And then there is the question, addressed in deliciously-accessible layman’s terms, in the new book Brain Rules by John Medina. An average 30 month old child (2 years, 6 months of age) cannot think symbolically. An average 36 month old child…can.
Put a 30 month old child in a room with a dollhouse. Show that child a tiny plastic dog. Put it under a sofa in the dollhouse. Take the child into a room next door made up to look exactly like the dollhouse room, and ask her to find the “dog”. The child cannot. Do the same with a 36 month old child. The child will run right over to the life-size sofa and find the matching large plastic dog.
This ability to use symbols is apparently (as far as we know) uniquely human. But we would never cut off the age of personhood at 36 months, simply because at this point they begin to exhibit behaviours that are uniquely human.
I understand the use of gestational age to permit/forbid abortion as a convenience and a legal yardstick. I’ve never understood it as a measure of humanity OR personhood. Humans exist on a continuum. A fetus is not a newborn is not an 18 month old who can make simple jokes who is not a 4 year old who can point a stick at you and call it a sword, is not an 18 year old who is supposedly an adult but whose brain won’t finish through through major developmental changes for another 7 years…
But I have spoken to people whose grasp of biology was fundamentally flawed - who did NOT believe life began at conception or even that there was a heartbeat to stop during abortion, or that it could qualify as killing at all…though they had no difficulty with the idea of killing a flatworm or a flea or sprouting seed or the fungus that grows under a toenail. They didn’t want it to be a person or a human, therefore it wasn’t alive at all. And that was just…intellectually pathetic.