When Does Life Begin? : 13.7: Cosmos And Culture Can we define when human life begins? At conception? At the embryonic or the fetal stage? The issue, which is at the heart of abortion debates, is far from obvious.

When Does Life Begin?

My wife is about to have a baby. In fact, since I'm writing this on Monday and you are reading it on Wednesday or Thursday, it may have happened already. You will probably be able to guess either way by my answers to comments; or by their absence. In any case, throughout the past 39 weeks, I've been pondering the issue of the beginning of life.

When, exactly, does life begin? I don't mean the beginning of life on Earth, something I do research on, but the beginning of human life, this ultra-controversial topic that triggers wars between pro-life and pro-choice people.

Now, being a physicist and not a medical doctor or a bio-ethicist, I can't claim professional knowledge on the topic. So, instead of coming out with "this is my answer," I will present a few possibilities and let the 13.7 community do its thing. I'm sure you have your own opinions about this.

So, starting from the beginning, conception: We have the joining of the male sperm and the female ovum. The zygote is the result of the biochemical embrace of 46 chromosomes, 23 from each parent. Some could argue, radically, that life starts before fertilization; after all, the male sperm is moving toward the ovum, that is, it has a purpose. Intense signaling is happening in between, as a kind of guiding light, or mating call: "Here, come this way, speed up, will you?!?"

Can we equate life with purpose?

As the sperm fertilizes the ovum, the zygote starts to develop after implantation in the uterine wall. This is what is called a blastocyst and where stem cells can be extracted. An amazing hormonal dance starts. By five weeks there is a neural tube, and the beginnings of the heart and other organs. This is the launching of the embryonic period. The embryo is no bigger than the tip of a pen.

By six weeks, things are happening fast: there is an eye spot, and the beginning of a distinction between upper and lower jaw and even an arm bud. (You can follow the development week by week here.)

The embryo can move its back and neck. Usually, heartbeat can be detected by vaginal ultrasound somewhere between 6 ½ - 7 weeks. The heartbeat may have started around six weeks, although some sources place it even earlier, at around 3 - 4 weeks after conception.

To me, this is a remarkable transition. Here we have this tiny mass of cells wherein a primitive nervous system is already connected to a primitive heart so as to tell it to start doing its job. How exactly does this happen? The first heartbeat is, in a sense, the transition between something with dividing cells to something that has a systemic integration, organs communicating with other organs.

Is it here that human life begins?

By seven weeks, a heart bulge can be distinguished, and also a tailbone and tiny protuberances that will become fingers. By eight weeks, primitive pathways are beginning to connect newly-formed nervous cells, marking the initial development of the brain. The embryo shows everything an adult human shows; this is the beginning of the fetal stage. So, you could argue that now we have this proto-human (or, some will argue, human already) fetus with a pumping heart and a functioning brain. However, her survival is completely dependent on the placenta, i.e., to her connection with her mother.

Another important transition happens when the fetus can survive independently of the mother. But when exactly does that happen? Nowadays, due to remarkable advancements in neonatal medicine, a 26-week premature baby can survive, although with difficulty: serious intervention and an extended stay in the neonatal unit is critical. (Roughly, 80 percent survive.) According to the 2008 National Vital Statistics Report, with data from 2006, only about 6 percent of premature babies are born at less than 28 weeks gestation. We can infer that, as medicine and related technology advances, the survival rates for even earlier term babies will go up. This transition, then, depends on how medically advanced we are.

Finally, we must wonder when consciousness arises in human babies. Is it while still in the womb, at birth or during early childhood?

The question is tricky because it implicitly involves the definition of consciousness, a red herring. If we define consciousness as awareness of one's own state, it will be much later. Even teenagers sometimes seem confused as to why they did or said this or that. (I guess some adults too.) However, a fetus in her third trimester will manifest left and right-hemisphere integration under an EEG, thus displaying the foundation for consciousness. Possibly, the major shock of being born, when the umbilical cord is cut and the baby is forced to breathe and to face a completely different environment, is what jolts the brain into consciousness. At this point the baby is obviously alive, kicking and crying.

In the end, there may not be a single answer to this question since it depends on different interpretations of what life means at different stages of development — which further complicates the issue in general.

At any rate, I'd better get going since I have to get a nursery ready.

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