Thought of the day: if one zygote divides a little too enthusiastically, it splits from one embryo into two, making monozygotic twin babies. This means that at one point identical twins were actually the same being.
Unless, of course, that one cell wasn't really a being yet.
Oh, the bioethical implications....
“Always recognize that human individuals are ends, and do not use them as means to your end.” Immanuel Kant