Bilateral body structure
The earliest animal relatives, such as corals, anemones, and jellyfish, had radially symmetrical body structures. However, most animal species today exhibit bilateral symmetry. Bilateral symmetry allows the animal's locomotion system to be optimized for a single direction (forward), while solving navigation problems by adding steering mechanisms.
Animals with bilateral symmetry are the only creatures that possess brains. The earliest brains evolved alongside bilateral body structures for the same purpose: to help animals navigate effectively through steering. For multicellular organisms, the ability to steer was an important breakthrough.
The earliest brains were as simple as those of nematodes. For example, the brain of Caenorhabditis elegans consists of only 302 neurons (in contrast, the human brain has approximately 85 billion neurons). Despite its simplicity, the nematode exhibits relatively complex behaviors. Nematodes not only move toward targets (such as food) but also avoid adverse conditions (such as light, harmful cold or heat, or sharp surfaces).
The first robot
The world's first robot was created by Rodney Brooks, a robotics expert at MIT. He proposed the principle of "building intelligent systems step by step, with each step having a complete system." This is similar to the process of biological evolution, starting with a simple brain and gradually increasing complexity. Brooks' first step echoed the first step in brain evolution—starting with steering. The Roomba vacuum cleaner has an extremely simple sensor and brain, while presenting a bilaterally symmetrical structure, enabling it to navigate in a complex world, even though it does not truly understand or simulate this world.
In markets, as in evolution, the three most important things are always rewarded first:
Products that are inexpensive Products that are useful Products that are simple enough to be discovered first
Although steering itself may not be as impressive as other intellectual achievements, it is indeed inexpensive, highly practical, and sufficiently simple in evolutionary fine-tuning. Therefore, the evolution of the brain began precisely from this point.
The value of stimuli
The breakthrough in steering function of bilaterally symmetrical animals required them to divide the world into two categories: objects to approach ("good things") and objects to avoid ("bad things"). This simple binary classification is the way the most primitive brains perceive the world.
This binary classification is very similar to the simple judgment method humans use during early development. As I discussed with a psychologist, in our growth from childhood to adulthood, we often evaluate the world in a simple "good" or "bad" manner. This binary thinking is very common in the early stages of our growth because it helps us quickly and intuitively understand our surroundings.
However, as we grow older and gain more experience, we gradually learn to introduce the concept of "gray areas," meaning the world is not always black and white but full of complexities and nuances. This cognitive development, like brain evolution, is a process from simplicity to complexity. The gradual learning to accept gray areas can also be seen as one of the important signs of our psychological maturity.
. Value refers to the degree of goodness or badness of a stimulus, unrelated to moral judgment. It is a more fundamental biological mechanism that determines whether an animal will respond to a stimulus by approaching or avoiding it.
; chemicals, images, or temperatures themselves have no inherent goodness or badness. Instead, the value of stimuli is subjective, entirely determined by the brain's evaluation of the stimuli.
For temperature, nematodes have two key regulatory circuits:
a "too hot" negative neuron that triggers steering when the temperature exceeds a certain threshold, prompting the nematode to avoid high temperatures; a "too cold" negative neuron that triggers steering when the temperature falls below a certain threshold, causing it to avoid cold environments.
These two negative neurons interact, allowing the nematode to quickly move away from heat sources when the temperature is too high or avoid cold environments when the temperature is too low.
—which contains temperature-sensitive neurons that work similarly to nematode neurons, regulating body temperature to ensure survival.
Trade-Offs
When animals face multiple stimuli, how do they choose the direction to steer? The answer is:
Specifically, it depends on the relative concentrations of "good things" (such as food odors) and "bad things" (such as copper odors). The forward-moving neurons and steering neurons in the animal's body inhibit each other, allowing the entire neural network to integrate these trade-offs and make decisions—whichever neuron accumulates more "votes" will prevail, determining whether the animal will cross the copper obstacle and continue moving forward.
Even the simplest brains, such as those with fewer than a thousand neurons, can perform this complex weighing mechanism. This ability stems from the evolution of inhibitory neurons in radially symmetrical animals (such as early coral-like animals). Inhibitory neurons mentioned in the previous discussion on pre-brain neurons are the same inhibitory mechanisms now used in bilaterally symmetrical animals to assist in making trade-offs in complex steering decisions.
In addition to relative concentration, it also depends on the nematode's level of hunger. Neurons are more sensitive to food odors when hunger signals are present and less sensitive when satiety signals are present. The aforementioned Roomba vacuum cleaner also uses the same mechanism—when fully charged, it ignores signals from its base; when the battery is low, signals from the base become positively valued (modulate valence).
Emotions
two important dimensions.
In the first-generation brains of simple organisms like nematodes, we can also observe the rudiments of these states.
—after external stimuli trigger behavior, the behavioral pattern persists for some time even after the stimuli fade.
A similar design can also be seen in the first-generation robot, Roomba. When Roomba detects dirt, it activates dirt detection mode and repeatedly cleans around the dirt area. Even if the dirt is no longer detected, Roomba continues to turn around in this area for a while to ensure thorough cleaning.
, such as dopamine and serotonin. These chemicals regulate neuronal activity; if excitatory and inhibitory neurons are analogous to "0" and "1" in computers, then modulatory neurons control neural activity through complex chemical signaling.
For example:
: When nematodes detect food in the environment, dopamine secretion increases, telling them "something good is happening nearby," driving the pursuit of food ( : When nematodes have food inside their bodies, serotonin secretion increases, telling them "something good is happening," driving the enjoyment of food (
(such as opioids) initiate the recovery process, gradually returning the organism to normal.
state, where arousal and motivation gradually shut down. At this point, serotonin secretion increases, but dopamine response becomes dull, leading to anhedonia, which resembles depression symptoms in modern humans. Psychology also has a specific term for this state: learned helplessness.
Emotions first appeared 550 million years ago in bilaterally symmetrical animals, primarily guiding them to make key steering decisions:
Regarding learned helplessness, there is an experiment conducted late in Pavlov's career. His most famous work is the "Pavlov's dog" experiment, which pioneered classical conditioning research. However, during Stalin's era, Pavlov also conducted a controversial experiment later in his life, which is generally avoided in academic circles due to its cruelty and ethical violations. In the experiment, Pavlov placed animals in near-death environments to observe whether any could "persevere" and survive. Ultimately, he found that all animals eventually collapsed after being repeatedly subjected to near-death situations. Moreover, the longer an animal persisted before collapsing, the greater the collapse and the longer the recovery time. This demonstrates that, in the face of disasters, no one can truly escape unscathed, and all eventually fall into the trap of learned helplessness.
Summary
Steering requires at least the following elements:
A bilateral body plan for steering Valence neurons for detecting and classifying stimuli into good and bad categories A brain for integrating inputs into a single steering decision The ability to modulate valence based on internal states Feelings further enhance the effectiveness of steering