Hello Interactors,
It’s been a while since we’ve been together. I took some time over the holiday break. We often think of parents spoiling kids upon their return from college, but I’m the one who feels spoiled.
We’re squarely in the winter season up north and that means I’ll be exploring human behavior. With all the talk of AI, I thought I’d start with its root inspiration — the neuron. How did these come to be?
Let’s find out.
As I stand here today, the earth’s declination angle is slowly inching toward zero as its orbital tilt brings us closer to spring. This will trigger a host of biological and biochemical chain reactions. Plants awake, buds break, birds migrate, insects propagate, amphibians’ mate, seeds germinate, furs abate, and soils emanate. Algae plumes bloom, and our own metabolism’s resume.
This shared sensing of environmental change makes common sense because we can sense it with our own senses. Less common is making sense of what we can’t sense. That’s what I’m trying to make sense of. Let’s start with cells.
Cells can also make sense of their environment, and of each other. Consensus belief says cellular life emerged nearly 3.7 billion years ago on a rotating and orbiting earth that had already been oscillating in a predictable pattern for 750 million years.
Early cellular organisms learned to predict these patterns, as the theory goes, getting an evolutionary leg up on the competition.1 This knowledge was then stored in the cell. I was surprised to learn a cell can store information.
Ricard Solé is a prominent researcher who applies complex systems concepts to biology. He explained in a recent podcast how cells perform associative learning through reactions to different external stimuli — a process fundamental to the evolution of cognition.2 This learning involves associating a specific signal with a stressor in a cell’s environment. Over time, they learn to respond to the signal, even in the absence of the original stressor. A bit like a Pavlovian response.
This information is then stored within the cell. Cells have complex signaling networks that gather information from the cell membrane and transmit it internally from the membrane to the genome or nucleus. These signals act as boolean "genetic switches." The switch involves pairs of genes that negatively regulate each other, creating a kind of memory storage system. As one gene tries to regulate the other, that gene is trying to do the same. Like two magnets competing to repel or attract. This leads to a binary outcome — the conflict produces a specific protein, or it does not. This process is akin to the binary electronic circuitry found in signaling networks used to process and store information on a computer. (more on that in future posts on this topic)
Cells that can respond to the environment, or conditions within itself, can secrete something into their environment. But if there are no other cells to receive them as signals or with the intention to propagate their stored information, this operation serves no function. Over evolutionary time, however, cells began to form functionalities. For example, through expressions formed from their genetic circuitry, the cells that make up your liver and kidney evolved to conduct basic metabolic functions. Meanwhile, the cells that make up neurons in your brain evolved to send and receive information — to communicate with each other. A major step in evolution.
Another major evolutionary step, according to Solé, came with interneurons. These are neurons that form connections between sensory neurons to process information between them. Many neurons connected by many interneurons form arrays of neural circuits capable of more complex information processing. Organisms that don’t have interneurons, like plants, pose a real biological and evolutionary disadvantage among energy competing biological organisms. Though, they created their own biological functions that are so wondrous they induce jealousy, like photosynthesis. Imagine getting fed by lying in the sun with your feet in the sand. Did I mention it’s winter in the gloomy northwest?
Solé believes the invention of interneurons provided the critical step toward a key component in the evolution of complex organisms like us, but also organisms that came before us like jellyfish. Jellyfish are made of a distributed ‘nerve net’ composed of sensory neurons, motor neurons, and interneurons similar to ours. This network conducts basic processing for various sensory and motor functions. For example, it can sense elements of its environment, like water currents and temperatures, which then trigger responses like swimming or eating.
Directed locomotion in response to sensory information processing serves as another critical step on the path of evolution — predation. Not only is the jellyfish sensing the water around them, but they’re also sensing the presence of predators and their nervous system conspires to act accordingly. As remarkable and complex a jellyfish is at storing information that allows it to predict and act to internal and external stimuli, it took another evolutionary leap to yield the kind of complex neural networks and biological systems we humans rely on.
In the words of Ricard Solé, “we tend to think [we humans], unfortunately for our planet, [] have been very, very successful.” He considers humans ‘ecological engineers’ because we can “transform the planet by changing flows of energy and matter at massive scales.” The question remains (as we transform the planet in ways that make it harder for us and the organisms we rely on to survive) is our evolutionary journey entering a phase transition? Are we teaching our cells a new lesson to be stored away for future generations, or another failed biological experiment nearing the end of the relentless and brutal path of evolutionary trial and error?
Paraphrasing the esteemed biologist E. O. Wilson, Solé offers that “if humans were not here, there would be the planet of the ants”. Ants have a form of collective intelligence that also allow them to transform the planet at massive scales, but to also survive seemingly insurmountable odds.
Is there something to be learned from ants? An ant, on its own, is as unremarkable as it is doomed. Can the same be said for us? Who are we without other humans? And even when we’re alone, are we really? We host an entire ecosystem of microorganisms for which we are mutually dependent for survival. Some feed on us, some try to kill us, while others conspire with our cells in competition and collaboration to make sense of each other — including the cells that make neurons. What kind of intelligence will they we need to survive another trip around the sun?
Edgar, R., Green, E., Zhao, Y. et al. Peroxiredoxins are conserved markers of circadian rhythms. Nature 485, 459–464 (2012). https://doi.org/10.1038/nature11088
Carroll, Sean, host. "Ricard Sole on the Space of Cognitions." Mindscape. Episode 260. Sean Carroll, January 1, 2024. https://www.preposterousuniverse.com/podcast/2024/01/01/260-ricard-sole-on-the-space-of-cognitions/
Neurons, Jellyfish, and Ants: Tales of Evolutionary Intelligence