their privacy.
"It's a backdoor abortion ban," said Ted Miller, spokesman for NARAL Pro-Choice America, which has worked with Planned Parenthood and other abortion rights groups to defeat such measures.
Since the mid-1970s, polls have found that about three-quarters of Americans support legalized abortion in at least some circumstances.
But this year, for the first time since the Gallup Poll started asking people in 1995 whether they identified themselves as "pro-life" or "pro-choice," a slight majority of Americans (51%) picked "pro-life."
Proponents of personhood measures root their hopes in the Supreme Court's 1973 Roe vs. Wade decision, in which Justice Harry Blackmun wrote for the majority that a fetus is not legally a person.
Establishing personhood would topple the rationale for legal abortion, their thinking goes, though many people on both sides of the abortion debate consider this logic farfetched.
Defeats of personhood measures around the country -- notably in Colorado, which in 2008 became the first state to put a measure before voters -- have not daunted proponents, a loose confederation of evangelical Christian and Catholic antiabortion groups.
Mason said he had been inspired by other struggles -- against slavery, for women's suffrage, for gay rights.
"I don't agree with the homosexual agenda, but I say, look at the tenacity of what they have done to fight for what is right," he said.
"I don't believe that just because we will not get enough votes in an election that we should not do this. I don't recall Martin Luther King checking the polls to see if he was right on civil rights."
Today, Mason will join activists in Sacramento to announce a signature-gathering campaign for an initiative to amend California's Constitution and define a person as a human starting at conception.
Two recently minted stars of the antiabortion movement are behind the measure: the Rev. Walter Hoye, who went to jail last year after violating an Oakland law designed to keep protesters away from patients entering abortion clinics, and Lila Rose, a UCLA student who has made undercover videos purporting to show legal violations at Planned Parenthood.
The American Life League, a well-funded conservative Catholic group, is advising Hoye and Rose on the initiative, which would require about 690,000 valid signatures to get on the ballot. The group is also helping with initiative campaigns in Colorado, Florida, Missouri and Montana.
Earlier this year, the legislatures of Montana and North Dakota rejected personhood measures, but the close votes alarmed supporters of legal abortion.
In Montana, the state Senate passed a bill calling for a constitutional amendment on personhood, but the bill died in a House committee after a tied partisan vote, according to Allyson Hagen, executive director of NARAL Pro-Choice Montana. "There was a simple majority support for it, which was pretty scary," Hagen said.
In North Dakota this year, the state's House of Representatives passed a similar measure, but the state Senate rejected it.
"I realize it's been defeated in every state where it's been attempted, but I am not discouraged," said Hoye, who has founded the California Civil Rights Foundation to push the initiative. "Everywhere I go from now on, we are going to be talking about personhood. Imagine the discussion statewide on whether the child inside the womb is human or not."