The reason religion is so powerful

[brewer]

No one is arguing that a fertilized egg isn't biologically human with the potential to eventually develop into a person, the argument is that there is no evidence that it is a person.

Personhood appears to be a legal term. You don't find evidence of personhood, you have to legally describe it. Perhaps no different from legal adulthood being 18+.

In biology, human is the category—that's our species. And embryo, fetus, infant, childhood, adolescence, adulthood, late adulthood—these are all our developmental stages. That's all there is to it.

And the embryos that don't implant and get flushed, what human rights should they have?