We are constantly told by scientists and conservationists how the world's biodiversity is under threat. Animals of all kinds are threatened with extinction.
Well, what if all animals were extinct? What if we really did mess things up so much that we were left on this planet on our own? No animals, no birds, no insects, just humans.
Truth be told we spend much of our lives independent and oblivious to nature, so would it really make a difference? I spoke to a number of experts to try to piece together what life would be like on earth if we were on our own.
Last animal on earth
There was a desperate fight and hundreds of people were injured, but eventually the last animal on earth was killed. A young dairy bull calf, it provided a small meal to just a fraction of the people in its home village in a remote region of Siberia.
That is one fictional ending to animal life on earth. But the reality is that it would not end there. We are so dependent on animals for our own existence that our own end would probably not be too far behind.
"Animals are so integrated into our ecosystem that if they did disappear then we wouldn't have a living planet," says WWF species officer Heather Sohl.
She is not alone in thinking this either. Conservationists have been arguing for years that safeguarding endangered species is far more than a moral obligation. It is a practical one too, given the vital contribution made by animals to the economy and human existence.
The food we eat
As well as providing food through meat and dairy products, animals also play a crucial role in how much of our food grows. Bees, birds and bats all contribute to pollinating a vast range of fruits and wild plants that would otherwise never survive.
"While the direct uses of items like meat, wool and animal by-products such as oil and leather are obvious to most, it's the indirect ones that are really interesting," says Tom Hart, a researcher at the Institute of Zoology.
“Pollination is a free ecosystem service that flowers our plants and is something we just cannot replicate if birds and insects were extinct. That would mean losing most of our cereal crop, flowers and fruits," adds Mr Hart.
Even vegetarians would struggle to survive without cereals and fruits.
But as well as supplying the food we eat animals also protect us. The animal kingdom as it exists at the moment keeps a stable balance on life on earth. If you suddenly take away a predator from a habitat then the next nearest will quickly increase in population and cause chaos. Animals are often the ones keeping the pests at bay.
And it is not just pests they control either but also the landscape.
"Grazing animals keep our grasslands under control and there are many examples where fish are helping to filter inland bays," explains Mr Hart.
Economy and medicine
Animals also provide a livelihood to much of the human population. Although we are over-exploiting many in the case of the illegal trade in ivory or bushmeat, the legitimate fisheries and livestock agriculture sectors are worth billions and provide jobs to millions.
David Jones/PA Wire/PA Photos
And then there is tourism. Developing countries like Kenya would see their tourist sectors collapse if there were no animals to see on safari trips. Likewise, there would be little need for animal parks, snorkelling (no corals or fish) or birdwatching. And what about our pet dogs and cats?
Most importantly of all there is medicine. While animal testing is opposed by many people as immoral, cruel and unnecessary, there is a stronger argument in favour of the many drug products that have been created through animal derivatives.
Life without humans
Although there is a constant concern about protecting endangered animals, extinction is nothing new. There has always been extinction and there always will be, admit conservationists.
So who is to say animals won't be the ones to out-survive us?
“We are far more vulnerable than animals as just one species,” says Jean-Christophe Vie, deputy head of the IUCN Species Programme. “Even with something as severe as a nuclear holocaust - scorpions and rats are known to be far more resistant to radiation than humans,” he adds.
The fact is that animals have managed to live everywhere on the earth, but you won't find many who believe humans will ever be able to survive at the bottom of the ocean or in the deserts of Sahara.
“There is no doubt that nature can survive without humans - and has done so, for the most part, since time began,” says Jean-Christophe Vie.