The concept of the “self” has long been considered philosophically significant: a foundation for exploring who we are and why we’re here. But where does the self begin?

Developmental biologist Michael Levin explores this question, explaining how the “self” is constantly being constructed and created, starting in the early moments of embryogenesis. 

Levin argues against binary categorizations of selfhood, emphasizing that it is a continuous phenomenon with no sharp lines between different stages of development. Using the example of self-organizing cells in the formation of the embryo, Levin also asserts that the self is not a singular entity — rather, it is a collection of structures working together toward a specific goal.

Michael Levin: The concept of a self: I actually think it's really critical, and it goes all the way back to the beginning of life and the beginning of development for all of us. And I think it's really important to understand that the contents of your mind, your self model, your model of the outside world, where the boundary between you and the outside world is—so where do you end and the outside world begins—all of these things are constantly being constructed and created.

The deep notions that we are not a static entity, but rather a constantly self-constructing entity, start all the way back from the earliest moments of embryogenesis. If you take a flat blastodisc, in that case of a duck and this was discovered by Lutz in the 1940s, is take a little needle and you make scratches in that blastoderm, and so when you do this, you basically separate that initial blastoderm into islands. And what happens is that for the next few hours, every island is not going to be able to sense the presence of the others and it's going to self-organize into an embryo and eventually they'll heal up and then you'll get a single blastoderm.

But by then what you've got is a collection of conjoined twins. And it might be two and it might be three and it might be a half a dozen. And so the question of how many selves are in a particular embryo is actually unclear at the beginning. You don't know that because what it is is this kind of an ocean of potentiality. And so this just shows you that a biological self, this has to construct itself out of some medium and figure out where the borders are and where are the boundaries. We are a dynamic process right from the beginning.

One technique that I like to use in helping to think about these various categories is walk backwards in your development until you're basically an embryo. And then eventually you come to the point where you were an unfertilized oocyte. But there are tens of thousands of cells. What are we counting when we say there's one embryo there? There really isn't one of anything. There are many, many, many individual cells there. What we're counting is alignment, the fact that all of those cells are committed to working together towards building a specific structure.

You could also do the same thought experiment on an evolutionary timescale and you start with a modern human that you might think has certain capacities, moral responsibilities, and various other metacognitive skills — and just walk backwards and ask which of our hominid ancestors did and did not have them? And it's pretty clear that it's not going to be possible to say, "This set of parents didn't have it, and then they had an offspring and boom, that offspring now has it." And so, it's a very long continuous process developmental biology offers no specific place where you can draw a sharp line and say, "Okay, at time T, this was just physics and chemistry. But look, they're the cognition now appeared." And so, these binary categories are completely dissolved if you actually take the biology seriously and follow it all the way, all the way down to the beginning. If you were try to define it, I think "the self" is the answer to the question, "What is the system that can be counted on to do various things?" As you look into the outside world, all of the objects you see and that you deal with are answers to the questions of: "What can I expect to happen next?" So I think the question of the self is critical. It's critical to understanding what the world is to have a model of yourself and that model, if you've ever watched a baby, whether human or otherwise for the first time trying to figure out what does it have control over. Telling that story about what you are is really critical for functioning in the world. And a lot of people get very depressed over the certain scientific stories, 'That we are nothing but'- so we are nothing but chemistry and physics; we are nothing but genes. And so we hear a lot of these stories that 'We are nothing but' and so the question of what we are is important and fascinating, but it's not nearly as important as, "What do we do next?" And I think all of biology is, and I think we should be as well, much more focused on what is the best thing you can do next regardless of what the current scientific story is of what you are or what you might be.