In science, the term "conception" commonly refers to fertilization. But among bioethicists, conception is sometimes defined as implantation or even "the point at which human life begins". Because of the imprecise meaning of the term, it has served as the fulcrum for semantic arguments within the abortion debate. The typical usage one encounters among anti-choice proponents is that
life begins at conception. The statement is often made with complete confidence as though it's the uncontroversial scientific truth.
It does sound good, hard to argue against, right? Nope, it's a right-wing myth, as accurate scientifically as 'there is no evidence for global warming' and 'Intelligent Design is a scientific theory'. Developmental/evolutionary biology Professor PZ Myers, who happens to study embryos for a living, gives some insight:
[Link] Developmentally speaking, fertilization is one transition state among many. It's a major bottleneck and an incredibly wasteful process--the overwhelming majority of gametes fail to fuse--but even when fertilization occurs, Nature is quite cavalier about throwing the whole thing out and requiring us to start again. Other major events in which an error can negate all prior processes are implantation, gastrulation, neurulation, birth, and learning to drive. It's awfully silly to privilege one event among many as the sole source of humanity, I would think; if it's mere priority that focuses interest on fertilization, the two meiotic divisions that produce the gametes came first, and that's also a delicate and critical process. Perhaps you should worship the gonad rather than fertilization...?
Does 'life' begin at conception? Well, obviously the egg and the sperm are alive, so it depends on which cell's life we're focusing on and which is ignored. What happens when the one lucky sperm among millions reaches an egg first? What are the steps that can go right or wrong after that? What does the term conception cover?
Some bullet points:
- The head of the sperm binds to the outer coating of the egg
- The tip of the sperm head then releases enzymes that chemically burn a hole through the outer layer of the egg
- The sperm head moves into the opening thus created and binds to the plasma membrane further inside of the egg
- The membrane around the head of the sperm and the membrane around the egg plasma fuse
- The inner contents of the sperm, including the genetic components, are delivered into the cytosol of the egg
- The egg plasma releases substances which thicken the outer wall, preventing the other zillion horny sperm that arrived slightly late from getting in on the action
- The nucleus of what's left of the lucky sperm swells, forming a male pronucleus
- At the same time, the egg completes meiosis II forming a second polar body and the female pronucleus
- The male and female pronuclei move toward each other and their nuclear membranes bind, fuse, and dissolve
- The centriole in the sperm remnant replicates, and a joint structure called a spindle is formed, where the first full set of diploid chromosomes begins to assemble
Based on extrapolation, the sperm and the egg will not make it through the above steps between 25 and 50 percent of the time. After the formation of the first diploid set, the fertilized egg, now called a zygote, is ready for its first regular divisions to begin. After about seven or eight divisions, when the zygote is made up of around one-hundred identical cells, a differential starts appearing between the cells that will become the fetus and those that will become the placenta. This stage is called a
blastula. A few more fertilized eggs will be lost during the change from a single celled zygote to the blastula.
But wait! We're not home free, not by a long shot. The blastula has to successfully implant in the uterine wall and avoid being rejected as the proto-placenta begins growing into the uterus. Perhaps another 25 to 50 percent will be lost in that process.
Note: If anyone thinks I'm beings overly technical above, trying to dazzle the pro-lifer with physiological terms or whatnot, I'll bet twenty bucks there are biologists out there reading this who are groaning in pain at the gross oversimplifications. Because I just crammed about 4 semesters of advanced molecular biology and early fetal development into a few pitiful sentences.
Oh and by the way, speaking of science and genetics: Fellas, the last time abortion was illegal and birth control virtually non-existent, there was no such thing as genetic paternity testing and certainly no court mandated child-support based on it. Keep that in mind if you think restricting abortion or birth control isn't going to affect your life. But look on the bright side; whether it's an affair, a girlfriend, or just a little out of town fling on a business trip or on Spring Break; sure, it might ruin your life or your marriage, you might have to drop out of college, and it won't do your paycheck any good to have a big fat deduction taken out before you get your hands on it. But hey, you might like being an unexpected daddy!
Anyway, the point is that less than half of all the blind dates between sperm and egg make it successfully through the above steps. And that's a conservative estimate. In most cases when the sperm strikes the egg's surface, the sperm dies, the egg dies, and/or whatever stage the embryo or pre-embryo is in, dies. No doubt this is far beyond the format constraints of talk radio or cable news (And significantly above the heads of the proudly ignorant right-wing ideologues). So for the soundbite answer, it would be perfectly accurate to respond to the question of "What happens at conception", to say, "Usually, death".