Modern fertility clinics grow IVF embryos in a petri dish for as long as possible before microscope inspection to discard the failed ones. That's because most fertilized eggs do not survive, often because the egg was deficient at the time of ovulation.
This is quite different from the common view dating from the 1880s that, "From the moment the sperm makes contact with the ovum, all subsequent development to live birth is a fait accompli."6refs
High attrition of fertilized eggs means that it is hard to define a unique moment for the beginning of human life, and that in turn means religious people should find it hard to feel assured when trying to specify time of ensoulment. Stated in Catholic terminology, this new difficulty is that God probably wouldn't endow souls early just to have to turn around and save most of them from limbo.ref
A problem with Roe versus Wade is that, while it fully documents the history of abortion laws, it fails to give the reason so many of them were enacted after 1886 or why they were often reverted in the next century.
1886 is when early science first began to realize that combination of chromosomes from sperm and egg probably constitutes the genetic inheritance of the future individual. Theologians rapidly took this to be evidence of their ideal of a unique event beginning, and therefore theologic timing. This was a new concept for when there is something to protect, so new laws were enacted.
But now with today's evidence that embryos undergo high attrition and that eggs (considering women of all ages) are often deficient, the theologic interpretation becomes more complicated. That is not a job for the US Supreme Court no matter who is elected or who gets appointed.
Paradigm dies hard, and with this one it is not just pro-life advocates, but also pro-choicers who cary on the 1880's view that there is a unique time and event for the beginning of human life. All society knows that everything seems to start with fertilization — except it doesn't.
Nature does the same culling as IVF clinics and more, including after implantation. There is no microscope, though, so the woman often has no clue she carried a failing embryo.
We all come from a fertile egg. Fertilization might then be another step, but does not itself impart life.
An analogy is the balance-wheel clock with a new battery. These usually require a shake to get the balance wheel ticking, but it is the battery and gear mechanism that make the clock work. If the gears aren't meshed right or the battery is low, the clock either won't tick or won't tick very long.
more of the science, but as
a list without interpretation
With Eisenhower, Nixon, Graham and King after World War II the political and religions leaders blended their causes. But since 1980 and spurred with Reagan through Bush II, the influence of religion on politics has become more of a grass roots groundswell, the political part being "Get government off our backs," the religious part being "The beginning of life is at conception" (so abortion is murder). This was a major literal part of the debate in the loss of Kerry to Bush II in 2004. 80% of Americans believe in afterlife,* and large numbers are serious about the timing of ensoulment in the sense of when there is something to protect.
The militant conviction nature of modern American conservatism may have two historic origins - inheritance from the Scottish borderlands peoples who settled in the early frontier, and the Great Awakenings of the born-again Baptist and then Methodist movements in the 18th and 19th centuries. The militant religion of the borderlands peoples, gun in one hand and bible in the other, derived from surviving six hundred years of border wars between the Scottish and British kings.*
The born-again groundswells in the US sprang in large part from the American Constitutional experiment of unfettered religion.*
→Notably, the cores of this past and of the modern theocratic political movement have both been centered in large part on theologic issues of timing, when baptism should occur and when ensoulment is presumed to occur.
Literal quoting has been muted in the US Presidential races since 2004, but the connotations, rectitude and conviction surrounding the assertion that "The beginning of life is at conception" have perhaps come to serve as an extended Great Awakening and a modern attraction glue holding together today's form of frontiersman anti-federalism. Secular law is temporary, ecclesiastical law is forever, and R v W crosses the boundary between the two.
Sociologic history culminating in the frustration of loss to the heinous crime before God of R v W appears to underly the conviction of having to win anti-government conservatism. This is led by angry, dominant, Limbaugh-fan white males and includes: Scalia/Gingrich Supreme Court nominations, anti-trade, hate taxes, hate Clintons, hate ObamaCare, hate abortion, pro-gun, fundamentalist religion and certainty that the entire country is a rotten rigged mess needing change. There is rustbelt economics and wage-spread estrangement here, but this also looks a lot like religious conviction in the mode of borderlands wars inheritance and with the crime of R v W an underlying driver.