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Endnotes – Looking Back in Time
Think of this as a companion to Looking Back in Time — a place to collect the data points behind the story.
This post reflects on the evolution of human intelligence. While other animals such as octopi and birds show impressive problem-solving, only humans scaled intelligence into a planetary force. To apply the principles of observation, consequence, and action, I start with ten fixed points in Earth history.
Milestones in the History of Life
- Formation of Earth: ~4.54 billion years ago
- First detectable life: ~3.5–3.8 billion years ago
- First vertebrates: ~520 million years ago
- First primates: ~55 million years ago
- First Homo species: ~2.4 million years ago
Major Mass Extinctions
- End-Ordovician: ~444 million years ago
- Late Devonian: ~372–359 million years ago
- End-Permian: ~252 million years ago
- End-Triassic: ~201 million years ago
- End-Cretaceous: ~66 million years ago
Extinctions earlier than the Ordovician almost certainly occurred, but are less well documented. Each extinction acted like a reset — clearing space for new evolutionary paths.
Observations: On Earth History Data
First signs of life
At least 700 million years passed between Earth’s formation and the first detectable life. Whether life arose here or arrived from elsewhere, this is the baseline from which advanced forms developed.
Development of the spine
The evolution of the spine and primitive brain, around 520 million years ago, was a breakthrough — a platform architecture. It took ~3.3 billion years (≈86% of the time since life began) to get here. Once established, the spine endured five mass extinctions.
Development of the human brain
Primates appeared ~55 million years ago, with intelligence similar to today’s monkeys or lemurs. It took ~465 million years after the first vertebrates to reach this stage. Early Homo species then emerged only ~2 million years ago — in the last ~0.05% of Earth’s biological history since the first life appeared.
Consequences Drawn from Earth History Data
First signs of life
This is unlikely to be the absolute start of life in the universe, but it is the baseline for advanced forms here.
Development of the spine
Because ~86% of evolutionary time was required to establish the vertebrate platform, the spine and primitive brain must be highly complex and robust. Evolution advanced through random variation tested by survival — many failures, a few rare successes, then iteration from there.
Development of the human brain
By ~55 Ma the platform for human intelligence was set. Moving from primates to Homo in just ~0.05% of the time since life began highlights how adaptable neurons are. Once the architecture was in place, intelligence did not require a new kind of cell — only more of the same, wired in increasingly flexible patterns. This modular construction explains why the leap to humans was so compressed in geological time: evolution finally had a platform robust enough to run a much bigger program, and intelligence was the output.
Computer system analogy
- Hardware (spine and neurons): fixed, slowest to evolve, hardest to change.
- Firmware (instincts, limbic system): survival programs, adjustable only across generations.
- Software (frontal cortex): flexible, reprogrammable in a lifetime.
Humans didn’t get a different kind of brain cell than a primate — we simply run more of them in the frontal cortex, with more flexible “software.”
Extinction as a catalyst
Extinctions eliminated dominant lineages and cleared paths for others. The dinosaurs’ removal at the end-Cretaceous opened space for mammals to rise, setting the stage for primates and eventually humans.
Action: Based on Earth History Data
From an engineering perspective:
- Establishing the nervous system platform took most of evolutionary time.
- Once in place, scaling through additional neurons happened rapidly.
- We inherit both legacies: the firmware of ancient instincts and the software of flexible cognition.
The lesson is one of legacy: quick evolutionary wins (like insects) can lock species into rigid hardware; slower builds (like vertebrates) leave room for long-term adaptability.
This interpretation rests on ten fixed points in Earth history. While ranges exist, the relative timescales show a clear pattern: the hardest work was building the platform; the leap to intelligence came quickly once it was in place. To see how these numbers come alive through cats, elephants, and humans, step back into the main story of Looking Back in Time.
📖 Series Roadmap
- Forward: A Little Background
- Introduction: Action, Reaction, and the Human Paradox (16.09.2025)
- Looking Back in Time: The Development of the Human Brain (23.09.2025)
- Abstract Senses: Enhancing the way we see the world outside (30.09.2025)
- Bias as a Concept & Climbing the Stairs: Pattern Recognition & Everyday Tasks (07.10.2025)
- Abstract Feelings and Abstract Senses (14.10.2025)
- Motivation (04.11.2025)
- The Social Knowledge Base (11.11.2025)
- Potential (18.11.2025)
- The Subliminal Way We Go Through Life (26.11.2025)
- Taking Responsibility (02.12.2025)
- Fishing for Complements (22.12.2025)
- Peter and Fermi (22.12.2025)
🔗 R&R Navigation
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Endnotes – Looking Back in Time
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