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What Makes a Human?
What traits set humans apart from every other creature on Earth?

What separates humans from all other animals? It's not just one thing, it's a combination of traits that evolved over millions of years. Your learner will explore what makes humans unique. Things like our big brains, our dexterous hands, our upright walking, and our ability to speak in complex language. These traits didn't appear overnight; they developed gradually in early hominins like Australopithecus. Understanding these foundations helps us see how human evolution is a gradual story of adaptation and change.

S2S_Lesson29 by Selene

Key Ideas

  • Humans are defined by a combination of traits: large brain size, highly dexterous hands, and complex language potential.
  • Humans can speak and share ideas with language.
  • Bipedalism (walking upright) freed hands for tool use, carrying objects, and social interaction.
  • Early hominins, such as Australopithecus, show the beginnings of these defining traits.
  • Human evolution is a branching process; these traits developed gradually over millions of years.

Spines 
  • DK's Science as You've Never Seen it Before: N/A
  • Mammoth Science: Nervous System pg. 62
✏️  Notebooking Activity
List four characteristics that make humans unique. The workbook provides space for learners to write and illustrate each trait.

Cosmic CalendarWhere we are: December 31 · 10:24 PM
The genus Homo appears at 10:24 PM on the Cosmic Calendar. Read the script below before the lesson.

Read aloud: Look at our Cosmic Calendar. It’s 10:24 in the evening on December 31st. We have less than two hours left in the entire cosmic year. Around 10:24 PM, the genus Homo appears, along with the first stone tools, about 2.8 million years ago in real time. Ten thirty at night. That’s when humans arrived. The dinosaurs had 165 million years. Mammals have had 66 million years since the asteroid. Modern humans have had about 200,000 years. We are the newest major story on this calendar, and we’ve already changed the planet in ways nothing before us ever has. That’s worth thinking about.

Timeline EntriesLabel the next page in your timeline “What Makes a Human? 4 Million Years Ago”. The workbook prompt asks learners to draw Australopithecus, like Lucy, walking upright across an African savanna.

Discussion Questions
  1. How do large brains help humans survive and adapt? 
    Sample answer: Bigger brains allow problem-solving, planning, communication, and cultural learning.
  2. Why is dexterous hand function important in human evolution? 
    Sample answer: It enabled precision grip, tool making, and manipulation of objects in complex ways.
  3. What does walking on two legs help humans do? 
    Sample answer: Carry food, tools, or babies and see far away.
Digging Deeper
  • How did language change what humans could do together compared to other primates? 
    Sample answer: Language allowed humans to share knowledge across generations, coordinate complex group activities, pass on cultural innovations, and build on each other’s ideas — creating a kind of collective memory no other animal has.
  • How does having a larger brain affect other aspects of being human? 
    Sample answer: Larger brains require more calories, driving humans to find more reliable food sources. Babies are born with underdeveloped brains that need years of nurturing, this extended childhood is what makes human culture and learning possible.

Vocabulary
  • Hominin — The group that includes modern humans and our extinct relatives and ancestors, such as Australopithecus and Homo erectus.
  • Bipedalism — Walking upright on two legs; a defining feature of hominins that freed the hands for tool use and carrying.
  • Australopithecus — An early hominin that lived 2-4 million years ago in Africa; had bipedal posture but a smaller brain than modern humans.
  • Dexterity — Skill and precision in using the hands; human dexterity allows us to make tools, write, and perform complex tasks.
  • Language — A system of communication using sounds, symbols, or gestures; complex language is one of the most defining human traits.
  • Cranial Capacity — The volume of the skull, used as an estimate of brain size; human cranial capacity is much larger than other primates.
  • Tool Use — The ability to use objects to accomplish tasks; humans create complex tools from scratch, unlike any other animal.

SCIENTIST SPOTLIGHT: Zeresenay AlemsegedZeresenay Alemseged is an Ethiopian paleoanthropologist who discovered one of the most extraordinary fossil finds in the history of human origins research. In 2000, working in the Dikika region of Ethiopia, his team found the nearly complete skeleton of a young Australopithecus afarensis child who lived 3.3 million years ago. The child, nicknamed Selam, had a small brain but also had features suggesting she could walk upright. She also retained some features associated with tree climbing, giving scientists a detailed picture of an ancestor that was neither fully ape nor fully human but something in between. Alemseged grew up in Ethiopia, was educated partly in Europe, and has dedicated his career to studying human origins on the continent where they actually happened.

Videos:Website:
Digging Deeper Activity:
Compare a labeled diagram of a chimpanzee skeleton, an Australopithecus skeleton, and a modern human skeleton. What changes do you notice in the pelvis, leg bones, and skull? What do those changes suggest about how each species moved and lived?

Species to ResearchThis lesson covers early hominin species. Here are some human relatives learners can choose to research:
  • Homo habilis— One of the earliest members of the genus Homo; associated with the first stone tools made about 2.4 million years ago.
  • Homo erectus— A long-lived hominin species that spread from Africa into Asia; the first hominin known to have left Africa.
  • Homo neanderthalensis (Neanderthal)— A close relative of modern humans who lived in Europe and Asia; evidence shows they buried their dead and made art.
  • Denisovan— A mysterious hominin known mostly from DNA evidence; they interbred with both Neanderthals and early Homo sapiens.
  • Homo heidelbergensis— A species considered ancestral to both Neanderthals and modern humans; had a large brain and made advanced hand axes.

Sources

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