When does life begin?

I was driving back from a Louisville Area Skeptic‘s meetup and saw a billboard saying that a fetus has a heartbeat at 21 days.

Was that correct? More importantly, did it mean anything useful?

It’s not quite correct. Heart cells develop about 20 days after conception, and the fetal “heartbeat” is first detectable at about 22 – 23 days after conception, so 21 days is a bit early. Since pregnancy weeks (gestational age) are counted from the beginning of your last period (or 14 days before conception), we need to add two weeks to the above time-line if we are to use that framework. Let’s stick with time from conception.

Is it an actual heart?

No. It is a small amalgamation of cardiac muscle tissue. Cardiac cells beat rhythmically on their own, and in concert if they are in contact with each other. In the first week after heart cells develop (around 4 weeks post conception), they are a bulge, a tube-like formation. Between six and seven weeks after conception, the heart can pump a blood-like fluid through tubes like blood vessels.

Is that really useful in determining when life begins? Thats the wrong question altogether. The right question is “What is life?”

Life requires certain features. First of which is the capacity to reproduce, and not necessarily sexually. Your body has to replace old or damaged cells, heal wounds, grow. Second, life has to be able to carry information that can be passed on to the next generation of cells. This hereditary information is carried by cells in their DNA. Third, life has to be able to use energy to drive a metabolism. This means making proteins, burning sugars and fats or storing the same, reproducing, etc and to keep those reactions going. Finally, life must be able to respond and interact with its environment in some manner. Bacteria swim towards food, light or away from things that would kill the bacteria. Fungi grow towards food. Plants grow towards a source of light. Even quasi-alive viruses can interact with their environment as they come into contact with the appropriate molecules for their receptors to interact with. Flowing from these four functions of life is the process of evolution by natural selection.

Any one of our cells is alive, but without the whole body, they cannot meaningfully reproduce. Not into a whole new organism, not into a whole new human. You need to combine an egg cell and a sperm cell to form a fertilized egg in order to begin the process of cell division that produces a new human.

Does this mean that life begins at conception? Again, not quite. Sperm cells are alive. Egg cells are alive. Sperm cells and egg cells have all the features of life. Sperm and egg cells combined to form a fertilized egg that can divide.

Egg cells and sperm cells are alive.

Life doesn’t begin at conception, not at least, life as defined by science. Life continues.

When people ask when life begins, they are asking a metaphysical question. When does the soul enter the body?

We can’t use an instrument to detect the presence of a soul, let alone determine the moment of ensoulment. The soul is not a concept that can meaningfully be examined by science, no matter how strongly you believe in it. Until someone develops a device or test that can reliably detect a soul, science can’t consider this as a valid question.

Don’t ask a scientist if you are asking for an answer that helps you win a political or religious argument. The answer you get won’t always be the one you want.