Two things, actually, and both stem from arguments that hardcore anti-abortionists want to force on everyone.
The first thing, something that only biologists seem to have thought about, is that production of potential new members of all species vastly outweighs the number who actually survive to maturity. This is normal, in every species of every phylum. In light of this, claiming that the merest beginning of an organism is equivalent to a mature specimen cannot be logically defended.
Did you ever see a large silver maple tree in the fall? The entire tree is covered with little “helicopters”, that fall off and propeller to the ground. Each of them is the seed for a whole new tree. There are millions of them. Depending on the setting, one or two might become seedlings, or maybe none will.
How about sea turtles. Each female lays eggs by the hundreds. Humans or other predators frequently plunder the fresh eggs. When those that do survive hatch, they promptly head for the ocean. Almost all of them don’t make it, becoming lunch for seagulls and other predators. Of the few who make it into the ocean, most are lost to other predators. Only a few make it past the first day, and fewer yet the next month or so.
Very few of the young of any species,
any phylum, survive to maturity.
The situation of animals higher up in the phylumen order is the same, only the odds of survival for individuals are better. For mammals, survival is much more likely because the parents are able to defend their offspring from predators. But survival is not assured, by any means.
Human life is not assured either. Half of all pregnancies abort naturally, early on. Some percentage of the remainder die closer to full term. Some die shortly after birth. Many die within the first year. Human life, precious as it is to each of us, is no more assured of survival than life in other species, so much so that some societies don’t even give a baby a name until a year after birth, when they are more certain he will survive. Such uncertainty is normal for all of nature.
We can readily see that in evolutionary terms humans have been very, very successful. We are in no danger of becoming extinct, which is the primary reason we should be concerned about survival. Several times, though, we were an endangered species, like upland gorillas, polar bears, and a number of other species today. For a while, all the humans alive consisted of a few isolated bands of a thousand or so.
Human life, precious as it is to each of us,
is no more assured of survival
than life in other species.
This also happened with more than one of our predecessor species. If any of our predecessor species had died out without descendant species, homo sapiens would never have entered the picture to begin with. We wouldn’t exist at all. Several other homo species did die out. We can only imagine what they and their descendant species might have been like? The Neanders, our closest relatives, also died out. We actually interbred with Neanders, as shown by some genes we have in common. But we are the survivors. Are we ever! And now we threaten everyone and everything else.
There are already over seven billion of us. We threaten the very biosphere upon which we and all other life depends for survival. Much sooner than we think, there will be ten billion of us, after which the increase in population growth may smooth out. Maybe. But we are already at the limit of what our beautiful blue dot of a planet can support, and showing little sign of responsible behavior toward our only home. We cannot save every single potential human life, and there are already far more of us than there should be. Preservation of every single life has never happened with any species, ever, and it’s very much against nature’s plan.