Extinction of nature's giants tracks human expansion across the globe

Irish Times

09-06-2025

When did humanity's destructive
relationship with nature
begin? Was it the unleashing of neoliberal market reforms in the 1980s? Was it the dawn of the Industrial Revolution in the late 1700s? Or even the beginning of the era of capitalist colonialism in the late 1490s?
Or does it go back further, to the rise in agriculture, or organised religion that granted on to men dominion over all the beasts of the earth? While these are all important points of inflection in our troubled relationship with nature, none point neatly to a juncture where peaceful harmony gave way to something darker in the human spirit.
Last year,
a fascinating paper
published by a team from Aarhus University in Denmark, tells the remarkable tale of early modern humans and their relationship with the giants that had, up to then, ruled the land for millions of years. Large animals, referred to as 'megafauna', dominated terrestrial ecosystems in a way that is hard to imagine today.
For instance, there are only three species of elephant in Africa and parts of southern Asia, but until quite recently, 12 other elephants roamed throughout Europe, the Americas and across Asia as far as the high Arctic. There were
distinct species
of dwarf elephants living on islands, including off the coast of California and in the Mediterranean, including Cyprus and Sicily (later, the unearthing of their skulls would inspire myths of the Cyclops).
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Many of these mammoths and mastodons were huge, well over 1,000kg, but they were not alone. There were 16 types of ground sloths (one nearly as tall as a modern African elephant), giant marsupials in Australia, an armadillo the size of a small car in South America and an American beaver twice the size of those that exist today.
Then there were the carnivores: sabre-toothed cats, dire wolves and cave bears (both substantially bigger than their surviving relatives). There were lions and rhinos across Europe and America. The world was also inhabited by monster birds, including the flightless moas in New Zealand, some up to 3m in height, and Haast's eagle, the largest eagle ever to have existed, up to twice the size of the largest eagle in existence today.
Due to their large size and abundance, the megafauna shaped the ecosystems in which they lived, but today they are nearly all gone. From 50,000 years ago, their signature in the fossil record starts to flicker out. Today, only 11 out of 57 species weighing in at more than one tonne survive, while nearly half of the animals in the 100-1,000kg size range also disappeared. The researchers from Aarhus refer to this 'simplification' of the fauna as 'unique on a 30 million-year timescale.'
When the bones of the megafauna started to be unearthed by European scientists in the 1700s, they caused bafflement. Extinction was not an accepted concept at the time, indeed, it was heretical to believe that God, after creating a perfect world, would allow any of his creations to disappear.
Thomas Jefferson, third president of the United States, fervently hoped that America's elephant, the mastodon, still roamed the western parts of the Continent which were then unknown to white people. As evidence grew from around the world, and it became clear that extinction was a real phenomenon, investigation into the vanishing of the megafauna narrowed to two prime suspects: changing climate or 'overkill', the idea that early hunter-gatherers hunted the great beasts off the face of the earth.
However, that debate now seems to be settled, with the Danish researchers finding that 'there is little support' for the climate-driven theory'. There are two principal reasons which point the finger at humans: first, the extinction was heavily biased towards the largest animals on land, smaller animals were much less affected while plants, and animals in the ocean, not at all.
Second, the time frame over which extinctions occurred tracks closely the expansion of humans across the world's land bodies. Africa, where the human story begins, is not so much affected (though it doesn't escape completely). But as people spread to Asia, Europe and Australia, the giants fell. In the Americas, dates for extinction match the arrival of people 15,000 years ago, while the moas and Hast's eagle survived in New Zealand up to human colonisation in the 1400s.
Jens-Christian Svenning is the lead author of the paper and believes that rather than looking at the megafauna extinctions as an 'event', it is instead 'the start of humanity's transformation of the biosphere', something that continues to this day.
Populations of surviving megafauna are in a 'dire state' says his paper and nearly half of all mammals today weighing more than 10kg are threatened with extinction. He notes that 'it's a process that likely has very deep roots, the start of it is probably a million years ago but became really apparent from about 50,000 years ago'.
That humans are the cause can still stoke debate, but at this stage, Svenning seems confident to brush this off. 'To be completely honest, the relation to humans, and the lack of a consistent relationship to climate, is a very clear pattern. From that perspective, it's weird that it's still controversial ... People undervalue how resourceful and impactful hunter-gatherer people have been.
'In Europe, there is a strong tendency to interpret the ecosystems before agriculture as natural, implying that people hardly had any influence on their environment before that. But people 50,000 years ago were just as capable as we are ... there's no reason why they wouldn't try to manipulate their environment for their own benefit ... the ideal of the 'noble savage' is still quite prevalent.'
Svenning notes that at the scale of a human lifetime, extinctions happened over a very prolonged period (woolly mammoths survived in Siberia right up to 4,300 years ago) so people were likely unaware of the impact of their actions, something that can't be said for us today.
Humans and our ancestors have been hunting large animals for a long time, and possibly precipitated extinctions even before the arrival of modern humans. 'It's well established that Neanderthals killed straight-tusked elephants in Europe,' he points out, however their impact was limited due to their small population sizes (it is also notable that Neanderthals also went extinct with the rise of Homo sapiens). Human impact was not related, therefore, only to their capabilities, but to their expansion in numbers.
The consequences of the absence of large herbivores, which play key roles in seed dispersal, spreading of nutrients and the structure of vegetation, have been profound. Less grazing has meant more growth of woody plants, which, depending on the climate, leads to more fires, a pattern that is perpetuated to this day with the absence of large grazers that were common even a few centuries ago. As for the impact on climate, the picture is complicated as multiple effects are likely to have had warming and cooling effects.
Today, wild animals only make up a mere 4 per cent of the total mass of mammals in the world. Today's megafauna is mostly made up of cattle and other domestic animals and there have been suggestions from some in the livestock industry that the overall effect on the planet is neutral.
However, today's 1.5 billion cattle, many of which are confined for some or all of their lives, eating processed foodstuffs and prevented from displaying their natural behaviours, are no substitute for healthy natural ecosystems.
Whole processes, driven by a fantastic diversity of animals, such as migration, predation, seed dispersal, decomposition and scavenging, are now absent from swathes of Earth's land surface.
'I'm pretty sure we have a lot more livestock now, and a lot more [methane-emitting] ruminants than there were wild animals in the past,' says Svenning. 'The way we keep the livestock is completely non-analogue to naturally living megafauna, there's no doubt it's not comparable.
'If one wanted to have more sustainable livestock production from a climate and biodiversity perspective, the way to go is low intensity, low stocking rates, such as in European semi-natural landscapes, that's very possible. Of course, the consequence of this is that the production is much, much lower. So, it means there won't be so much meat available for everybody to consume. That's simply impossible.'