Okay, but what is conception, precisely? Why does the Church define fertilization as “the penetration of sperm into the oocyte” and not when “the chromosomes in the male and female pronuclei are actually joined”?
For years, conception and fertilization had the exact same definition. That’s where the Church stands. Therefore, the Church’s answer to your question of what is conception precisely is penetration/fusion of sperm & oocyte. Once the oocyte is penetrated, fundamental changes in it begin a process that cannot be un-done. Science has gone a bit further & defined when the male & female pronuclei are joined as fertilization (some scientists argue about conception’s timing). However, basically the Church is agreeing w/ science, but not using the same terms. The Church presumes/assumes that the male & female pronuclei are going to join b/c that is the next step in the process of forming a fully formed human being. I’m not sure of the statistics (if there are any), but I’m going to hazard a guess that in
most instances the male & female pronuclei fuse as long as their isn’t a serious defect in either (which probably would indicate that penetration wouldn’t occur either).
Here’s a secular site about fertilization from Colorado State
arbl.cvmbs.colostate.edu/hbooks/pathphys/reprod/fert/fert.html As it indicates, fertilization is not a one-step process. In this discussion, the zona pellucida is part of the egg - in a way it is the protective covering similar to an egg-shell, but much softer & permeable. This discussion actually defines fertilization as the Church does. It indicates that fusion of pronuclei is a post-fertilization event.
This is another source - an IVF resource - that indicates that your scientific definition is not commonly used. Instead fusion of the pronuclei is a post-fertilization event.
umm.edu/ency/article/007279.htm However, it is not as clear about the definition as the previous link.
This link - an NCBI article - groups both the Church’s definition and your scientific definition as the parts of the same process it seems.
ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.section.3738 However, they aren’t specific either. It can be interpretted either way.
The short answer to your question is that the Church’s definition goes along with science’s definition. Science, by its very nature in this sort of thing, is just a bit more specific. The Church relies on science to guide and educate. The Church is concerned w/ the ethics & morality of the science.
