by Doctor Science
Shannon Dingle posted I'm Pro-Life and I'm Voting for Hillary, because she thinks "pro-life policies" should mean support for all kinds of children and parents, not just opposition to abortion.
It's a very thoughtful, nuanced post in general, but includes this statement:
I believe life begins scientifically at the moment of conception when new and unique DNA is created when the egg and sperm meet. Except in rare cases, like ectopic pregnancies and other circumstances in which the zygote can't become a fetus and then a born baby, life will continue from that point unless interrupted.
I've heard something very similar from many "pro-lifers", including some here. The problem with this paragraph is that it claims to be about "science", but is made up of errors or falsehoods.
1. "Scientifically" life does not begin, it is transmitted. There is no non-living link in human reproduction. The scientific answer to "When does life begin?" is "Three billion years ago." For "When does human life begin?" the answer is "About 100,000 years ago."
2. Not all humans have new and unique DNA: identical twins are people, too. The process of splitting one zygote into twins is not instantaneous, and frequently the identical embryos recombine to form a single individual. At what point do you say "there are two human lives here"? If they recombine (or one absorbs the other) after that point, has there been a death? (I wrote about this point and the next 4 years ago, in A single cell is not a person: the problem of twins, but because I am basing my opinions on science, they've changed a bit since then.)
3. Conversely, some individual humans are chimeras: they contain two different sets of "new and unique DNA", when two distinct embryos (in your thinking, two distinct human lives) have merged in utero. If you start with 2 human lives and end up with one individual, does this mean that one of those human lives ended? Which one?
4. The statement that life will continue from the point of conception to birth "except in rare cases" is false. On the contrary, it's been estimated that only 30% of human conceptions progress to live birth. About 25-30% never make it to implantation (which is the start of pregnancy), another 30% die during the first week or so, 10-15% are recognized as miscarriages, and 1% are stillbirths.
It turns out that a large percentage of human zygotes are not capable of developing to the point of birth because they don't have a "clean" set of chromosomes. This is extremely surprising, and so far unexplained--though obviously a hot topic for research. It's surprising because in other well-studied mammals (mice, for instance), 90% or more of zygotes are good to go. It's also surprising because conception and early embryo formation are "mission-critical" for living creatures. Natural selection will act most strongly, random mutations won't be tolerated, and we expect the biochemistry to be very conservative and slow to change.
And yet, human reproduction seems to be *incredibly* buggy, much more so than for chimpanzees. My evolutionary-biologist instincts suspect this didn't evolve via natural selection, but is a mistake solidified by inbreeding during a severe population bottleneck at some point well before the evolution of Homo sapiens: from 200,000 years ago back to maybe 1.5 million y.a.
Regardless of cause, right now the reality is that most human zygotes cannot lead to a live birth. They're all human and alive, but only a minority of them are capable of becoming a human person. Most are not "babies", even potentially.
5. Saying "life will continue from that point unless interrupted". No, without the active support of a human uterus the death rate for human embryos is 100%. An embryo's life doesn't just "continue", it needs ongoing contributions from the mother to stay alive.
Even on the biological level, these contributions aren't automatic. It's becoming clear that the uterus isn't just an accepting and supportive environment for embryos, it's a testing ground. The uterus chooses (there's that word again!) which embryos are worth growing, and aborts the rest. That's why so many human embryos die in the first week or so after implantation: some are too buggy to make it any further and die on their own, but others are killed by the lining of the uterus.
It's been plausibly suggested that this is why humans menstruate--unlike the other great apes and almost all other mammals, which thriftily re-absorb the uterine lining instead. Costly, messy menstruation is worth it for humans, to clean out defective embryos that have embedded themselves in the uterine lining. It's the natural equivalent of a post-miscarriage D&C each cycle.
Science-based arguments can be made for putting "the start of respectable human life" at a number of different times during development: conception, heartbeat, movement or "quickening" (traditional), brain formation, brain development, birth (another traditional point), etc. Some of these arguments may well be stronger than the ones for conception. And that's aside from the point that Christians should really be talking about immortal souls, not biological lives, and are using "when life begins" as a kind of rhetorical stalking-horse for "ensoulment", which is clearly not a scientific term.
The current "pro-life" movement doesn't date respectable human life from conception because that's scientifically irreproachable (it's not). They *chose* that point for non-scientific reasons, then picked the science to support it. It's dishonest, and follows a tradition of ignorance and bullshiting in the movement. I'm using "bullshit" in philosopher Harry Frankfurt's sense, to mean that they're not consciously lying, they just don't care about the truth.
 I first heard (read) this formulation in the 1980s, in a report about a scientist testifying at a Congressional hearing. I can't find the reference, though.
 I'm using "respectable" to mean "worthy of respect similar to that toward a person". Because I can.
It's strikingly difficult to find a Goddess of Miscarriage in any culture. I can't believe that women didn't pray to *someone* in their religious pantheons: prayer for solace after a miscarriage, prayer to avert another one, and prayer to have one, when a woman was pregnant and didn't want to be. I'm betting that lack of evidence here is because written records come from men, and miscarriage rituals fell behind a heavy veil of Women's Mysteries. Coatlicue is just one possible nominee.