1. Embryos lack rationality, capacity for relationship etc (neural crest first appears at 10 days etc)
Rejoinder: The value of a human being does not consist in its capacities or attributes but in the fact that it is human. We do not even have to be known by God, it is sufficient that he knows us. The value of an embryo is bestowed by grace.
2. The high mortality of early embryos (40-70% don't reach maturity).
Rejoinder: The value of human beings is not contingent on their survival rates, and even if survival rates are low this does not mean that we may act to end their lives prematurely.
3. Many embryos are abnormal and abort spontaneously.
Rejoinder: The value of human beings is not contingent on their level of normality, and even if they are abnormal this does not justify us killing them.
4. Sperm and ova are alive but that does not make them human, so why should an embryo be human?
Rejoinder: The embryo is a genetically distinct human being; already with a unique genotype and the ability to grow. Sperm and ovum are not.
5. Two sperm may form an 'organism' as in hydatidiform mole.
Rejoinder: A hydatidiform mole is not a human being since it not formed from the union of a male and female but rather two male gametes.
6. Conception as a process is not complete until the first cell division (or implantation)
Rejoinder: Yes, but it begins at fertilisation, and we should not interrupt the process at any point once it has begun. 'Life' is a process but that does not justify us ending it.
7. Not all tissue derived from the fertilised egg ends up in the embryo (ie some is yolk sac etc)
Rejoinder: Yes, but this makes the embryo something more than a human being rather than something less. We should surely then show the conceptus extra respect in case we damage any part of it which is destined to be part of the complete organism. (cf Shylock's task)
8. Twinning. If the fertilised egg can grow into two individuals was the original pre-split conceptus a third individual or did one of the lives begin after fertilisation? Since it is impossible to conceive of two souls residing in one embryo it cannot be possible.
Rejoinder: The fact that we cannot resolve the mystery does not mean that we can therefore conclude that the embryo has no value. Christian theology has no difficulty concluding that three persons co-exist in one Godhead so why not two persons in one body?
9. The image of God was lost at the fall.
Rejoinder: If so then why does the command not to kill (Gn 9:6) (which makes reference to the image of God) come after the fall?
10. The soul enters the body after the time of fertilisation
Rejoinder: The Bible does not say this at any point; and soul-body dualism owes more to Greek cosmology than biblical theology. Man has a body and is a soul, rather than the other way round.
11. We don't treat embryos like human beings (eg don't baptise them, mourn their loss etc)
Rejoinder: Their value is not dependent on what we think of them but what God thinks. How would one baptise embryos anyway? And isn't that an Anglican problem anyway?
12. We don't recognise embryos as human because we use IUCDs etc
Rejoinder: Perhaps we should change our behaviour!