Biologically speaking, a human being is an organism of the species Homo sapiens.
A human zygote is an organism of the species Homo sapiens:
A human embryo is an organism of the species Homo sapiens:
Embryo: An organism in the earliest stage of development; in a man, from the time of conception to the end of the second month in the uterus.
– Dox, Ida G. et al. The Harper Collins Illustrated Medical Dictionary. New York: Harper Perennial, 1993, p. 146
A human fetus is an organism of the species Homo sapiens:
To describe an embryo or fetus scientifically and factually, one would say that a living embryo or fetus in utero is a developing organism of the species Homo Sapiens which may become a self-sustaining member of the species if no organic or environmental incident interrupts its gestation.
This is a fact upon which science is settled.
Physicians, biologists, and other scientists agree that conception marks the beginning of the life of a human being – a being that is alive and is a member of the human species. There is overwhelming agreement on this point in countless medical, biological, and scientific writings.
– Report, Subcommittee on Separation of Powers to Senate Judiciary Committee S-158, 97th Congress, 1st Session 1981, 7.
Whether or not human being is entitled to human rights — in other words, when a human being becomes a person — is a philosophical argument that is certainly up for debate.
I think that all human beings are persons, as all arguments otherwise rely on arbitrary, subjective criteria that would also deny human rights to certain born persons — but I acknowledge that the philosophical concept of personhood is not something that can be proved, objectively, by science.
However, we CAN determine objectively, with scientific research, the criteria for what constitutes an organism of the species Homo sapiens.
A human being meets that criteria at all stages of his or her life, from conception to death.
Just in the past few days alone, I have witnessed abortion rights supporters make the following arguments:
“Fetuses aren’t human beings any more than sperm and eggs are human beings.” False. Spermatozoa and ova are human haploid gametes, not organisms.
“Embryos/Fetuses aren’t human beings because they aren’t sentient.” False. Sentience is a philosophical concept, not a scientific one, and is not included in scientific criteria for what constitutes an organism.
“Embryos/Fetuses aren’t human beings, they are parasites.” False. Parasites must, by definition, be of a different species than their host. Embryos/fetuses are of the species Homo sapiens, just like their parents, thus they are not parasites.
“Embryos/Fetuses aren’t human beings because they can’t live outside the womb.” False. Level of dependence on one’s parents is not included in scientific criteria for what constitutes an organism.
And many more arguments along the same vein.
Abortion rights supporters who try to deny that human zygotes, embryos, and fetuses are organisms of the species Homo sapiens are similar to members of the Flat Earth Society. They are denying objective scientific fact.