No, this isn’t one of Ant and Dec’s new reality TV shows, you and I are genuinely involved. In the history of the world so far there have been 5 mass extinctions that we know of. These are events that, for various reasons, cause a huge drop in species diversity, which can be identified in the fossil record. One of the most famous mass extinctions was that which wiped out the dinosaurs; at least 50% of plant and animal species went extinct, and that was the most recent of the ‘big five’… or was it? Scientists are claiming it’s happening again. We are currently IN one of these extinction events and this time there’s no meteor involved – the cause is humans.
This 6th mass extinction is being termed the ‘Holocene extinction’ and is estimated to have started about 11500 years ago – not exactly an overnight loss but in evolutionary time it’s the blink of an eye. At this time the last ice age was ending, so the withdrawal of ice and change in climate was too much for some species. The retreat of the ice sheet, however, was followed by the spread of humans, as it was not long after that Neolithic people began to settle and farm, rather than being nomadic hunter-gatherers. This lead to the domestication of crops and animals, which may have caused extinction of wild species over time and the spread of disease between humans and animals, which increased as people began to travel greater distances.
Some of the first recognised extinctions were that of the worldwide megafauna – a range of mammals much larger than most found today. Animals such as elephants and rhinos are a mere fraction of the size of the giants that once roamed the earth. Giant sloths that were too big to climb trees used to roam the Americas, whilst woolly mammoths stomped around Eurasia. There were lions in North America that were more than a quarter bigger than those found in Africa today. The retreat of ice-age glaciers was initially blamed for a lot of these extinctions, but hunting is also thought to have contributed. Due to the fact that these animals had small litters every few years, they would have been incapable of sustaining a small or intensively hunted population, as those killed would not be replaced.
As we move closer to the present day, the industrial revolution has left a huge scar on the health of our earth. Factories, machinery and the increased use of fossil fuels have released pollutants and greenhouse gases, which are warming our climate. Humans are also changing land-use all over the world: clearing forests to make way for agricultural land and expanding villages and towns into the countryside. This has already affected particularly delicate ecosystems, for example the golden toad in Costa Rica went extinct around 1989 due to drying of its habitat and invasive species brought in by humans. All it takes is a Google search to show some of the fascinating species we have already lost, such as the thylacine and the quagga.
It is predicted that we are currently experiencing extinctions at 1000 to 10000 times greater than the ‘normal’ background rate. Whilst debate remains as to whether this is due to humans or not, we can certainly blame ourselves for part of it. For example, the western black rhinoceros was declared extinct in November, hunted into non-existence. There are many more extinctions humans can’t record because the species haven’t been identified yet. It is estimated that we are only aware of less than 20% species on this planet, so scientists must race against time to document more before they die out.
For thousands of years nature has been admired and even worshipped, but it is only recently that humans have become aware of the damage we are doing to our earth. There are some species that we will never get back, and some that we have no hope of helping to recover. Whether humans or the climate is to blame, there are future sources of medicine out there and undiscovered crops that will survive global warming, that we must find and preserve.