Last week I was challenged to a debate about when life begins. I knew the answer was tricky from a scientific perspective and consulted my best friend who is a doctoral candidate in genetics to make sure I got the science behind my argument correct. My debate piece is broken up into two parts. In this first part, I explain why science has not determined when “life begins here”. Later this week I will post part two, which explains why so called ‘personhood’ amendments are extremely dangerous and threaten to change the very world we live in today. With that little teaser in mind, here is part one.
When does life begin? It is an age old question that science has yet to answer. Scientists understand the processes behind human reproduction. They can tell you step by step exactly what happens from the moment an egg is fertilized all the way through birth, but science has yet to claim that “life begins here.” The reasoning behind this is simple. Determining what makes a set of cells a living organism is a complex process and a living organism must display certain characteristics at the moment of observation to be declared alive. Many pro-life activists believe that life begins at conception, which they define at the moment of fertilization. Those activists pair that belief with the desire to pass ‘personhood’ amendments, which would bestow human rights towards all fertilized eggs. Not only would this rush to define life fly in the face of science, it would be very dangerous and have widespread consequences that are often ignored.
All living organisms must display certain characteristics in order to be considered living. They must have the ability to grow; maintain their internal environment at a constant state (called homeostasis); respond to outside stimuli; display a distinct cellular organization; metabolize chemical energy; have the ability to reproduce as a species; and the have the ability to adapt to their environment.
To put it bluntly, a zygote is not a living organism. A zygote does not exhibit the key characteristics which all living organisms must have in order to be considered alive. Here are two examples to show what I mean. A living organism must respond to outside stimuli. A zygote cannot and does not respond to outside stimuli. Once formed through fertilization of the oocyte, the zygote starts the process of cell division and begins to develop into a morula and eventually a blastocyst. During this process it travels through the fallopian tubes towards the uterus. The zygote does not move on its own accord and instead is guided through the fallopian tubes via tubal cilia lining the tube. Any outside stimuli on the zygote has no effect on the zygote itself. It cannot respond to outside stimulus because it is nothing more than a clump of cells without any organizational structure or set of systems able to respond to outside stimulus.
A living organism must display organizational complexity at the cellular level. A zygote does not display organizational complexity until it develops into a blastocyst and implants into the uterus. Once implantation has occurred, the embryo begins to rapidly grow and starts the process of differentiation, where different organs and body structures begin to form. The key here is that it is not until implantation occurs that we start to see organization complexity.
This is why scientifically you cannot claim a zygote is a living organism. Is it alive? Sure, so are the cells in my heart, but a living organism? Not so much.