Who was the first person? Paleoanthropologist Adam Van Arsdale answers one of the most frequent questions we get here at But Why. Also: how does evolution work? Was there a first of every living thing? How did the first animal come alive? How did monkeys turn into people? And what did cavemen eat that we still eat today?
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"Was there a first of every living thing?" - Mira, 5, Philadelphia, PA
"Evolution is all about change over time," Van Arsdale says. "One of the important things to keep in mind about how evolution works is that individuals don't evolve, populations evolve.
"When we're talking about the first humans, we're not talking about one individual who is suddenly very different," he told But Why. "We're talking about a population that maybe became isolated and over time became very different from the other kinds of populations that existed. And eventually we might be able to identify that it became so different we think of it as a different kind of species, or a different kind of animal all together."
There is no first person who we can point to by name or look at the fossilized bones of and say "Eureka! that person is the first human." Van Arsdale is saying that scientists look at a whole population of people over several generations that share the same characteristics and when they see those characteristics, like hands that can hold tools, or bodies that allow us to walk on two feet instead of using our arms and hands to help us walk, they can start to see a new species.
"Who was the first person to live on earth?" - Finn, 6, Beverly, Ma.
Humans are Homo sapiens. Homo refers to our genus, which includes ancient humans like Neanderthals, Homo erectus, and Homo naledi. Sapiens are our species--we're the only Homo sapiens. By looking at fossilized remains of ancient humans and looking at genetic variations, most scientists have determined that our species is pretty recent.
"We probably first appeared as a unique population in Africa about 150,000 to 250,000 years ago," Van Arsdale says.
But there are other ways of thinking about what makes us human. "Our closest relatives on the planet today are chimpanzees and bonobos, two apes that live in Africa today. When did we start becoming something other than an ape?
"The current consensus for scientists is that we share a common ancestor with chimpanzees and bonobos about five to seven million years ago. So sometime around five to seven million years ago a population of this organism started being a little bit different and isolated from the group that went on to eventually become chimpanzees or bonobos. Now this population might have been not the first human in terms of Homo sapiens; it would have been something quite a bit different than us. But it would have been the first step to having some of the traits that we associate with being human today," according to Van Arsdale.
"Modern humans walk on two feet. Chimpanzees and bonobos can walk on two feet, but they can also walk on all fours and climb. "We think, actually, this movement--what we call bipedality, or walking on two feet--was one of the first things that distinguished this early fossil human population five million years ago. And we might not think of them as humans, but the scientific term we have for these earliest things that were on the way to becoming human are hominins. The first hominins appeared as a population about five to seven million years ago, also within Africa, most likely," explains Van Arsdale.
Over time these populations started doing things like using tools and technology and moving outside of Africa, and having bigger brains. Those things happened about two million years ago, that's when scientists think our genus Homo began.
Evolution is not fast. It's not like your grandfather was a monkey but your dad is a human. Each new animal being born is slightly different from its mom and dad. And over time those differences get passed down from generation to generation. We're always changing just a little bit.
Listen to the full episode for more answers to your evolution questions and to find out what cavemen ate (and what the plaque on your teeth might tell future researchers about your diet).
