Sixth Extinction

A dodo skeleton cast and a dodo model standing next to each other in a museum
Image Source: BazzaDaRambler

Everyone’s favourite naturalist, Sir David Attenborough, returns to our screens tonight with a brand-new one-off documentary. Called Extinction: The Facts (a follow-up to last year’s Climate Change: The Facts), it will look at how human population growth, rampant over-consumption, the illegal wildlife trade, climate change, overfishing, pollution, and land-use change are all driving the loss of biodiversity across the world.

While I’m sure the show will be a fascinating one-hour, it will probably make for gloomy and uncomfortable viewing. But programmes like this are crucial to explaining to huge audiences around the world how human activity causes extinction, why we haven’t acted sooner, and what we can do to help moving forward at this critical turning point in the Earth’s history.

Extinction Events

Extinction is a fact of life – a natural and necessary consequence of evolution. It explains why dinosaurs, trilobites, sabre-toothed cats and mammoths no longer share our planet with us. Just as every individual that is born will die, every species that evolves will eventually become extinct. Some species may give rise to descendants through the process of evolution as the environment changes around them. Others, however, may vanish without a trace, leaving no line of descent whatsoever.

Most of the time, extinction is fairly consistent – as one species dies out, another is born. But during the history of Earth, there have been several periods where extinctions occurred at significantly elevated levels. These are called extinction events.

The most famous of these happened 66 million years ago, when the dinosaurs and various other giant reptiles, which had dominated for over 150 million years, were wiped out in the geological blink of an eye. It is generally believed that a huge asteroid, 10 to 15 km wide, hit the planet, devastating the environment. Immense clouds of dust and gases created by the impact rose into the air and not only caused killer storms and acid rain but also shrouded the atmosphere and blocked out the sun. This halted photosynthesis in plants and plankton, causing catastrophic long-term effects on food chains. The climate cooled drastically and probably remained so for at least a decade. Very few land-living animals weighing more than 25 kg survived.  

A reconstruction of a Tyrannosaurus rex, or T-rex
This is a reconstruction of a Tyrannosaurus rex, one of the last species of dinosaur living on Earth before the cataclysmic asteroid impact. The only lineage of dinosaurs to survive this extinction event were the birds.
Image Source: ScottRobertAnselmo

But the extinction event that heralded the end of the dinosaurs was not the first to have occurred in our planet’s history. At least four other mass extinctions happened before that. The largest and most severe occurred around 252 million years ago, as the Permian Period transitioned into the Triassic. This event – also known as the ‘Great Dying’ – wiped out 70% of terrestrial vertebrate species and a staggering 96% of all marine species. This was the end of the sea scorpions, the trilobites, and other strange creatures that look like nothing alive today. Because so much biodiversity was lost, the recovery of life took significantly longer than any other extinction event, possibly up to 10 million years. No one knows for certain what caused it, although one or more large meteor impact events, massive volcanic eruptions and/or climate change brought on by large releases of underwater methane have been suggested.

The Extinction Rate

So it should now be abundantly clear that species are not eternal. In fact, some 99.9% of all species that have ever lived are now extinct. The natural ‘background extinction rate’ is believed to be one or two out of every million species disappearing per year – so slow that speciation and extinction more or less equal out.

But if extinction really is a natural process, why should we get so worked up about it? Does it matter if we lose a few species here and there?

Imagine that a massive ancient stone building is equivalent to all life on Earth. Each brick represents one species. If you remove a small number of bricks at random, the building will probably survive with few negative effects (although it will, at the very least, be aesthetically worse off). However, if you remove enough bricks without replacing them, the entire structure will fall. Last year, a landmark report found that up to one million species of plants and animals face extinction, many within decades, because of human activity. That is an awful lot of bricks.

Just as it is clear that removing the bottommost bricks in this hypothetical building would hasten the structure’s collapse, we can reasonably speculate that certain extinctions in the natural world – of important keystone species that are vital to food chains or habitat health, for example – would have untold catastrophic effects on the many other plants and animals that, directly or indirectly, depend on them. But even if only the ‘less important’ species died out, there is still a point of no return beyond which entire ecosystems would collapse, and we cannot be so arrogant as to assume we know where that point is – because the simple fact of the matter is that we don’t. The full complexity of the vast web of the interconnectedness of nature is so beyond our current comprehension that we cannot predict with any real certainty the effects of the damage to any particular part of it.

The Sixth Extinction

Extinction events have punctuated the history of life on Earth. It is often said that the last one to occur was the one that wiped out the dinosaurs. But we are, in fact, in the middle of one right now. It is called the Sixth Extinction.

The Earth has entered the Anthropocene, a new human-dominated geological epoch. As early humans moved across the planet, the majority of the large animals – the megafauna – that happened to live in the areas that we occupied vanished. Although climate change following the end of the last Ice Age and fragmented populations may have weakened these species of megafauna, it is becoming clear that, in most cases, our ingenuity and appetite drove them to extinction. Gone are the huge ground sloths of South America, the giant kangaroos, marsupial lions and hippo-sized wombats of Australia, and the mammoths, woolly rhinos and dire wolves of the Northern Hemisphere. The only place where the mass extinction of megafauna did not happen was Africa, where humans had long lived side by side with large mammals.

A painting of early casualties of the Sixth Extinction: woolly mammoths, woolly rhinos, horses and cave lions during the Ice Age
This image depicts a European landscape during the last Ice Age. Various prehistoric megafauna can be seen, including woolly mammoths, woolly rhinos and cave lions.
Image Source: Caitlin Sedwick

As the centuries progressed and humankind reached every corner of the globe, the problem only intensified. During the past 500 years, over 875 known species of animal have gone extinct – including those ‘A-listers’ of annihilation: the dodo (pictured at the top of this article), passenger pigeon, quagga, great auk and elephant bird – and there are probably countless more that died out even before they could be formally discovered.

Unlike previous extinction events, which were the result of natural climatic shifts, geological activity or even cosmological events, responsibility for the current losses is almost entirely down to us. To provide for our ever-increasing numbers, we have felled forests and drained swamps. In order to build our homes, we have covered vast areas of fertile, ecologically rich land with concrete. The seas are warming as a consequence of the climatic changes we have caused, and they are seriously polluted by poisonous waste and plastic that we have so thoughtlessly thrown into them.

Two vaquita in the ocean
The vaquita is the most endangered marine mammal in the world and a victim of our modern lifestyle. They are often accidentally caught in commercial fishing nets and drown. Fewer than 20 wild individuals are thought to remain in the wild, with none in captivity.
Image Source: Paula Olson

Today’s animals are undoubtedly facing unprecedented challenges. Over the past few centuries, wild animals that were once abundant have been decimated and now survive in dangerously small numbers. The Millennium Ecosystem Assessment estimates that, on average, 24 species of organism, many of which are unknown and undocumented, go extinct every day. Others think that the figure should be much higher – as many as 150–200 a day. This means that the modern rate of extinction is thought to be between 100 and 1,000 times the natural background extinction rate – with no sign of slowing down.

Thankfully, critically endangered species can be saved from total oblivion thanks to intensive conservation efforts. We have proved this many times over the past one hundred years or so. From fewer than 2,000 sea otters at the turn of the 20th century, there are now well over 100,000 frolicking in the coastal waters of the Pacific Ocean. The population of the white rhino, meanwhile, has rebounded from fewer than 100 individuals in the early 1900s to over 20,000 today.

The echo parakeet was almost a casualty of the sixth extinction, but conservation efforts managed to save it
The echo parakeet from the island of Mauritius was once considered the rarest parrot in the world, with fewer than 12 individuals remaining in the 1980s. Now, thanks to conservation efforts and captive breeding, there are more than 750 echo parakeets in the wild and the species is no longer considered endangered.
Image Source: Colin Houston

But before we congratulate ourselves on a job well done, it should be noted that conservation successes are significantly outnumbered by bad news. Time and time again, we fail to take action and simply stand by and watch as endangered animals slide towards extinction, only springing into action when their situation becomes so desperate that they are teetering on the point of no return.

The 20th century was a disaster for nature. And I have to say that, so far at least, the 21st century hasn’t been much better. One study estimates that populations of backboned animals have declined by an average of 60% since 1970. But now science is focusing not so much on saving each endangered species within its own isolated bubble, but on conserving entire habitats and ecosystems. Upsetting the balance of those finely-woven, self-regulating ecosystems can lead to grave consequences. Humans need to realise and accept that we are part of that complex interconnected web of life, not simply a dominant species that can do with the planet whatever we want.

‘It’s never been more important for us to understand the effects of biodiversity loss, of how it is that we ourselves are responsible for it. Only if we do that, will we have any hope of averting disaster.’

Sir David Attenborough

The majority of species that exist today are in peril. Will the modern era be a dystopian age of disaster and more mass extinctions? Or will humans rise to the challenge of managing our planet and taking care of its inhabitants? Can we end our dependence on fields such as coal and oil and find ways of providing our needs more cleanly and efficiently? Can we back and elect leaders that accept responsibility for the many global changes that are required? Can we transform the way we live, the way we consume resources, and the way we eat fast enough to preserve and restore nature? If so, we may reduce further casualties of the Sixth Extinction to a minimum and build a healthy, thriving world for ourselves and future generations.


  • Jason Woodcock

    With a background in conservation and animal behaviour studies, Jason's passion lies in the natural world. He adores all things nature and enjoys nothing more than spotting rare and interesting species out in the wild. He has also worked in a zoo and knows plenty about keeping the animals inside our homes healthy and happy, too.

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