Stem Cells: How To Build and Maintain Bodies, Including Plants

Until recently, I didn’t know much about stem cells except that they produced other kinds of cells and that the medical research on them was controversial. In the context of the history of life, it turns out, their importance is as fundamental as you can get.

It took more than a billion years for the first cell with a nucleus to come together. Since then, the only reliable source for a new cell has been another cell. Every cell is an offspring. True for plants as well as animals.

An embryonic stem cell (Wikipedia)

An embryonic stem cell

But while cells are specialized for one task or another, they are not always very good at dividing and reproducing. Muscle cells, blood cells, and nerve cells don’t reproduce at all. Other cells in the body divide only under some circumstances or only a limited number of times.

But reproduction is the stem cell’s specialty. When it divides, it produce another stem cell, ready for the next round, along with a muscle cell or blood cell or nerve cell or a cell of another organ. It looks the part for such flexibility—blob-like, unstructured, not committed until needed.

Stem cells are stationed throughout the body, small groups of them in each organ, like local hospitals on call to repair the sick and damaged. They are a profound piece of bodily engineering, a design for the long-term, like a futuristic car that carries little 3-D printers throughout the engine and chassis to create new parts and replace the old parts automatically.

In human embryos, in contrast to adults, stem cells literally build the body. When an embryo is only a few days old, its stem cells begin to form all—all—of the specialized cells needed in a body, some 200 of them.

In this root tip, the number 1 marks the relatively unstructured stem cells in the meristem. (Wikipedia)

In this root tip, the number 1 marks the relatively unstructured stem cells in the meristem.

Plants have stem cells too. Located near the tips of the roots and stems in a layer called the meristem, plant stem cells divide into both specialized cells for the plant and additional stem cells. Stem cells are, in other words, the place where a plant grows.

One of the wonders of any living thing is the sheer variety of its parts, the inventory of its tubes, organs, fluids, surfaces, protrusions, electric circuits and rigid pieces. As we pause to appreciate this profusion, sing the praises of the smudgy cell that creates and repairs them all.

How Consciousness Might Have Evolved

Human consciousness. Our wonderful, crazy mind. Our personhood. And our quandary. Where did consciousness come from? How did it become part of us?

Michael Graziano, a neuropsychologist I’ve posted about before, writes in the June 2016 Atlantic about how consciousness might have evolved. He starts with the question that evolutionists ask about any feature of an organism: What is its adaptive value?

The answer, he writes, is that consciousness is a sophisticated solution to a difficulty that plagues the nervous system of all creatures: “Too much information constantly flows in to be fully processed.” It’s an old dilemma, with early fixes. Even before the formation of brains, nervous systems 600 million years ago enhanced certain nerve signals at the expense of others. The eyes of insects and crabs, for example, generate “an outline sketch of the world” as the signals carrying visual data about the edges of objects are stronger than other visual signals.

Then around 500 million years ago, a controller in the early brains of fish and reptiles began coordinating several senses at a time, “aiming the satellite dishes of the eyes, ears, and nose towards anything important.” The controller did so by generating an internal model, a set of information about the current state of the body parts, and predicting “how these body parts will move next and about the consequences of their movement.” If you had only a reptilian controller for a brain, you would look at the steps in front of you and the controller would check those nerve signals against its model of where your legs ought to be to get you up the steps successfully.

But we have much more than a controller. Some mammals, including us, have the latest upgrade, the cerebral cortex. We can pay attention to something we are not even focused on at the moment—the TV in the other room, for instance—because our cortex can select what to select. What’s more, we can even be self-aware that we are doing so. “I’m not going to go in there, but he’s watching that news again” (my example). Humans can do this because our upgraded controller uses schemas, models of not only all that we know but also of our attention itself. Our brain tracks “what covert attention is doing moment by moment and what its consequences are.” This is where we get that self-aware voice inside us that tells us, “I’ve got something intangible inside me. It moves around from one thing to another and allows me to understand and remember.”

Such evolution of consciousness goes hand in hand with our social evolution, according to Graziano. Animals acquired the capacity to be aware of the mind of other members of their species. Social awareness and self-awareness have evolved “in tandem….We understand other people by projecting ourselves onto them. But we also understand ourselves by considering the way other people might see us.” Consciousness tracks and grows from our social life and our social self.

Graziano acknowledges that the schema theory of consciousness is still new, but he believes it “provides a general framework” for understanding consciousness and its evolution. It seems to me that it does so very well. It’s difficult for us to see our minds in physical terms because we have that voice in our head that insists, “Wow! I’m thinking and feeling all this!” Glowing with this cerebral radiance, we easily believe we carry an ethereal self, even an undying soul. But it is thrilling to me to understand the splendor of consciousness not as an outlier in nature but as a thoroughly earthly step in the push of small, accidental, pragmatic adjustments that is physical life.


My Four Modes of Everyday Consciousness

I’ve been trying to get a clearer view of the different ways in which my consciousness functions during a typical day. It’s like trying to catch a view of myself in the mirror in a mirror. I’m omitting here the labyrinth of my sub-conscious and looking just at the everyday workings in my head that my head is aware of. I’m including meditation and mindfulness, since I do them every day at a basic level and in different contexts.

The literature divides up consciousness in a daunting variety of ways. But I see in myself mainly four modes.

The first is Awareness. This unfocused, baseline consciousness consists of plain sensory input with little or no processing beyond basic comprehension. It is the opposite of being asleep or unconscious. “Doctor, he’s regained consciousness.” It is the state I’m in when I idly watch a car go down the street, when I watch a movie, when I pick up the remote to change the channel. It includes familiar, unthinking actions like lifting a fork or saying “Hi. How are you?” Awareness feels passive but also primed for responsiveness.

Stream of Consciousness, Gary Buhler (

Stream of Consciousness, by Gary Buhler

My second mode of consciousness is Stream of Consciousness. This is a noticeable flow of words, images, and memories that moves along on its own through my head regardless of my surroundings. Sometimes, for me, this flow gets noisy and intrusive, a kaleidoscope with little or no focus. It includes vivid flashbacks and anxious glimpses of the future. But mostly it consists of words, a sort of thinking-lite. Human consciousness must have changed a lot around 100,000 years ago as the brain began to store names for images of things and for countless abstractions and relationships. The result was that we could say or think, “Why are you doing it that way?” and such flotsam has been popping up in our mental streams ever since.

Next, after Awareness and Stream of Consciousness, there’s Mindfulness. Mindfulness is a concentrated but relaxed and wordless attention to something. I experience brief periods of it during meditation, in between the moments when my Stream of Consciousness washes everything else out of my head for a while. Mindfulness is at the core of not only meditation but also any exercise of concentration such as painting, music, dance and other types of physical exertion. We are mindful when we observe the behavior of a squirrel or, fleetingly, when we take a picture of someone. Sometimes I sit for a minute to grasp the sensation of the night or the ocean or being alive. Such mindful consciousness has the quality of stepping closer to something, allowing us to experience it with greater clarity and peace.

Finally, there’s Language—as used for thinking, talking, listening, reading, writing. Language arose as a social tool, and it is essentially social even when we’re just thinking to ourselves; an audience is implied even when it’s not present. It may pop up in the Stream of Consciousness, but it’s the mental mode for extended episodes of talking, listening, and thinking, problem-solving mood. My wife and I discuss plans for the day, I think about a question for a blog post, I try to make a point in a conversation with someone, and I read a book for pleasure. While mute Mindfulness feels like I’m taking a step closer, language use sometimes feels like I’m stepping around and away from something to see it from other perspectives.

So these are the principle states that I most often catch my conscious mind in the midst of: general Awareness, swirling Stream of Consciousness, concentrated Mindfulness, and purposeful Language use. Trying to classify the different modes of your own consciousness is difficult. Despite your familiarity with your own mind, you may realize it’s not easy to find the categories that capture the differences in what goes on in your head in sensible ways. This isn’t surprising given the brain’s complexity. But the process is enlightening nonetheless. You come out of it seeing yourself differently.