Where did we come from?
There’s something about human evolution that’s inherently intriguing; it stirs an innate curiosity about what came before (and lived and died and bred with) our species, Homo sapiens.
But where in our ancestry does the “human” part of “human evolution” begin?
In other words, how far back in time must we go for our ancestors to not be human and be, instead, an ape walking on two legs? What’s needed to qualify as “human”?
Getting to the bottom of this is more complicated than it appears, says Tanya Smith, a human evolutionary biologist at Griffith University.
More than a century ago, scientists began classifying fossils depending on whether they appeared to have looked and acted more in line with humans living today — that’s us — than ancient hominins, such as the ape-like Australopithecus afarensis, nicknamed Lucy, which lived a few million years ago.
“Originally it was things like brain size, tool use — what we thought of as hallmark specialisations of humanity that would be different from earlier Australopithecines,” Professor Smith says.
In the years since, though, fossil discoveries overturned some of those assumptions.
So where are we at?
Let’s start with the here and now. We, Homo sapiens, are in the human bucket — we define what is human.
We’re backed up by the Macquarie Dictionary, which states a “human” is “a human being”, which, in turn, is “a member of the human race, Homo sapiens“.
Contrary to the Macquarie Dictionary, though, we’re not alone in the historical human bucket.
So, let’s take a whistlestop tour of our evolutionary history and see where we end up.
Our closest cousins
Travel back in time a few tens of thousands of years, and there were other two-legged primates that looked a lot like us getting around the planet.
They included our closest cousins Homo neanderthalis, better known as Neanderthals, and a group some consider a sister lineage of Neanderthals called the Denisovans.
Skeletons show Neanderthals were muscular and a bit shorter than us, but had a bigger brain for their size. The Denisovan portrait is fuzzier — the entire reported suite of Denisovan fossils could be counted on two hands — but they likely resembled Neanderthals.
We don’t know a huge amount about Neanderthal behaviour, but what’s increasingly clear is they weren’t the knuckle-dragging, club-wielding oafs depicted in popular culture.
They made tools and art and engaged in symbolic behaviours, creating objects that had uses beyond consuming food.
“You can find … teeth that had been pierced potentially for wearing or adorning things, and these are from sites that were really strongly associated with Neanderthals,” Professor Smith says.
“So it does seem like some basic abstraction and symbolism was practised, at least by the later Neanderthals.”
Whether those behaviours originated within Neanderthal groups or were copied when they came in contact with Homo sapiens, we don’t know, Professor Smith says.
Alongside fossils and other archaeological remains, traces of Neanderthals and Denisovans are found today as stretches of DNA in our genome, remnants of interbreeding through the ages — not just with us, but with each other too.
So, Professor Smith says, instead of thinking of our species’ evolution as a “family tree” — with branches splitting into two species, then going on to split again or become a dead end — think of it more like a braided river, where multiple water channels diverge, flow for a bit, then come back together.
“It’s the idea of genetic information potentially mixing in some populations, then splitting, then later in time mixing again and splitting again.”
These ancient encounters prompted some researchers to suggest the three types of human should be considered the same species, Australian National University evolutionary biologist João Teixiera says.
What’s in a name?
Could the answer to our question be as simple as nomenclature?
The Homo part of our and Neanderthals’ Latin name means “human” or “man”. Over the decades, more members have been added to the Homo genus, such as Homo floresiensis, perhaps better known as “The Hobbit”, and Homo naledi.
So would the first human be the first Homo?
Well … maybe, La Trobe University archaeologist Andy Herries says.
“If we define something in the genus Homo, then we’re defining that it is fundamentally more like us.
And yet, this is not without controversy.
“Strictly speaking, the oldest fossil that has been included in the genus Homo is 2.8 million years old from Ledi-Geraru in Ethiopia,” Professor Herries says.
“But lots of people disagree entirely with that assessment. It’s half a mandible.”
What about cultural practices, like burying their dead, or symbolic representations?
“The behavioural evidence is spotty,” Professor Smith says.
“From that period, they were using tools, but we don’t know that they were using fire, and certainly we don’t think we’re burying their dead or creating symbolic representations of things.
“It’s not ’til much later in the record that we would get some of the things that we think of as contemporary behaviours.”
The likely “first human”, she says, was Homo erectus. These short, stocky humans were a real stayer in human evolutionary history.
Estimates vary, but they’re thought to have lived from around 2 million to 100,000 years ago, and were the first humans to walk out of Africa and push into Europe and Asia.
They’re credited with abstraction, as evidenced by an engraved shell some half a million years old.
Neanderthals, H. sapiens and Denisovans are considered by some to have evolved from H. erectus populations in different parts of the world: Neanderthals in Europe, H. sapiens in Africa, and perhaps Denisovans in Asia.
Case closed, right?
Well … even this is tricky, because there’s an older Homo than H. erectus.
Meet Homo habilis, or “handy man”, named because fossil remains were found near a plethora of stone tools.
It appeared on the scene around 300,000 years before the earliest known H. erectus, and its placement in the Homo genus has been contentious, to say the least.
Some researchers suggest it’s ape-like enough that it should be shifted to the more ancient Australopithecines, which would strip it of its human or Homo name.
By this point, we’ve travelled a couple of million years back in human history. Fossilised remains from around the time and earlier are incredibly rare, and what is unearthed tends to be in bits.
“Rarely do you get a full suite of evidence in a single individual. So you’ll get a bit of a skull, and then you’ll get a bit of a hand and you’ll get a bit of a pelvis and you get a couple teeth, but we don’t know how they knit together,” Professor Smith says.
“It’s only later in the fossil record that we have good, full remains from a single Homo erectus.
“Then you have sites where we know we had multiple individuals living at the same time, but [the fossils and artefacts] don’t come with labels when you get them out of the ground.”
Plus there’s the gradual nature of evolution itself, Professor Herries says.
“There are so many different aspects of what makes us human, but they don’t all arrive at the same time — that never happens.
“[Walking upright] usually comes first, then potentially stone tools, and then we get big brains, which should be no real great surprise because stone tools allow you to access a much wider range of resources, and that helps your brain get bigger.”
So, while there’s no absolute line in history with humans on one side and apes on the other, Professor Herries agrees the first human by contemporary measure was likely a Homo erectus.
“There was a big evolutionary step that happened at about 2 million years to 1.8 million years, at that switch to Homo erectus, that moves towards more complicated stone tools and behaviour. They were the first global travellers.
“They did a lot of things for the first time.”