| Now if a human life begins at conception, we need an explanation for the phenomena of twinning and recombination. Twinning is the division of one conceptus into two, and recombination is the opposite: the reuniting of two conceptuses into one. Each phenomenon can happen within the first two weeks of an embryo’s life.
This is possible because of something called cellular totipotency. The early embryo consists of totipotent cells. A totipotent cell has the ability to develop into a specific part of the organism or to become a new organism. This makes perfect sense considering that one cell must develop into an organism of a vast number of cells. The first cells must be versatile, and later cells must be more specific.
Here’s the question. If the first cell can transform into two beings, and if two cells can merge into one, how can we call one of them an individual human life?
We can do so by recognizing that the one that divides into two had a predisposition for dividing into two so that both souls were there at the beginning. We can also see that the one that divides into two and recombines into one again already had a predisposition for it, so that the one soul never divided into two and merged back into one. Francis J. Beckwith mentions evidence that “monozygotic twinning has a genetic cause (hence, it runs in certain families). It seems, therefore, that some zygotes have a basic duality prior to their splitting – an intrinsically directed potential that is not present in most other zygotes.” In other words, only some individuals have the ability to twin or recombine.
Beckwith continues, “Suppose, however, that the early embryo were to possess an intrinsically directed potential for twinning that may be triggered by some external stimulus. This would only mean that the human being, early in its existence, possesses a present capacity (i.e., twinning) that becomes latent after a certain level of development, just as some latent capabilities become present later in its existence (e.g., the ability to do algebra).”
In other words, we need not rule out environmental factors. It is still the cell itself that has the genetic encoding that enables it to twin or recombine. Blind chance on the other hand is never a factor. Beckwith points to Edwin Hui who said, “the two beings that emerge as twins are in actuality two from conception, although in a ‘latent’ form.”