To conclude, I would be interested in hearing what you have to say to my conjoined twins scenario. A single embryo at some point splits, but not completely enough to have it become a separate organism (or at least, not permanently). It then develops into identical twins who are (say) conjoined at the hips (they share the same pair of legs). If our only 'moral ingredients' are biological, then this is only one human being. From my perspective however, since personhood depends on relevant neural structure, I would say we have two human beings (in the moral sense--one in the biological sense) since there are two brains. So as I understand your perspective, destroying said twins before birth and cell splitting would be one murder, and destroying said twins after birth would be two murders (but why two if your only criterion is biologically human genetic code?).If I understand Daniel's point correctly, he believes that conjoined twins are biologically one human being that happens to possess two separate brains, thus being considered two morally relevant human persons.
From a purely biological standpoint, Daniel is incorrect. Conjoined twins are two separate human organisms that have been fused together during the process of embryogenesis. Here is a citation in the medical literature which confirms this:
A review of over 1,800 publications concerning the embryology and pathologic anatomy of conjoined twins provides convincing evidence that they all result from the secondary union of two originally separate monovular embryonic discs.We could conceivably reproduce conjoined twins surgically by taking two monozygotic twins after birth, and surgically fusing their hips together. In this case, would anyone claim that there is only one human organism? Clearly not. A similar mechanism is responsible for conjoined twins, although it occurs at about day 14 post fertilization in humans. We consider conjoined twins as two individual human organisms, because they are two individual human organisms.
To address the moral question, it would be wrong to behead one of the conjoined twins for the same reason it would be wrong to stab one in the heart. The result of the action would be the death of a human organism, albeit one that is connected to another human organism. That is what makes the action wrong.
Lastly, when Daniel speaks of a "biologically human genetic code" as conveying human value, he needs to be careful to avoid a straw man. The pro-life view as expressed here is that every human being, or living organism of the species Homo Sapiens, has intrinsic value and should not be intentionally killed without adequate reason (the language I am using is purposefully unambiguous). It is not the mere presence of a human genetic code, but the use of that code by an organism of our species.