Question: When does life begin?
If by life you mean “human life,” this is a very complicated question that has no real answer. What you’re about to read is a combination of scientific fact and my respective interpretation of it.
Fertilization is the point at which two haploid gametes merge to become a diploid cell. This new diploid cell, or zygote, contains all the genetic material it needs to develop into a mature organism. Fertilized eggs are indeed considered living cells, so with that said, it’s not entirely unreasonable for one to infer that some sort of “life” begins there. However, all zygotes previously existed as two individual living gametes - split as an egg and a sperm before fertilization. Scientifically speaking, egg and sperm cells are living cells, so they are alive. They are not, however, in themselves humans, and thus do not constitute “human life.”
Why not? The capacity to develop into something does not constitute its existence as that thing. In biology, there are cells called “totipotent stem cells” that, given the right conditions, can develop into individual organisms. Totipotency is a complicated concept, but an example of it is cutting a piece of a plant, replanting it, and watching it grow into a brand new organism (no seed involved). While the totipotent cells involved helped make the plant cutting develop into an individual, they in themselves are not individual plants - it’s their product that is. Now, back to the zygote: a fertilized egg is classified as a totipotent stem cell, and I would say that it is no more a human being than a regular, single stem cell in your brain is your “other” brain.
That may be a bit confusing, so let me use another example – monozygotic, or identical twins. Following fertilization of an egg, there is about a 16 day period where the zygote retains its totipotency. During this time frame, if the zygote splits into two, you result in identical twins. If you classify the zygote as a human being, or introduce individuality or the concept of a “soul” to the zygote from the moment of fertilization, that would mean that a human being can be split in two, and that identical twins are the same human being. Life doesn’t work that way - it’s complicated, versatile, and most importantly, a scientific concept.
Life may seem like a magical phenomenon, but while truly beautiful, it is not magic. Two or three years ago, scientists were able to create the first self-replicating synthetic life form. That’s right – we are now in an age where humans are able to create life. As technology progresses, it is very likely that a combination of neuroscience and molecular genetics will be able to map out literally everything that you are as a human being. We’re getting to the point where there is no room for magic.
Several paragraphs later, we return to your original question. I believe that the question, “When does life begin?” is scientifically, an arbitrary question in itself – any satisfying answer would have to be philosophical in nature. Based on current biology, there is no singular definition of life - Life is more of a characteristic. The progression of a zygote into a human being is a developmental process, and there is no one point in development where we can label a blastocyst or embryo, or even fetus as an actual human being. What we can do, however, is use tangible markers such as when a fetus’ heart starts beating, or its nervous system begins to develop, or it first begins responding to external stimuli to really get a sense of what the life form really is.
Image source: The Progressive Pulse