When did humans evolve to become fully human?

Artifacts suggest a ‘Great Leap’, a recent appearance of modern intelligence. Fossils and DNA suggest that’s an illusion.

Cueva de Los Manos. Although Neanderthals and Homo erectus may have made simple, abstract art, complex representational art starts appearing only when Homo sapiens became widespread

When did something like us first appear on the planet? It turns out there’s surprisingly little agreement. Fossils and DNA suggest people looking like us, “anatomically modern” Homo sapiens, evolve around 300,000 years ago. However, archaeology- tools, artifacts, cave art- suggest that complex technology and cultures, “behavioral modernity”, evolved more recently, 50,000-60,000 years ago. That’s been read as suggesting the first Homo sapiens weren’t entirely modern. In fact, the different data track different things. Skulls and genes tell us about brains, artifacts about culture. And brains may have become modern first.

The “Great Leap”

For 200,000-300,000 years, human tools and artifacts were surprisingly simple- little better than Neanderthal technology, far simpler than those of modern hunter-gatherers like the Amerindians. Starting about 50-65,000 years ago, more complex artifacts start to appear— complex projectile weapons like bows and spear-throwers, fishhooks, sewing needles. People made representational art- cave paintings of horses, ivory goddesses, lion-headed idols, showing artistic talent and imagination; a bird-bone flute hints at music. Meanwhile, arrival of humans in Australia 65,000 years ago shows we’d mastered seafaring.

This sudden flourishing of technology has been called the ‘Great Leap Forward’, supposedly reflecting the final evolution of a modern human brain. But fossils and DNA hint at an earlier appearance of human intelligence.

“Anatomical Modernity”

Archaic Homo sapiens from Jebel Irhoud, Morocco, 300,000 ya. Jebel Irhoud People had brains about as big as ours, and short faces like Homo sapiens. They had longer skulls and bigger brow ridges. Fossils suggest fully modern human skull shapes evolved between 100,00-200,000 years ago- but given the sparse fossil record, this is a minimum age, not the true age.

Primitive Homo sapiens fossils appear 300,000 years ago in Africa, and had brains as larger or larger than ours. They’re followed by anatomically modern Homo sapiens at least 200,000 years ago, and skull shape became essentially modern by at least 100,000 years ago, at which point, humans had brains similar in both size and shape to ours. Assuming the brains inside were as modern as the box that held it, our African ancestors theoretically could have discovered relativity, built space telescopes, written novels and love songs- their bones say they were as human as we are.

Because the fossil record is so patchy, fossils provide minimum estimates. Human DNA suggests even earlier origins for modernity. Comparing genetic differences between DNA in modern human populations and ancient Africans, it’s estimated that our ancestors lived 260,000-350,000 years ago. All living humans descend from those people. and that suggests that we inherited the fundamental commonalities of our species- our humanity- from them.

All their descendants- Bantus, Berbers, Aztecs, Tamils, Aborigines, San, Han, Maori, Inuits, Irishmen – share certain behaviors absent in other Great Apes. All human cultures form long-term pair bonds between men and women to care for children. We sing, and dance. We make art. We preen our hair, adorn our bodies with ornaments, tattoos, and makeup. We craft shelters. We wield fire and complex tools. We form large, multigenerational social groups with dozens to thousands of people. We cooperate to wage war, and help each other. We teach. We trade. We have morals and laws. We contemplate stars, our place in the cosmos, life’s meaning, what follows death.

The details of our tools, fashions, societies, morals, and spirituality vary from tribe to tribe, and culture to culture, but all living humans show these behaviors. That suggests these behaviors- or at least, the capacity for them- are innate. These shared behaviors unite all of us. They’re the human condition, what it means to be human- and they result from shared ancestry.

We inherit our humanity from people in south Africa 300,000 years ago. The alternative- everyone, everywhere coincidentally became fully human in the same way, at the same time, starting 65,000 years ago- isn’t impossible, but a single origin is more likely.

The Network Effect

Archaeology and biology may seem to disagree, but they actually tell different parts of the human story. Bones and DNA tell us about brain evolution— hardware. Tools reflect brainpower, but also culture- hardware and software. Like upgrading your computer’s OS, technology may evolve even if intelligence doesn’t. Humans in ancient times lacked smartphones and spaceflight, but we know studying philosophers like Buddha and Aristotle that humans were just as clever. Our brains didn’t change, the culture did. And that creates a puzzle.

Middle Stone Age tools, made by early Homo sapiens are more sophisticated than those of Neanderthals- but less sophisticated than those of later Pleistocene people like the Clovis People (Amerindians), and complex tools like spear-throwers and bows appeared only after about 65,000 years.

If Pleistocene hunter-gatherers were as smart as modern people, why did culture remain so primitive for so long- why 150-300,000 years to invent bows, sewing needles, boats? And what changed? Probably, several things happened.

First, we moved out of Africa, occupying more of the planet. There were then simply more humans to invent, increasing the odds of a prehistoric Steve Jobs or Leonardo Da Vinci. We also faced new environments- the Middle East, the Arctic, Indonesia- with unique climates, foods, and dangers, including other human species. Survival therefore demanded innovation.

Many of these new lands were more habitable than the Kalahari or the Congo. Partly, climates were milder, but Homo sapiens also left behind African diseases and parasites. That let tribes grow larger. And larger tribes meant more heads to innovate, remember ideas, more manpower, and better ability to specialize. Population drove innovation.

Humans assemble into vast social networks, like networked computers. The emergent intelligence of towns and cities- thousands or millions of people generating new ideas, behaviors, tools- is vastly greater than a tribe of nomadic hunters. When linked by trade, the processing power of these cultures increases further. Advances in human culture are driven by connections between people, not just individual intelligence.

This triggered feedback cycles. Once new technologies appeared and spread- better weapons, clothing, shelter- human numbers could increase further, accelerating cultural evolution again. Numbers drove culture, culture increased numbers, accelerating cultural evolution, on and on… ultimately pushing human populations to overstrip their environments, devastating the megafauna, and forcing the evolution of farming. Agriculture kicks off an explosive population increase, culminating in civilizations of millions of people. Then, cultural evolution kicked into hyperdrive.

Artifacts are culture, and cultural complexity is an emergent property. That is, it’s not just individual-level intelligence, but interactions between individuals in groups, and between groups, that make cultures sophisticated. Like networking millions of processors to make a supercomputer, we increased cultural complexity by increasing both the number of humans and the links between them.

So our societies and world evolved rapidly in the past 250,000 years; our brains evolved more slowly. We expanded our numbers to almost 8 billion, spread across the globe, reshaped the planet. We’ve done that not by adapting our brains, but by changing our minds. And much of the difference between our ancient, simple hunter-gatherer societies and modern societies just reflects the fact that there’s just lots more of us— and more connections between us.