Arguments for or against the 4 Points of Time for Commencement of a Person

(1) At fertilization (conception in human beings):-
Yes, there is a zygote and then embryo, a new genome, and a strong argument from the potential perspective, to hold it as the commencement of a living human person, to many theologians and ethicists.
BUT

(a) 59-60% of all human embryos conceived (WITHOUT induced abortion) still cannot survive but 'miscarried" before th 8th week of pregnancy 'naturally'.

(b) Science at the moment perhaps still cannot answer for sure that fertilization (conception) as the meeting process of two cells (sperm and ovum) must be the sine qua non (an absolutely indispensable thing) of personhood.

(c) The essential discovery is: In marmoset monkeys, parthenogentic embryos can develop and successfully implant in the uterus. (i.e. need no sperm)

(d) Hence science cannot claim that creation of a new genome as a result of conception must be the absolutely indispensable point of time for commencement of personhood, and cannot even claim that conception is the sine qua non of development of the new individual organism.

(2) Acquisition of an Individual Physical Identity:-
An embryo may develop into twins within 14 days of fertilization (gastrulation), and if that does not happen, then it normally will be growing up into a single person, and so also may be supposed to be the start of personhood. In favour of this view, there are-

(a) scientists doing biomedical research on embryonic stem cells critically take refernce of this very important time slot.

(b) theologians talk about "ensoulment" during the short period  within 12- 14 days of fertilization by the obvious assumption that souls must be unique and separate to individuals including twins, and the time of souls entering the body as a metaphysical event must not be earlier than the first 12 days and not later than the 14th day.

(3) Acquisition of the Human EEG (Brainwave pattern):-
From "neurological" view of life, life only begins on acquisition of brain wave pattern bewteen 24-27 weeks of embryo development. Why?

(a) Actual connection between nervous system and the cerebral nerves only start in significant numbers from 7th month onward.

(b) Such synaptical connections allow communication and then coordination of neural activities  facilitating conscious awareness which to some ethicists, defines  personhood (only from this stage onward), as supported by this neurological view.

(4) Life begins at Birth:-
Why?
(a) Basically, the new genome (DNA) with the embryo alone cannot form the blue print for personhood. as the individual's trait and characteristics.

(b) There must be interaction of genetic DNA with the environmental variables throughout the process of development in the mother's womb that results in human characteristics.

(c) Therefore mother's womb is not a vessel, and the mother's body is a participant to help form the personhood of the baby during the full period of pregancy.

[The above discussions are mainly extracted and/ or paraphrased out from Alton, Althea K's "Staying Within an Understanding Distance"- One Feminist's Scientific and Theological Reflections on Pregnancy and Abortion]

Scientists' View: The Point Where Human Life Begins

According to Gilbert et. al. (2005) Bioethics and the New Embryology:-
There are at least 4 stages of human development that different scientists have asked us to consider as the point at where human life begins-

(a) Fertilization (the acquisition of a complete and novel genome)
(b) Gastrulation (the acquisition of an individual physical entity)
(c) EEG activation (the acquisition of the human-specific electroencephalogram, or brain wave pattern)
(d) The time of, or surrounding, birth (the acquisition of independent breathing and viability outside the mother)

Do classmates agree on the above, and know about the days or weeks after conception for reaching the above stages?

There are other more detailed sub-stages to be discussed later.