It is not a scientific fact that “life begins at conception.” However, genetics is often (wrongly) invoked to support pro-life views. In light of the increasingly tenuous fate of Roe v. Wade, biologists need to keep addressing this misunderstanding. [thread]
DNA does not define a life. An embryo has a different genome than the body carrying it. So do sperm, eggs, and white blood cells. So do the remaining fetal cells in a mother post-birth, which incorporate into her organs. Twins have the same DNA. My future corpse will have my DNA.
In the biological sense, “life” began only once, billions of years ago, and has been continuously transmitted ever since. Colloquially, “life” has many meanings, including a person’s subjective experiences (“My life is hard”). A zygote has no special “life” status in this sense.
Biologists can count distinct organisms, but even we have trouble at the fuzzy borders. Is the largest organism the sequoia General Sherman or the clonal aspen colony Pando? If bacteria-derived mitochondria are part of you, how intimate must bacteria get before they are, too?
Biology does not say when personhood begins. You can choose to believe it happens before or after birth. But don’t try to claim that genetics supports you. If we ever clone a human, I think we’ll all agree that the clone is a distinct person. Genetics has nothing to do with it.
