[Bob Diamond]: For example, I use forty-eight percent of my brain. Do you know how much you use?
[Daniel Miller]: Forty… seven?
[Bob Diamond]: Three.
-Defending Your Life (1991)
The human brain, with its 86 billion neurons and over 100 trillion connections, remains one of the most enigmatic structures in the natural world. Centuries of exploration and scientific inquiry have brought us to the edge of understanding, yet the complexity of the brain has proven to be a formidable challenge.
In our quest to decipher the workings of this intricate organ, scientists are now turning to the past, unraveling the mysteries of brain evolution through a fascinating journey that spans millions of years.
A Brief History of Intelligence
The first brains had two primary motor programs—one for moving forward, and one for turning.
- Complexity of the Brain:
- The human brain is immensely complex, with over 86 billion neurons and 100 trillion connections.
- Understanding the brain remains a challenge due to intricate connections, chemical signals, and the non-coherent design of evolution.
- Alternative Approach:
- Some scientists propose an alternative approach: studying fossils, genes, and brains of various animals to understand brain evolution.
- Focus on rolling back the evolutionary clock to the simpler first brain and tracking modifications forward in time.
- Five Breakthroughs in Brain Evolution:
- The brain evolved in five key steps or breakthroughs.
- Each breakthrough built on the previous ones, repurposing biological building blocks for new challenges.
- First Brain’s Purpose: Steering:
- The first brain, evolved around 600 million years ago, was designed for steering.
- Early worm-like creatures with the first brains used a simple algorithm based on smell gradients to navigate towards food and away from danger.
- Missing Element in AI: Mammalian “World Model”:
- AI lacks the breakthroughs that emerged in early mammals, particularly the neocortex.
- The neocortex enabled simulation, allowing animals to imagine the future and plan actions ahead of time.
- AI Safety and Primate Brain:
- AI safety involves understanding and inferring human intent, known as the “paperclip problem.”
- The breakthrough of “mentalizing,” found in early primates, enables thinking about one’s own thoughts and predicting the thoughts and actions of others.
- To create safe AI systems, understanding the human mind is crucial to prevent unintended consequences.
The Complexity Conundrum
Before delving into the five breakthroughs, it’s crucial to appreciate the staggering complexity of the human brain. Within a cubic millimeter, a space comparable to the width of a penny, over a billion connections thrive. Neurons communicate through hundreds of different chemical signals, introducing layers of intricacy. The evolutionary process itself adds to the puzzle, with duplicated, redundant, and overlapping circuits obscuring our understanding of how different brain systems interconnect.
The Five Breakthroughs Unveiled
Researcher Max S. Bennett offers a unique view into the ordered steps by which human brains evolved and suggests several unique hypotheses on the mechanisms of human brain function.
First Breakthrough – Steering in Early Bilaterians
The idea is that early animals with bilateral symmetry (like left and right sides) had a big breakthrough in how they navigated their surroundings. This breakthrough involved a steering mechanism that helped them make decisions, such as approaching good things or escaping from bad things.
The animals developed a simple way of categorizing stimuli as either positive (approach) or negative (escape). This allowed them to navigate effectively by turning towards positive things and away from negative things.
The breakthrough was made possible by four important changes in these early animals: a bilateral body plan, specific neurons for sensing positive and negative stimuli, mechanisms for learning from experience, and the use of certain chemicals (like dopamine) to signal positive or negative situations. These changes helped these animals explore their environment, find food, and stay balanced – and it all happened thanks to the evolution of neurons and muscles in their brains.
Second Breakthrough – Reinforcing in Early Vertebrates
The idea is that early vertebrate animals went through some important changes in their brains that allowed them to learn in a new and powerful way called “model-free reinforcement learning.” This type of learning, different from another method called “model-based” learning, helped them with tasks like finding their way around, understanding time intervals, and learning from what was missing. In simple terms, instead of planning out actions, these animals learned by directly connecting what they did with the outcome they got.
The hypothesis suggests that these early vertebrates developed a kind of mental map to remember locations and patterns, and their brains had new structures like the pallium, basal ganglia, tectum, and cerebellum to make this possible. These structures worked together, allowing the animals to connect the feeling of reward or punishment to their actions, helping them learn and navigate their environment better. This breakthrough in learning was likely only possible because of some earlier developments in the brains of simpler animals.
Third Breakthrough – Simulating in Early Mammals
In early mammals, the development of specific brain regions, like the frontal cortex and sensory cortex, allowed for a unique ability to imagine and simulate actions before taking them. This process, called model-based reinforcement learning, was facilitated by the neocortex, which is like a self-training system predicting sensory input. The frontal cortex, especially the anterior cingulate cortex (ACC), was proposed to play a key role in building a kind of mental model of intentions, helping animals simulate different paths and learn from those simulations. The ability to simulate actions internally was seen as a crucial aspect of decision-making, particularly when faced with uncertainty. Later in mammalian evolution, the motor cortex emerged, enhancing the planning of precise movements.
The whole process relies on inherited features from earlier vertebrates, such as spatial mapping and the basal ganglia’s ability to learn from experiences, contributing to the development of the neocortex’s unique capabilities.
Fourth Breakthrough – Mentalizing in Early Primates
The idea suggests that early primates developed special parts of their brain, the granular prefrontal cortex (gPFC) and polysensory cortex (PSC), which allowed them to do something unique called “mentalizing.” This means they could create a model of the mind, understanding intentions and knowledge. This ability was used in various ways, like predicting future needs, understanding others’ thoughts, and learning by watching. The gPFC-PSC network, receiving information from the ACC and other areas, acts like a tool that simulates mind states. This helped primates plan for the future, like going to the store before feeling hungry. This brain feature also enabled them to understand what others might be thinking or learn skills by observing others. Importantly, this mentalizing ability built on the earlier capacity to simulate the world, showcasing a progression in brain function among early primates.
Fifth Breakthrough – Speaking in Early Humans
The idea put forth here is that the special parts of our brains that appeared in early humans were crucial for the development of language and music. The author talks about changes in a brain connection called the “AF-BG network,” which seems to be unique to humans and important for communication with meaning and rhythm. The proposal suggests that language and music both emerged because of this specific brain connectivity.
The author acknowledges that some people have criticized traditional ideas about language development. Still, they argue that language and music are closely connected because they both involve things like keeping a beat in a conversation or a song, having a structure with different levels, and being able to predict what comes next. The hypothesis also suggests that our ability to understand what others know, called “mentalizing,” was a crucial step before we could have effective rhythmic communication. The brain network involved in this, the AF-BG network, overlaps with the areas related to mentalizing.
In traversing the evolutionary tapestry, we witness a symphony of cognitive milestones that have shaped the diverse inhabitants of Earth. From the rudimentary navigation of early bilaterians to the intricate mentalizing of early primates and the eloquent speech of early humans, the trajectory of evolution reveals a continuous refinement of cognitive abilities.
Each breakthrough, building upon its predecessor, is a testament to the adaptive brilliance honed over eons. As we marvel at the complexity of these cognitive innovations, we gain profound insights into the interconnectedness of life’s journey—a journey marked by the relentless pursuit of survival, knowledge, and meaningful communication. The five breakthroughs unveiled stand as beacons illuminating the extraordinary story of life’s intellectual evolution.