What Makes Us Human? The Traits That Set Us Apart

"What makes us human?" sounds like it should have a tidy answer — one gene, one organ, one spark. It does not. Every trait we like to claim as ours alone turns out to be either shared in some form with other animals or already present in extinct members of our own family, the hominins. We are, biologically, one species of great ape, sharing roughly 98.8% of our DNA with chimpanzees. And yet the distance between a chimpanzee troop and a human civilisation is staggering.

The honest answer is that our species is defined by a package of features that evolved at very different times, layered one on top of another. Walking upright is millions of years older than our big brains; big brains are far older than art or agriculture. Below is a quick map of when each defining trait appeared, followed by a closer look at each one. If you want to see how these traits are distributed across our relatives, the interactive species comparison tool and the species profiles are good companions to this guide.

Walking upright (bipedalism)

The oldest thing that makes us human is not in our heads but in our hips. Habitual bipedalism — walking on two legs as our normal mode of getting around — is the earliest defining trait of the hominin line, and it predates every other item on the list by millions of years.

The evidence runs deep. Sahelanthropus tchadensis from Chad, dated to around 7 million years ago, has a skull whose spinal opening sits underneath rather than behind it, hinting at an upright posture. Ardipithecus ramidus ("Ardi"), about 4.4 million years old, combined a grasping big toe for climbing with a pelvis reshaped for upright walking. And at Laetoli in Tanzania, a trail of footprints pressed into volcanic ash about 3.6 million years ago — most likely made by Australopithecus afarensis, the species of the famous "Lucy" — records a strikingly human, heel-to-toe stride, with no knuckle-print in sight.

Why did it matter? Walking upright freed the hands from locomotion. Hands that no longer had to bear weight could carry food, infants, and eventually tools. It reshaped the pelvis, spine, legs and feet, and it set the stage for everything that followed. Crucially, it came first — long before brains enlarged. For the deeper story, see why humans started walking upright.

Big, reorganised brains

The trait most people name first is the brain — and it is genuinely extraordinary, but not in the simple way it is often told. Early australopiths had brains of roughly 400–500 cc, only a little larger than a chimpanzee's (~350–400 cc). Over the next two million years, brain volume climbed: Homo erectus reached around 900 cc, and modern Homo sapiens average roughly 1,350 cc. (Neanderthals, notably, averaged about 1,400 cc — larger than ours, which is why size alone cannot be the whole story. See our piece on Neanderthal vs human brain size.)

What matters is not just bulk but reorganisation — how the brain is wired. Human brains show expanded association areas, particularly in the prefrontal and parietal cortex, and distinctive connectivity that supports planning, language and abstract thought. This tissue is metabolically expensive: the brain is about 2% of body weight but consumes around 20% of our resting energy. The "expensive-tissue hypothesis" proposes that our ancestors could afford such costly brains partly by evolving a smaller gut, aided by higher-quality food — meat, and later cooked food. Which points straight to the next trait.

Tools and technology

Tool use itself is not unique to us — chimpanzees fish for termites with stripped twigs, and crows bend wire. What is unique is cumulative stone technology that improved over time. The oldest known flaked stone tools, the Oldowan industry, date to about 2.6 million years ago (with contested older cut-marks and the Lomekwi tools claimed at ~3.3 million years). Oldowan tools are simple: a cobble struck to produce a sharp flake for cutting hide, meat and plants.

Around 1.7 million years ago the Acheulean arrived, defined by the teardrop-shaped handaxe — a tool made to a mental template, worked on both faces, and produced with remarkable consistency for over a million years. Later, the Middle and Upper Palaeolithic brought prepared-core methods, blades, hafted points, bone tools, needles and spear-throwers. Each stage built on the last. The key point is not that we made tools but that our toolkits accumulated complexity no other animal can match. Fire belongs in this story too; you can read about the control of fire as one of the most transformative technologies of all.

Language and symbolic thought

Language may be the trait that feels most essentially human — the ability to combine a finite set of sounds into an infinite range of meanings, and to talk about things that are absent, abstract or imaginary. But language leaves no direct fossils, so we infer it from proxies: symbolic artefacts and, cautiously, from genetics.

Here it is worth being careful about FOXP2, often mislabelled "the language gene." FOXP2 is a regulatory gene, and mutations in it genuinely disrupt speech and language in affected families. But it is not a stand-alone language switch: versions of FOXP2 exist across mammals and birds, where it is involved in vocal learning and motor control. Early-2000s claims that a distinctively human FOXP2 variant had been under strong recent selection were later complicated when Neanderthal genomes showed they shared the same protein-coding changes, and follow-up work questioned the original signal of recent selection. Language is built from many genes plus brain organisation — not one gene. You can explore FOXP2 and other molecules of the human story in our 3D protein viewer.

The archaeological signs of symbolic minds are firmer: engraved ochre from Blombos Cave in South Africa (~75,000–100,000 years old), pierced shell beads worn as ornaments, pigment use, and deliberate burial. These are traces of minds that trade in symbols — things that stand for other things — the same capacity that underlies language, art and religion.

Culture that accumulates (the ratchet effect)

If one candidate comes closest to being the human difference, many researchers point here: not tools or language in isolation, but cumulative culture. Other animals have traditions — chimpanzee groups have distinct nut-cracking and grooming customs. But those traditions rarely improve across generations. Ours do, relentlessly.

Psychologists call this the ratchet effect: humans copy existing know-how with high fidelity, occasionally improve it, and pass on the improved version — which then becomes the new baseline. Like a ratchet, culture holds each gain and rarely slips back. No single person could design a smartphone, a vaccine, or a written language from scratch; each is the compounded product of countless minds across time. This depends on high-fidelity social learning, teaching, and language working together. It is why a species that is physically weaker than a chimpanzee can reshape the entire planet. Arguably, the real answer to "what makes us human" is less any one trait than this capacity to stand on the shoulders of everyone who came before.

Small anatomical tells

Beyond the headline traits, our skeletons carry a set of quieter signatures — features anatomists use to tell modern humans apart from other apes and extinct hominins:

• Reduced canines. Unlike other apes, we lack large, projecting canine teeth — a change that appeared early in the hominin line and hints at shifts in diet and social conflict.
• A bony chin. Homo sapiens is the only hominin with a true projecting chin; even Neanderthals lacked one. It is a reliable "us" marker on a jaw.
• A globular skull. Our braincase is high, rounded and globe-shaped, unlike the long, low skulls of Homo erectus and Neanderthals — a difference in brain shape, not just size.
• Prolonged childhood. We grow up slowly, with an extended period of dependency and learning that gives culture time to be transmitted.
• A precision grip. Our opposable thumb and reshaped hand allow fine manipulation — threading a needle, knapping a blade — that underwrites our technology.

None of these alone makes us human, but together they form a recognisable modern-human pattern that emerges clearly by about 300,000 years ago in African fossils like those from Jebel Irhoud, Morocco.

So what actually makes us human?

Pull the threads together and the tidy, single-spark answer dissolves. Bipedalism is millions of years older than our genus. Tool use exists in crows and chimps. Large brains were matched or exceeded by Neanderthals. FOXP2 is shared with other species. Even symbolic behaviour may have flickered in our cousins. No individual trait is uniquely, exclusively human.

What is unique is the assembly: an upright body with free, dexterous hands; a large, heavily reorganised and expensive brain; a capacity for open-ended language and symbolic thought; and — binding it all — cumulative culture that lets knowledge compound across generations rather than reset each lifetime. Being human is an emergent property of that whole system, built piece by piece over seven million years. We are not the endpoint of a march toward perfection; we are the one surviving twig of a once-bushy family tree that happened to inherit, and combine, this particular set of tools. That, more than any single trait, is what makes us human.