Abelian Sea
o_O
When a sperm and egg get together inside of a woman and join chromosomes, you get this weird little cell. It's weird because unlike all the other cells in the woman's body, this one has different DNA sequences (because while half came from the woman, the other half came from someone else entirely).
As the cell divides into a cluster of cells, that cluster begins to form its own systems. It is physically linked to the woman and recieves nutrients from her, but is, physically, its own organism. Like a tapeworm.
If this organized cluster of cells continues to develop without significant disruption, it will, barring severe internal defects, eventually become a fetus and thence, if the birth doesn't go too badly, an infant.
So if you mean "life" strictly in physical/biological sense, it really does begin at conception. That's the first time you see living cells that are distinct from both parents.
Morality, though, is not so cut and dry. The big question in the abortion issue, to my mind, is "when does that cluster of cells become a person, a bearer of those things we consider 'basic human rights,' specifically the right to not be killed by other people?"
It happens at some point. Once the thing is out breathing air pretty much anyone would consider it murder to kill it. The question is how far back should that concern extend? All the way back to the beginning of its biological life? Is a first-week miscarriage the same as a baby dieing? That seems... off to me, somehow. But it also seems off to consider a kicking little bipedal guy with fingers and toes and a clear nervous system to be nothing more than a biohazard.
Before that point, clearly the woman involved should be perfectly free to have the thing removed like a parasite. After that point, killing it would clearly be immoral under most circumstances, just like killing anyone is immoral under most circumstances.
