When does life begin?

The unborn child responds to sensory input as early as seven weeks (gestational age). All of the organ systems of the developing human demonstrate function simultaneously with the appearance of the anatomical structure. By 10 weeks, the human embryo has well-developed organ systems and most of the anatomy can be named with the same nomenclature that we use in adults. The brain has been growing rapidly and will continue to develop as the baby grows, moves, and experiences the sensory input of the environment surrounding it. There is no point in development in which the structure exists without function.

"Q&A with the Scholars: The Science of Fetal Pain," Dr. Sheila Page, DO

Science agrees on this point: Life begins at conception.¹Here are five vital signs of life in the womb to consider:²

Heartbeat: Modern technology can detect the baby's heart 18 days after conception — about 4 days after most women miss a period and begin to suspect they are pregnant. It can be seen to beat by day 22. Between conception and birth, the heart beats approximately 54 million times!
Brain waves: By 6 weeks and 2 days from conception, signals from the brain can be detected.
Independent movement: Although a pregnant woman does not feel movement for at least another 8-10 weeks, the embryo begins to spontaneously move between 5-6 weeks.
Senses: By 8 weeks and 2 days, touching the embryo will elicit squinting, jaw movement, grasping motions, and toe pointing.
Breathing: The embryo can hiccup by 7 weeks. The diaphragm muscle is completely formed by 8 weeks and intermittent breathing motions begin.

Sources:

1. Keith Moore, T.V.N. Persaud, and Mark Torchia; The Developing Human, 10th Edition: Clinically Oriented Embryology, (Saunders), 2015: “Human development is a continuous process that begins when an oocyte from a female is fertilized by a sperm from a male.” And, “Human development begins at fertilization when a sperm fuses with an oocyte to form a single cell, the zygote.”

2. "Prenatal Summary," The Endowment for Human Development,http://www.ehd.org/prenatal-summary.php, accessed 3/9/2017. See also the "Prenatal Timeline."

See also "Q&A with the Scholars: Science and the Beginning of Human Life," Charlotte Lozier Institute interview with Maureen Condic, PhD, Associate Professor of Neurobiology and Anatomy at the University of Utah, accessed 3/9/2017. And "Why the human zygote is an organism (and why it matters)," National Right to Life News Today, March 20, 2012, accessed 3/9/2017: "From the moment of sperm-egg fusion, a human zygote acts as a complete whole, with all the parts of the zygote interacting in an orchestrated fashion to generate the structures and relationships required for the zygote to continue developing towards its mature state."

It's alive, but is it a person?

Many more milestones of life could be noted here, but the bottom line is, once a human egg is fertilized by sperm, a new human being has come into existence. All information concerning the child's sex, hair color, eye color, and much more is present from the very beginning.

If the newly formed being is not human life, what is it? And how should it be treated?

Some people acknowledge that it may be human life, but say it is not yet a person. They get stuck on terms like zygote or embryo or fetus, but those are just stages of life, like infant or toddler or teenager. What are the signs of personhood?

God, the Author of all life, should have something to say about His creation, and He does! In Psalm 139:13-16, David responds with wonder at how well God knows him:

You created my inmost being;
you knit me together in my mother's womb.
I praise you because I am fearfully and wonderfully made;
your works are wonderful, I know that full well.
My frame was not hidden from you
when I was made in the secret place. . . . your eyes saw my unformed body.
All the days ordained for me were written in your book before one of them came to be.

God's knowledge of us before birth means that we are important to Him even then, because we are made in His image (Genesis 1:26-27). God's Son Jesus was "made in human likeness" (Philippians 2:7), starting out his ministry on Earth as an embryo in the womb of Mary. Then He died on the cross to end our separation from God that was caused by our sin. Romans 5:8 says:

God demonstrates his own love for us in this:
While we were still sinners, Christ died for us.

Because God made us, knows all about us, and loves us, He alone has the right to determine the boundaries of our lives, including the end. From the moment of conception, every human being has worth — is a person — because we bear His image. This is why it is immoral to end the life of another human being, even at its earliest stages. Learn more about what the Bible says about life in the womb.