Sometime in the late 1600s, in the lush forests of Mauritius, the very last dodo took its last breath. After centuries of untroubled ferreting in the tropical undergrowth, this species met its untimely end at the hands of humans, who had arrived on the island less than 100 years before. With their penchant for hunting, habitat destruction and the release of invasive species, humans undid millions of years of evolution, and swiftly removed this bird from the face of the Earth.
Since then, the dodo has nestled itself in our conscience as the first prominent example of human-driven extinction. We’ve also used the dodo to assuage our own guilt: the creature was fat, lazy and unintelligent — and as popular story goes, those traits sealed its inevitable fate.
But in fact, we couldn’t be more wrong, said Julian Hume, a paleontologist and research associate with the National History Museum in the United Kingdom. He studies the fossils of extinct species, and has devoted a portion of his career to correcting the dodo’s dismal reputation. By digitally modelling the remains of a dodo’s skeleton, he’s produced a 3D digital reconstruction that draws an altogether different picture of a bird that was faster, more athletic and far brainier than popular culture has led us to believe. “It was nothing like this big, fat, bulgy thing that was just waddling around. This bird was super adapted to the environment of Mauritius,” Hume told Live Science. Instead, humans’ unrelenting exploitation was the real culprit behind the dodo’s untimely death.
But that’s not all we’ve gotten wrong. Despite the commonly held belief, the dodo actually wasn’t the first creature that humans drove to extinction — not by a long shot. In fact, humanity was wiping out the world’s fauna thousands of years before we set eyes on the dodo. “There was certainly a lot more going on before and after that event,” said Hume.
So, if the iconic dodo wasn’t the first species we drove to the brink, then which animal gets this disheartening title, instead?
Humans on the move
We’ve grown accustomed to thinking about human-driven species extinction as a relatively recent trend in our history. Yet, researchers have found convincing palaeontological evidence that dismantles that idea.
“The real problem started when we, as humans, started migrating,” Hume said. That starting point is still debated, but most recent estimates suggest that migrations that led to lasting populations of humans spread across the globe began with the movement of hominids — Neanderthals and other ancient human relatives, as well Homo sapiens — out of Africa and southeast Asia, roughly 125,000 years ago. This is where the evidence gets interesting. As humans left their ancestral homes, and over the following tens of thousands of years went on to colonize Eurasia, Oceania, North and South America, the fossil record shows a parallel uptick in the extinction in large-bodied animals — also known as megafauna — across those continents.
“As [hominids] migrated out of Africa, you see this incredibly regular pattern of extinction,” said Felisa Smith, a professor of ecology and evolutionary biology at the University of New Mexico, who studies how animals’ body sizes have changed over the course of history. As she and her colleagues explained in a 2018 study published in the journal Science, each time our ancestors set foot in new places, fossil records show that large-bodied species — the humongous prehistoric relatives of elephants, bears, antelope and other creatures — started going extinct within a few hundred to 1,000 years, at most. Such rapid extinction timescales don’t occur at any other point in the last several million years (not since the non-avian dinosaurs were wiped out by an asteroid about 65 million years ago.) “The only time you see it is when humans are involved, which is really striking,” Smith said.
Some of those early lost species would seem like fantastical beasts if they roamed Earth today. For example, “There was an armadillo-like thing called the glyptodon, which was the size of a Volkswagen bus,” Smith told Live Science. Glyptodons, many equipped with vicious-looking spiked tails, disappeared from the Americas at the end of the last ice age, roughly 12,000 years ago — which is probably connected to the earlier arrival of humans there. The number of gigantic Eurasian cave bears, several hundred pounds heavier than grizzly bears today, went into a steep decline about 40,000 years ago, around the same time that humans began to spread across their habitat. South America was once home to lumbering giant ground sloths — and humans were also the most likely candidate in their demise, about 11,000 years ago.
What made large animals, in particular, so susceptible to humanity’s spread? Megafauna likely represented food, or a threat, to incoming humans. What’s more, animals that had never encountered humans before were probably unwary of these strange newcomers migrating into their unspoiled lands, which might have increased their vulnerability to attack. Unlike other smaller animals that breed more rapidly, megafauna also reproduce more slowly and so have smaller populations compared with other species, Hume explained: “So if you take out a big section of [a population] they cannot reproduce quickly enough to build up numbers again.”
It wasn’t just hunting that posed a threat — but also the spread of human-caused fires that would have destroyed swathes of habitat, and increasing competition from humans for food. For instance, it’s thought that by preying heavily on the same herbivores, growing numbers of hungry humans helped drive the extinction of the short-faced bear, a gigantic South American species that once stood at over 10 feet (3 meters) tall, and died out roughly 11,000 years ago. Climate change, paired with human impacts like hunting, also proved to be a lethal combination for some megafauna — most famously, mammoths, which went extinct about 10,500 years ago (except for the dwarf woolly mammoth, which survived until about 4,000 years ago on an island off northern Russia). “If you combine climate change with a negative human impact, it’s a disaster,” said Hume.
All of this is to say that humans have systematically wiped out the species around us from almost the beginning of our history. Our migration prompted “a disaster across the world,” said Hume. “We weren’t very pleasant.” Unfortunately, we’ve continued our ancestors’ legacy, with, among thousands of other species, the eradication of Madagascan hippos 1,000 years ago, the loss of moa birds in New Zealand 600 years ago, and the decimation of passenger pigeons 106 years ago. We are also responsible for ongoing extinctions today.
But this still hasn’t answered the question of what species went extinct first. And here’s the catch: the data on human-driven extinction across the planet is only reliable as far back as about 125,000 years— but that doesn’t mean we weren’t driving animals to extinction before that in Africa, too. In fact, there’s compelling evidence to suggest that before humans migrated out, they unleashed their hunting instincts on species there as well.
Smith’s research has revealed that the average body size of African animals 125,000 years ago was only half that of species that were present on other continents around the world. “Africa is one of the largest continents, so it should have had a mean body size similar to that of the Americas and Eurasia where it was roughly about 100 kilograms [220 lbs.],” Smith said. “The fact that it didn’t suggests that there had already been an effect of hominids on megafauna in Africa, prior to 125,000 years ago.”
In essence, because the rest of history tells us that humans are good at dispatching the largest creatures in an ecosystem, we can make a fairly safe assumption that hominids in Africa at the time could have been responsible for extinctions going even further back in time.
Still, there’s no way to know for sure what that ‘first’ species would have been — though Smith takes a wild guess: “It was probably some species in the elephant family. But whether that’s palaeomastodon, or stegodon” — the latter being a behemoth with tusks that measured 10 feet (3 meters) long – “I couldn’t tell you.”
Clues for the future
We may not have a clear answer to that original question – but perhaps the more important one to ask is what humanity’s legacy of extinction can teach us about conservation, going into the future.
Past extinctions have revealed that when animals — especially megafauna — disappear, there are profound ecological consequences. Whole landscapes are transformed in the absence of their shaping effects, with changes to vegetation and species diversity. Smith has even published research showing that the decline of global megafauna in past millennia led to dips in the amount of methane they burped out — with potentially transformative consequences for global climate. What’s more, when animals disappear, whole rafts of dependent species go down with them. The iconic dodo presents one such cautionary tale: when the birds died out, so did a Mauritian dung beetle that relied on dodo feces to survive.
Understanding human-driven extinctions of the past can help us figure out what the environmental consequences have been, explained Smith, and how we can limit those in the future by protecting the species that remain. Even the dodo’s extinction provides clues that are helping us preserve ecosystems today. Hume is working on a project to catalog pollen spores present in the sediments around dodo fossils, to build up a detailed picture of the lush, palm-fringed forests they once roamed. That’s helping conservationists to rewild the island with vegetation that was once there. “We’re actually reconstructing the exact species of plants and trees from the environment the dodo was living in, before humans arrived,” Hume said.
A bit of paradise was lost when we drove the dodo to extinction — not to mention the thousands of species whose demise came before that. But perhaps with hindsight, and the willingness to learn from our mistakes, some of that can be reclaimed.
Originally published on Live Science.
livescience.com, 11 October 2020