The Evolution of Human Thought

Martin F. Nimbach, November 2024

The Evolution of Human Thought

Following a long sequence of evolutionary coincidences, punctuated by periods of stasis, the brains of our ancestors eventually reached a level of capability around 100,000 years ago that we now recognise as distinctly human. This advanced cognitive equipment enabled early humans to make intelligent decisions, formulate plans, and apply their experiences intuitively, in addition to their instinctive "knowledge."

Humans already possessed an exceptionally strong procedural memory, which allowed them to learn and perform complex sequences and actions with routine ease. This memory, often referred to as "experiential knowledge," enabled early humans to engage in skills such as hunting, gathering, and tool-making almost automatically, without consciously recalling each detail. This foundational ability underpins many everyday activities that we still master effortlessly today, illustrating how evolution prepared the human brain to handle practical challenges. With this essential toolkit for daily life, new possibilities began to unfold.

Initially, however, they remained primarily reactive beings: like other animals, they could respond intelligently to their environment, yet without consciously questioning their actions or weighing alternative possibilities.

Humans have been evolutionarily shaped as social beings. From the very beginning, they depended on community for survival, protection against environmental dangers, and the successful rearing of offspring. In a world fraught with uncertainties, close-knit group living was crucial to the welfare and safety of each individual. This community not only provided protection but also served as the foundation for passing on essential knowledge and experiences vital for survival.

The ability to communicate became indispensable in organising and enhancing life within the group. Sharing information, issuing warnings, exchanging strategies, and expressing emotions all strengthened group cohesion and created a "social network" that bonded people closely and ensured community stability.

Early humans began to advance their communication skills in tandem with their emerging cognitive capabilities, gradually learning the art of speech. Simple gestures evolved into the first words, words grew into concepts, and eventually, these combined to form complete sentences.

The Significance of Language

Around 80,000 years ago, human language reached a critical milestone. For the first time, humans could not only communicate with each other but also engage in communication with themselves. Complex articulation allowed them to conduct inner monologues—a process we now refer to as "thinking." These inner dialogues introduced an entirely new approach to decision-making: external stimuli no longer had to be the sole triggers for action. Early humans could now consciously retrieve and process memories, evoke emotions, or actively learn through deliberate repetition.

This linguistic evolution was ground-breaking for the development of human thought. It laid the foundation for building social structures, exchanging knowledge, and developing complex lines of reasoning—the very cornerstones of culture and society as we know them today.

The ability for self-reflection and internal dialogue set humans apart from all other species and led to the emergence of a new dimension of consciousness. For the first time, it became possible to think beyond the immediate present, to analyse the past, and to contemplate future possibilities. This new mode of thought enabled humans to make conscious decisions, formulate plans, and ultimately develop a sense of their own existence and place in the world.

From this way of thinking emerged questions about one’s own being and the contemplation of an existence beyond death. Humans began to create burial sites and include grave goods—a clear indication of an early belief in an afterlife. These burial findings allow us today to trace the origins of human thought and consciousness.

Thinking, Fast and Slow

The Nobel laureate Daniel Kahneman and Amos Tversky developed the concept of “System 1” and “System 2” thinking to explain how humans process information and make decisions. This distinction provides valuable insights into the mechanisms of our thinking and helps to explain why we are often prone to cognitive biases.

“System 1” represents the faster, more automated way of thinking. It operates unconsciously, spontaneously, and with minimal effort, relying on instincts, intuition, and so-called heuristics—mental shortcuts that allow us to make swift decisions, though they may not always be entirely rational. “System 1” decisions are often based on prior experiences and occur intuitively.

Instinct is deeply embedded in our biology; it is innate and typically serves survival purposes. Instinctive reactions, such as withdrawing a hand from heat or the protective drive toward offspring, occur automatically and without conscious thought—they are triggered by specific stimuli and function similarly across all members of a species.

In contrast, intuition is a feeling or insight based on our experiences. It arises as the brain gradually recognises and processes patterns without us being consciously aware of it. When a decision “feels right,” it’s often because our brain has quickly synthesised information and past experiences into a rapid assessment. Intuition, therefore, is individual and evolves with our experiences.

A heuristic is a mental shortcut that the brain uses to make quick decisions or solve problems without thoroughly analysing all the information. Heuristics help us act efficiently by breaking down complex questions into simple rules of thumb. This form of thinking is highly energy-efficient and allows humans to make quick decisions by drawing on simplified thought patterns. Yet, this efficiency makes thinking susceptible to cognitive biases. Until the development of advanced communication and language skills, humans primarily relied on “System 1” thinking: a fast, automatic, and intuitive system that operates without conscious effort.

“System 2” thinking contrasts with the rapid, intuitive “System 1”: it involves conscious, reflective, and analytical processes. This system demands more energy but enables deeper engagement with complex problems. The ability to conduct inner dialogues and pose questions to oneself played a critical role in the development of “System 2” thinking. These self-reflections are the foundation of thoughtful decisions and nuanced analyses—skills that became increasingly important over the course of human evolution.

“System 2” comes into play when a situation demands more focus and careful analysis, such as when confronted with complex or unfamiliar problems. It operates more slowly than “System 1” but is more precise and less prone to errors in thinking, as it scrutinises information carefully and critically challenges the assumptions of “System 1.” Decisions made through “System 2” are based on a conscious consideration of all available information, allowing us to solve complex problems and devise long-term plans.

However, “System 2” is also resource-intensive, requiring substantial cognitive energy and focus, and is often only activated when absolutely necessary. In stressful or hectic situations, it can be more challenging to engage “System 2,” as the energy expenditure is particularly high, often causing us to revert to the quicker “System 1.”

Demanding cognitive effort leads to a higher concentration of glutamate in the brain compared to simpler mental tasks. Glutamate is the primary excitatory neurotransmitter in the central nervous system and plays a central role in signal transmission between nerve cells. It is also crucial to synaptic plasticity—the brain’s ability to change and adapt connections between nerve cells, an essential mechanism for learning and memory formation. Glutamate accumulates especially in the prefrontal cortex, a brain area active when people solve complex problems or make plans. The increased glutamate concentration following intense cognitive work can induce fatigue, which serves as a self-protective mechanism of the brain. This fatigue signals a need for rest to prevent overload and maintain the brain’s long-term functionality.

Kahneman and Tversky demonstrated that “System 1” and “System 2” do not operate in isolation but complement each other. “System 1” often makes quick decisions that help us function efficiently in daily life, while “System 2” intervenes when a situation is more complex or when the decision is particularly significant. However, even this collaboration has its limitations: people often rely too heavily on “System 1,” even when a more thorough, analytical approach is required.

The Impact of Writing and Reading

Knowledge was initially passed down orally in the form of stories and legends shared from generation to generation. This oral tradition served not only for entertainment but also as a crucial means of preserving essential knowledge—about hunting techniques, medicinal plants, dangers, and social norms. Through storytelling, complex lessons and collective experiences were conveyed, accumulating over millennia and forming an early kind of cultural memory. This process led to the development of myths and legends that shaped people's understanding of the world, laying the groundwork for shared values and beliefs.

During this period, humans lived in small, nomadic groups or clans, typically consisting of about 15 to 20 individuals. These groups were constantly on the move in search of food and suitable places to camp. A shared campsite was the centre of their lives, where they found protection, pooled resources, and formed social bonds. The small group size was crucial to their survival, allowing them to respond flexibly to environmental changes and match their needs to the available resources.

British anthropologist Robin Dunbar discovered that the cognitive capacity of the human brain enables us to maintain stable social relationships with around 150 people. This figure, known as the “Dunbar Number,” represents the upper limit of personal connections the brain can manage. It continues to influence the structure and dynamics of social groups in large organisations, social networks, and communities today, marking the maximum number of close connections we can sustain.

However, with the advent of the Neolithic era around 12,000 years ago, humanity faced new challenges. The development of agriculture led to settled living, and large settlements began to emerge. Farming enabled a more stable food supply, spurring population growth and giving rise to larger communities. In Jericho, for example, around 11,000 years ago, an estimated 1,000 to 2,000 people were already living together—a dramatic shift from the small groups and clans that had previously prevailed.

These early large settlements presented the challenge of interacting with far more individuals than Dunbar’s Number. To manage life in such large groups, new social and organisational structures developed. This period saw the rise of early forms of administration, social norms, and cultural rituals that organised and stabilised community life. Beyond personal relationships, humans began to develop collective identities and shared values, laying the foundation for complex societies.

Out of this necessity, the first forms of writing emerged around 5,600 years ago. Initially, writing served mainly administrative purposes, to record and communicate information, particularly in trade, governance, and religious contexts. These early scripts were highly symbolic, often inscribed directly into materials like clay, stone, or metal. In this fixed, durable form, writing helped preserve and transmit complex information over extended periods.

Around 1,000 years later, writing began to be used beyond mere practicality, capturing ideas, thoughts, and emotions. This development laid the foundation for poetry and literature, opening new possibilities for expressing human experience in words. An early example is the Epic of Gilgamesh (circa 2,100 BCE) from Mesopotamia, considered one of the oldest known literary works. This epic poem, preserved in cuneiform on clay tablets, recounts the heroic deeds and adventures of the legendary King Gilgamesh. In this way, early cultures created not only records but also the first literary artworks, providing us with valuable insights into the lives and thoughts of ancient times.

The Cognitive Limitations of Human Memory

Human short-term memory functions as a passive buffer with limited capacity. In 1956, American psychologist George A. Miller proposed the “Magic Number 7,” observing that people can typically hold about seven “chunks” of information (plus or minus two) in short-term memory at a time. However, short-term memory is limited not only in capacity but also in duration: information remains available here only briefly, usually a few seconds to around a minute, unless actively rehearsed or internalised.

The working memory, as an active buffer, takes it a step further. It can not only store information but also actively process and reorganise it. Yet, even working memory has its limits: information can only be retained for seconds to a few minutes unless reinforced through repetition. Each new piece of information can displace older ones, creating a continual process of updating.

The ability to write down thoughts, creating an “external memory,” marked a major milestone in the development of human cognitive abilities. Writing enabled people not only to “buffer” and organise their thoughts but also to make them accessible and permanently available to others. By recording information, humans extended the boundaries of individual memory, laying the foundation for preserving and passing knowledge across generations.

Reading and Writing as “System 3” Thinking

In a way, writing could be described as “System 3” thinking. Unlike the fast, intuitive “System 1” and the slower, analytical “System 2,” writing allows us to externalise and structure knowledge and complex ideas for the long term. It acts as an external system that stabilises our thinking and preserves it in a way that exceeds the fleeting capacities of the human mind. This “System 3” has greatly advanced human culture and science by enabling ideas and facts to be stored, expanded upon, and shared across centuries and vast distances.

Another aspect worth noting concerns the initial materials used for recording text. Early on, only rare and valuable resources like stone, papyrus, or wood were available. This scarcity compelled people to express themselves with precision and focus, as space and resources were limited. To meet these demands, complex writing systems evolved alongside spoken languages. This need for concise expression honed cognitive skills and encouraged the development of analytical and structural thinking processes, shaping how we generate, store, and communicate knowledge to this day.

These advancements laid the groundwork for comprehensive cultural evolution and the intentional transfer of knowledge. This journey reached another major milestone with the invention of the printing press in the 15th century. The printing press revolutionised the dissemination of knowledge, enabling the duplication and rapid distribution of texts on an unprecedented scale. For the first time, knowledge and ideas became accessible to a broader population, forming the foundation for education and the collective knowledge that underpin modern society.

New Media

The internet marked a further, fundamentally transformative step in the evolution of human thinking. It reshaped access to knowledge by connecting people worldwide in real time and making the full range of human understanding available anytime, almost anywhere. While the printing press accelerated the spread of knowledge, the internet created an interactive and collaborative landscape, where ideas can be not only consumed but also immediately shared, refined, and debated. This global network has unprecedentedly expanded the speed, reach, and diversity of knowledge dissemination, allowing humanity to collect, store, and preserve knowledge within a shared digital memory for future access.

Large Language Models (LLMs) are advanced AI models trained on vast amounts of text data to understand and generate language. Using complex neural networks, typically based on the Transformer architecture, they identify patterns in text and process natural language. LLMs like GPT (Generative Pre-trained Transformer) can answer questions, compose text, provide translations, and summarise content by recognising patterns and structures in their training data.

Due to their immense capacity and contextual understanding, LLMs support a range of applications—from content creation to data analysis and scientific research. The next significant leap in human cognitive development may very well arise from the intelligent use of LLMs. These models offer more than a mere “storage drive”; they provide direct, conversational access to the collective knowledge of the world.

Interacting with Artificial Intelligence as “System 4” Thinking

Just as early forms of thinking involved using language and internal monologues to stimulate our cortex to retrieve memories and knowledge, we can now interact with Large Language Models (LLMs) to expand our mental landscape and gain new perspectives. This form of thinking might be termed “System 4”—a new phase that elevates human cognition to a different level through artificial intelligence.

However, this “System 4”–supported by LLMs–also introduces new responsibilities. Just as our intuitive “System 1” is prone to cognitive biases and “System 3” may contain misinformation, the answers provided by this new system should be approached with a critical mind-set.

LLMs can deliver incorrect information as they are trained on vast amounts of text data from the internet and other sources, which often contain inaccuracies, out-dated knowledge, or errors. These models recognise patterns in data, yet they lack true understanding and cannot distinguish fact from fiction. Their responses are based on statistical likelihoods—they generate the most probable answer to an input without verifying its truthfulness.

Additionally, there is the phenomenon of “hallucination”: LLMs can generate convincing but entirely fabricated content. This combination of limited understanding and lack of verification means that, while LLMs can provide useful answers, they may also spread misinformation.

Just as it is important to reflect on and verify our own thinking processes, it is equally vital to approach the information and analyses provided by an LLM with healthy scepticism. The ability to critically assess “System 4” responses reinforces our “System 2” thinking and allows us to use this technology responsibly and thoughtfully to enhance our own learning and thinking.

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