OTTAWA -- If the abortion debate has been settled in Canada, there was little evidence of that in Parliament on Friday.

MPs were clearly divided as they debated a Conservative MP's motion calling for a study of when human life begins.

NDP MP Irene Mathyssen fears returning to "barbaric days" if a study led a committee to find that a child should be considered a human being before complete birth.

"Such a change in the definition will directly place Canada on the regressive path to banning abortion," Mathyssen said.

Tory MP Stella Ambler encouraged Mathyssen and others not to fear scientific inquiry regardless of where it led.

"If the scientific evidence tells us that our legal definition of who is a human being is wrong, is it right for us to ignore it?" Ambler said. "Why would anyone oppose a respectful dialogue to gather evidence on such an important law?"

Motion M-312 doesn't deal directly with abortion.

Instead, it asks a committee to study several issues, including "what medical evidence exists to demonstrate that a child is or is not a human being before the moment of complete birth."

Mathyssen says she doesn't want to hear from doctors on that question.

"A fertilized egg is not a class of people," she said, without venturing into later stages of fetal development.

Prime Minister Stephen Harper has urged Tories to defeat the motion next Wednesday, likely leading to its defeat.

Tories are still free to vote as they wish, but the NDP has commanded its MPs to vote against M-312.