One of the amazing complexities of life is an organism’s ability to recognize and react to its surroundings. This trait of awarness exists in the smallest single-celled organism as well as in the most complex of creatures - that is, Homo sapiens, like you and me.
Bullfrog hiding in duckweed © Joe McDonald/CORBIS


A living organism has thousands of different kinds of protein shapes, enabling it to self-organize and self-maintain, to reproduce and adapt. How is this even possible inside of a single cell? One useful way to think about this is with a concept called “emergence.” There’s a T-shirt slogan for emergence that goes, “You get something else from nothing but.” What does that mean? Well, the nothing buts are important parts of a system that form relationships with, and organize themselves with respect to, one another. When that happens, the something else that wasn’t there before, a new property or capability, pops through.
Let’s think of some examples. We might consider an emergent property like blood circulation. The nothing buts are things like the heart, the arteries, and the capillaries that, working collectively, allow for blood circulation to take place.
There’s a useful term in biology for emergent properties: traits. So blood circulation is a trait. Human-style motility is a trait, and there are countless others. An organism is thus a collection of traits. When we speak of traits, we are thinking of the large emergent part rather than the nothing buts, but we can go all the way down to the molecules, breaking the trait into little pieces, or numerous nothing buts. Then, when we put Humpty Dumpty back together again, when we assemble all the pieces and get the emergent property, we start talking about the traits that are generated.
Critical to all of this is the idea of natural selection — the process that brings new kinds of organizations and traits from one generation to the next. Natural selection is looking at traits such as blood circulation and motility. It’s not looking at the proteins and protein shapes. It can’t see the genes. It has no idea how the traits are generated. The criterion for selection is whether a particular version of a trait is adaptive (favorable) or not adaptive (unfavorable) to the particular environmental context where the organism is making its living.
Traits materialize and then evolve. An example of one trait that’s evolving — and that we’re particularly interested in — is what we call “awareness.” So how does awareness work?


Probably the very first organisms that were ever successful already had some ability to be aware of their environment: to figure out where a food source is, or where light is. And the basic organization of awareness is shared throughout the biological world.
First, some sort of an outside signal exists for an organism to be aware of. Then, the organism must have a receptor looking for that signal. The receptor is usually a protein, and when the signal and the receptor interact, the protein changes its shape. In your nose, for example, the odor receptors are one shape when you’re not smelling anything; but when a particular odorant comes in, certain receptors bind to that odorant and change their shape.
Close-up of the amoeba Chaos (Pelomyxa) carolinensis surrounding paramecium prey with its pseudopods © Carolina Biological/Visuals Unlimited/CORBIS
What happens next is a whole cascade of what we call “downstream events.” The cell notices the shape change, and more shape changes are stimulated. Finally, there’s an adaptive response. If an organism has smelled something, it gets the response to either go toward the thing (if it decides that it is good and wants to eat it), or to move away from it (if it’s the smell of, say, a predator or some toxic substance). Such changes and responses occur even in bacteria, which happen to be very aware of their environment.

Neurons and brains

You can see the evolution of awareness throughout the single-celled world, but animals took the whole awareness idea to another level by inventing particular kinds of cells called “neurons.” Many neurons tell muscles whether to contract or not. They’re called motor neurons. Another group of important neurons, called sensory neurons, have sensory receptors.
Neurons ©
In animals, sensory neurons are almost always hooked up to the brain. The brain is a collection of additional neurons that interacts with the input pouring in from the sensory neurons and integrates the signals. A brain makes things multichanneled and allows for multitasking. You can see a signal. You can smell a signal. You can touch a signal. You can taste a signal. All of these inputs come into the brain, and the neurons in the brain hook all of that information together and figure out the most appropriate response. Are you in the presence of predator or prey?

Learning and memory

Another wondrous trait is the brain’s ability to learn and remember. The thinking used to be that only more highly developed animals could store information in memory, but recent research has shown that even something rather simple, like a clam, with only about 20,000 neurons in its brain, can remember for several days stimuli it received.
Animals like mammals can have millions or even billions of neurons in their brains, and any one neuron in the brain is in contact with, and can be stimulated by, a thousand other neurons. Complicating things further, some of the neurons that relate to a given neuron stimulate it and cause it to fire, while others prevent it from firing. So whether the neuron actually fires is a result of their collective input.
Imagine that multiplied by about 100 billion, and you’ll begin to see why it’s hard to puzzle out how a complex mammalian brain might work. In fact, there’s very little that we do understand about it. We know that because brains can remember, a mammal with a huge memory store is not only aware of what it’s sensing in the moment, it’s also aware of all the things that it remembers. So it’s much more knowledgeable about the world than if it just had a protein receptor reacting to an outside signal, as with a single-celled organism.
Tower of Babel by Pieter Bruegel the Elder © The Gallery Collection/CORBIS

Language and the self

What about human brains? How are they different? Well, they don’t look very different than other mammalian brains, and they control most of the same activities, like breathing and body temperature. But they do other things as well. The most important and interesting new feature is our unique mode of communication, called “symbolic language.” We have a way of thinking that generates abstract ideas, and we can remember these abstract ideas and put them together in spoken and written language. We also use language to teach one another, rather than learning only from experience and imitation, and to transmit and evolve our ideas from generation to generation via the social system we call “culture.”
Another crucial feature is our storytelling ability — we are narrative creatures, and each of us has a self-narrative. Our “I-self” wakes up in the morning, goes to bed at night, and remembers things about its life. This I-self is crucial to our experience, and it probably distinguishes us from all of the other animals on the planet.
By Ursula Goodenough