To answer this question we must first discuss what life is, as well as what you, as a person, are. For millennia, people have known that life is something special, something unique from inanimate objects. Biology, the study of life, has entranced many minds throughout history, but it wasn’t until the 16th and 17th centuries that the development of the scientific method and the discovery of cells allowed biology to become philosophically and legally reliable.

The cell is the designated smallest unit of life because in many cases it meets 7 main criteria: organized structure, metabolism, growth, response to stimuli, homeostasis, reproductive capability, and adaptation through evolution. Cells are living things that compose all living things on our planet—bacteria, plants, animals, and people. You, as a person, are composed of trillions of these individual lives, and by working together harmoniously, these lives within you each perform specific functions to support your life. According to biology, you are alive, and each cell working to keep you alive is alive.

At the smallest level, it is important to note that life doesn’t actually begin; it continues. Cells can merge together, and cells can divide themselves. But neither of these two events is a clear beginning or end of a particular cell's life. When cells merge or divide, it would be a stretch to say that a “completely new cell” exists. This is why scientists agree that, in general, life continues.

While scientists agree that life continues, it is also a fact of our world that all living things eventually die. Looking at the smallest level of life, we know cells die in four main ways: they can die when squashed by physical forces; they can die when attacked by other cells (or viruses); they can die from senescence (the cell version of old age); and they can die from apoptosis (the cell version of suicide). Within your body, cells die every day, and yet you are still here. This means that your life, as a person, is something beyond the existence of each of your cells.

If you ask a child, “What is a human life?”, he may point at you, or at himself. If you ask a biologist, “What is a human life?”, she may tell you that each living cell within you is a human life because each cell is alive and each cell functions from the instructions of human DNA. You, as a person, are technically composed of trillions of human lives! Believe it or not, human life and personhood are not one and the same. Because the average person does not hold a Ph.D. in both Biology and Philosophy, it's not surprising that people tend to conflate “human”, which is biological, with “person”, which is philosophical. Unfortunately, this causes confusion when people talk about reproductive rights. The confusion causes frustration, frustration causes anger, and anger between two groups of people leads to trouble. 

The truth is that the concept of personhood isn't biological. It's philosophical. The video below can give you a crash course on the philosophy of personhood. The narrator, Hank (co-founder of the educational channel Crash Course), clearly and impartially describes the difference between human life and personhood . . . hear for yourself by watching the video below.


To recap, definitions of personhood reviewed by Hank are Noonan’s genetic criterion, Warren’s 5 criteria, the social criterion, Singer’s sentience, and the gradient theory of personhood. But none of these specific definitions of personhood have been able to settle the tension between Pro-Life and Pro-Choice groups. So, Respect People offers you a different definition.

After watching Hank's Crash Course on Personhood, you should understand that human life and personhood are distinct concepts. While each living cell within you is a human life, only you, as the sum of the coordinated function of those human lives, are a human person. This means that the life of any one of your cells and your life, as a person, are two different things. For example, have you ever considered how your future death is not simultaneously the death of all the cells in your body? After your death, cells within the body you left behind can live for days, with some cells living for more than two-weeks after you're gone, until they run out of energy to consume, since you are no longer there to control that body and eat to provide those cells with nutrients. If you were an organ donor, some of the cells with your DNA will live for much longer than two weeks after your passing. Indeed, cells with your exact DNA, that used to be a part of you, can live on within, reproduce within, and be a part of another person. You need your cells, but your cells don't necessarily need you! 

Here's the point: If the end of your life is not congruent to the death of all cells with your DNA, then it is reasonable to consider that the beginning of your life is also not congruent to the rise of new cellular life with your DNA. Therefore, to answer the question "When did your life begin?", you must ask yourself what distinguishes your life from the trillions of cellular lives that support you?

We have thought hard about this question, and we arrived at an answer: While we and our cells both meet the 7 criteria for biological life, we, as people, meet 2 additional criteria: we can think thoughts and feel emotions! Thus, Respect People defines a person as a life form that meets the 7 criteria of life (organized structure, metabolism, growth, response to stimuli, homeostasis, reproductive capability, and adaptation through evolution) plus 2 more criteria specific to people (the ability to think thoughts and feel emotions) for a total of 9 criteria. 

After hearing these 9 criteria for the first time, many people ask, "How do the 9 criteria for personhood measure up to a comatose person?" The answer is simple. A comatose person may not be able to communicate, but unless the person is medically determined brain dead, they still have the ability to think thoughts and feel emotions. Without a doubt, there is a difference between having an ability and using it. There is also a difference between having an ability and remembering using that ability. For example, we do not remember all of our thoughts and emotions from when we were three years old, but the fact that we don't remember does not negate that fact that we did have those abilities. Likewise, a person who experienced a coma may not remember many thoughts or emotions from the time they were comatose, but not remembering is not proof that thoughts were not thought and emotions were not felt. The bottom line is that all people have the ability to think thoughts and feel emotions. If a living thing can neither think thoughts nor feel emotions, it is not a person.

The process of differentiating people from other forms of life can be simplified by acknowledging that the ability to think thoughts and feel emotions occurs from within one specific organ: the brain. Your brain, a magnificent organ, is what permits your life to be extraordinary compared to cellular life. When your brain ceases to function, you are gone. Likewise, when your brain gained functionality, you became you.

A standard of brain functionality is the most reasonable option we have today to define personhood scientifically, philosophically, and legally.  Five common but less reasonable depictions of the start of personhood are:



The Quickening



If you’d like, click each term above to learn more.

From a purely philosophical perspective, fertilization, heartbeats, and the quickening are each too problematic to be agreeable markers for the beginning of personhood (Click the bolded terms above for further explanation).

Viability and birth, on the other hand, are accepted markers of personhood in law. Viability is seen in law such as in Roe v. Wade, and birth is seen in law such as in Section 1 of Amendment 14 in the United States Constitution, which grants people born in the United States the right to life, liberty, and property.

The issue with viability and birth as markers of personhood for rights and protections is that people worry about the suffering of other people, and accordingly, people worry about the potential suffering of unborn fetuses before and after viability. If you can think thoughts and feel emotions, you can suffer. Secularly, we know that after person's life ends, they can no longer suffer. In parallel, it's philosophically fair to say a person's life begins when a collective of human cellular life develops the ability to think thoughts, feel emotions, and suffer.


The majority of doctors and scientists agree that the point at which a developing human body can suffer is between 23-27 weeks gestation, when important thalamocortical fibers form.  For example, the American College of Obstetricians and Gynecologists (ACOG) says the ability to feel pain arises in a developing fetal body by the third trimester, which is about 27 weeks gestation. And, in describing consciousness, Dr. Christof Koch, a chief scientist at the Allen Institute for Brain Science, writes, “Consciousness requires a sophisticated network of highly interconnected components, nerve cells. Its physical substrate, the thalamo-cortical complex that provides consciousness with its highly elaborate content, begins to be in place between the 24th and 28th week of gestation" (When Does Consciousness Arise in Human Babies?, published September 1st, 2009 in the Scientific American).

Overall, the science of understanding when a fetal brain can feel pain is multifaceted but not so terribly complicated that the average person cannot get the gist. The basics to understand are that a fetus can for certain suffer by the 30th week of gestation and that the earliest a fetus could suffer, though it is unlikely, is the 23rd week of gestation, because this is when critical thalamocortical fibers in the brain begin to form. To learn more about fetuses' ability to suffer, review these two articles.

If, based on new evidence, the scientific community ever updates the point at which a new human mind exists, then the answer to this first question will be updated, but for now, the secular answer to "When did your life begin?" is between 23-27 weeks of gestation.