how do identical twins factor as evidence for or against the beginning of life?
If we argue (either side) about the time of life beginning, we must recognize that having twins creates two lives out of the same raw material (genetically). They create complexity in the debate for several reasons:
1) They are the same genetic material as each other, yet entirely distinct. Even to the point of having different fingerprints, twins are more than just copies of each other. Clearly there is more to humanity than simple genetic material.
2) Identical twins are not formed until after the egg has been fertilized. Two separate lives are eventually created, but not until a few days into conception. Some pro-lifers argue for conception being the start of life, but I’m not sure that argument holds a lot of water given the exceptionality of twin studies. What do you think?
In fact, twins throw a major wrench into the gears of all philosophical discussion about the nature of humanity (especially discussions of how the physicality of humanity interacts with the non-physical attributes of humanity).
I believe that all life is sacred. It is clearly wrong to dispose of human life through abortion as a means of personal convenience. Some situations are stickier than that, though (danger to the mother, for example). I pray that I never have to make a sticky decision.
Stem cell research should be viewed as a completely different question in my opinion, with a different series of conversations about the different nuances to life. Any answers to these questions must deal with all the evidence.