The Mythical March of Progress
Even if you don’t know the name ‘The March of Progress’, you’ll undoubtedly recognise the image - fifteen of our evolutionary ancestors lined up as if they are marching from left to right across the page, from knuckle-dragging monkey to upstanding modern man.
And even if you haven’t seen the original, which was first published as a four-page fold out in the ‘Early Man’ volume of ‘Life Nature Library’ in 1965 - then you’ll definitely have seen a parody, either printed on a T-shirt or mocked up in a TV show.
The pictures, which were drawn by natural history artist Rudolph Zallinger, were intended to give an accessible overview of 25 million years of human evolution. Zallinger may have been inspired by Thomas Henry Huxley's 1863 illustration in ‘Evidence as to Man's Place in Nature’.
Huxley’s images were intended to simply compare the skeletons of apes and humans, but making them walk across the page from left to right format led people to believe it represented the evolutionary transformation of monkey into man.
Zallinger’s original March of Progress, via Wikimedia Commons
The image captured popular attention and was widely reproduced thanks to the fact that it was easy to understand and told a simple but memorable story about our human origins.
Today, the March of Progress is probably one of the most widely recognised scientific images, and it’s an instantly recognisable short-hand for evolutionary progress. And like every other viral phenomenon, it has been widely reinvented and parodied by everyone from surfers to The Simpsons.
Mike Keefe’s evolution of communication is probably my favourite version, showing us changing from ape-like early humans carving our first words in stone, to sophisticated gentlemen reading books, back to ape-like creatures tweeting from our phones. It’s even been used to display the improvement of iPhones over successive models.
But unlike iPhones, humans were not created in a series of models, each with better specs and a more advanced camera, with each previous version becoming obsolete and extinct. Our evolutionary journey was far from straightforward - as were the paths taken by our hominid ancestors as they evolved into our modern-day ape relatives.
Zallinger’s simplistic picture of progress has therefore come in for increasing criticism over the years, as our scientific knowledge about human origins has grown. People saw the image and may have interpreted it as each early human neatly morphing into the next ‘more sophisticated’ upgrade, with the earlier model becoming extinct as a result.
And we can maybe put the blame for a common creationist trope onto his picture too: “If we came from monkeys, why are there still monkeys?”
To be fair to Zallinger, he apparently never meant to imply that the evolution of man was a linear process. His captions even labelled some species as side branches and evolutionary dead ends, and the accompanying timelines in the book certainly didn’t suggest direct continuity between species.
Unfortunately, as the book’s author F. Clark Howell put it: ‘The graphic overwhelmed the text. It was so powerful and emotional’. So, it seems that evolution has not yet gifted us ‘advanced’ humans with the ability to read captions before jumping to conclusions.
If the March of Progress is a misleading representation of human evolution, what should it really look like? To find out, I spoke to Chris Stringer, a research leader in human origins at the Natural History Museum in London.
The truth is that human evolution was undoubtedly a messy affair. Chris told me that we’re still not really sure how it happened, but we have learned a lot since Zallinger’s illustration was published. And there’s been a cascade of developments over the last ten years, thanks to new fossil discoveries, advanced DNA sequencing, and protein analysis technologies.
According to Chris, one of the most important things we’ve learned over the past decade is that there was diversification during human evolution, and even within the last hundred thousand years there were five kinds of humans living on the planet.
So if he got to re-draw the iconic March of Progress, what should it look like?
Chris: Well, it would be a rather than a tree trunk going up to a single, peak at the top, it's going to be a tree that's diversifying and the branches are mixing in now and again with each other. So, it's a complex... you could call it a web, you could call it a network.
But who are these mysterious humans in our ancient social network?
Well, researchers think our ancestral line split into three about 1.5 million years ago, producing Homo sapiens in Africa, the Neanderthals in Eurasia, and a recently discovered species called Denisovans in Asia.
While the Neanderthals are relatively well known, scientists discovered the Denisovans in 2010, when they found an ancient finger bone in a cave in Siberia with DNA that was neither Neanderthal nor modern human.
Scientists have also found Denisovan remains in a cave in China, showing that the species must have been widespread. Researchers now believe that other fossil finds previously identified as Homo sapiens or Neanderthal may actually be Denisovan after all.
These three human species co-existed in different locations around the globe for around 400,000 years until Homo sapiens began to venture out of Africa, ultimately resulting in the demise of these other early humans.
But this isn’t even the whole story. Recent fossil finds have confirmed that other early humans co-existed with us at the same time as the Neanderthals and Denisovans.
In 2003, archaeologists uncovered the remains of a tiny person, nicknamed the Hobbit, on the island of Flores in Indonesia. The species, now called Homo floresiensis, appears to have evolved there in isolation for over a million years before Homo sapiens moved in.
Then in 2015, anthropologists discovered another early human species in the Rising Star cave system in South Africa. Named after the local language word for star, Homo naledi had a brain no bigger than a gorilla’s, leading us to believe it was a primitive human.
However, it appears the Naledi placed their dead into the cave on purpose. This apparent sophistication, combined with the fact that they lived in an area populated by Homo sapiens makes them very difficult to place in the history of human evolution.
Chris Stringer thinks there are yet more species of ancient humans that are yet to be discovered. He estimates that 90% of Africa was inhabited by people who left behind stone tools for us to find, but we only have fossils from relatively small areas.
What’s more, we only have one ancient human fossil from the entire Indian subcontinent. So, what we’ve learned in the last ten years is probably just the tip of the iceberg, and there is much more to come.
There were definitely other species of humans around on prehistoric earth. And there’s plenty of evidence that these species didn’t keep themselves to themselves.
Although the arrival of Homo sapiens in new areas eventually spelled doom for any other humans in the area, there is mounting evidence that we not only lived alongside other humans before their extinction, but we also interbred with them.
The result of these ‘get togethers’ is that our modern genomes contain snippets of DNA from these other ancient humans. Most of us with European ancestry have around 2% Neanderthal DNA, and people of East and Southeast Asian descent also have Denisovan DNA within their genome.
Most incredibly, in 2018, ancient DNA researchers Viviane Slon and Svante Pääbo announced that they had discovered the remains of female who had died around 90,000 years ago in a Siberian cave whose mum was a Neanderthal and whose Dad was a Denisovan.
But that’s not all. Geneticists have found evidence of other ‘ghosts’ in the human genome left from long-lost ancestral species that we haven’t even discovered yet. While you might feel uncomfortable at the idea of having genes from human ancestors that we drove extinct hanging around in your genome, it might actually provide some benefits, which explains why these sections of ancient DNA have survived.
The bits of Neanderthal DNA that persist in the modern human genome may help our immune systems, they may give us the ability to digest lactose, and also contribute to the pale skin pigmentation found in Europeans. And Denisovan DNA may help mountain-dwelling Tibetans survive life at high altitudes.
Unfortunately, it’s not all good news, and researchers think that some of this ancient DNA is associated with an increased risk of conditions like diabetes, autism and depression.
The sciences of genetics, anthropology and palaeontology have transformed our understanding of human origins. We’ve come a long way since the simplistic March of Progress, and there’s still a lot of work to do to untangle the complex web of interactions between ancestral species on the journey towards modernity.
Our ancient dalliances may have left a lasting trace within our DNA, but all these archaic species are long gone, so why should we care about them? Who cares about how we evolved? Surely what’s important is that we’re here now?
For Chris Stringer, mapping out the origins of humanity not only tells us about where we’ve come from and helps us understand our place in the natural world, but it can also help to reveal where we might be going as our planet continues to change around us.
Chris: If global warming reaches the worst state that some people predict, then our planet is going to change more than humans have ever known before. And that's going to have a huge impact on our evolution.
And I think, if the tropics and subtropics become essentially uninhabitable for humans, you're going to end up with small numbers of humans close to the North pole and the South pole doing their best to survive. That's going to drive our evolution in completely unpredictable ways. Let's hope it doesn't go that far. My fear is that that may be the future of humanity.
References and further reading
Washington University in St Louis - ‘On the Origins of “The March of Progress”’
Nature - ‘Biggest Denisovan fossil yet spills ancient human’s secrets’
New Scientist - ‘Traces of mystery ancient humans found lurking in our genomes’
Mum’s a Neanderthal, Dad’s a Denisovan: First discovery of an ancient-human hybrid - Nature
