Opposition MPs questioned the motives behind a call to study the Criminal Code definition of a human being, suggesting it naturally leads to a debate on criminalizing abortion.

NDP and Liberal MPs raised the question in speeches Friday that called for their colleagues to vote against Conservative MP Stephen Woodworth's motion to study when life begins. Woodworth's private member's motion would set up a special parliamentary committee to examine the current definition of a human being. That definition says a child becomes human when it has fully exited its mother's body.

MPs spent an hour last April debating the motion. Friday was the second allotted hour of debate, with a vote coming next Wednesday.

Woodworth says the definition, found in section 223 of the Criminal Code, is based on a 400-year-old British law that should be updated to reflect modern medical and scientific knowledge.

Section 223 falls under the homicide provisions of the Criminal Code, which define what constitutes homicide — causing the death of a human being.

Fertilized egg 'not a class of people'

Liberal MP Massimo Pacetti and New Democrat MP Irene Mathyssen pointed to Woodworth's admission that he is opposed to abortion, arguing putting limits on the procedure is his end goal.

Woodworth should be up front and ask Parliament to legislate abortion, Pacetti said, instead of trying to set up a committee to study an old law.

Mathyssen said more than 90 per cent of abortions in Canada occur in the first trimester, with no doctor performing abortions past 20 or 21 weeks except for compelling health reasons.

"A fertilized egg is not a class of people," Mathyssen said. "What is absolutely clear — absolutely clear — is that Motion 312 is taking aim at a woman's right to choose and is a direct attack on jurisprudence.

"The right rests solely with the women who choose. No one has the right to interfere. The Supreme Court has upheld that right and so should members of Parliament."

'About fundamental human rights'

Conservative MP Stella Ambler argued in favour of Woodworth's motion, saying the issue already provokes passionate debate among Canadians, and that feelings will only fester if the issue isn't openly discussed.

"Wouldn't it be strange if Parliament even refused to study an update on our 400-year-old ... law?" Ambler said.

"This is about fundamental human rights and about a 400-year-old law, frozen in time."

Conservative MP Mark Warawa said it's important to have a logical debate based on science.

"I think maybe [opponents of the study] are afraid of the truth. What that study would reveal," he said.

MPs first debated the motion last spring, with Conservative Whip Gordon O'Connor giving a speech saying society has moved on and that abortion is an issue to be decided between a woman, her doctor and her family. The NDP and Liberals oppose Woodworth's motion.

NDP House leader Nathan Cullen says there was no question whether his party would have to whip the vote — that is, make MPs vote the way the caucus decides — because they are all opposed to it.

Prime Minister Stephen Harper has repeatedly said Canadians don't want to reopen the debate on abortion. He said last April that he will vote against Woodworth's motion.

Read our liveblog of the debate.