"Despite many claims to the contrary, life does not begin at conception: It is an unbroken chain that stretches back nearly to the origin of the Earth, 4.6 billion years ago. Nor does human life begin at conception: It is an unbroken chain dating back to the origin of our species, hundreds of thousands of years ago."--Carl Sagan
The ability to clone an individual proves life doesn't begin at conception.
http://www.newscientist.com/article/...y-collide.htmlThe point at which life or personhood begins is not something biology can settle, says David Magnus, co-director of the Stanford Center for Biomedical Ethics, California.
Magnus quotes the example of identical twins who are one entity at the point of fertilisation; not until a few days later do they become separate. They clearly develop into two individuals who have different personalities and patterns of behaviour, even though they share the same DNA. Magnus's assertion raises the question of whether a "soul" assigned at fertilisation would later have to be split.
"Wherever you want to draw the line about where life begins, biology seems to suggest conception is a bad place to do it," Magnus says. If biology tells us anything, it is that nature does not hold the fertilised embryo in particularly high regard. The vast majority of fertilised eggs are discarded naturally, through miscarriage.