The Natural History Museum is currently running a rather interesting-looking exhibition. It's called Extinction: Not the End of the World? and according to this review it asks questions that might make the average conservationist squirm: are we merely hastening the demise of already-doomed species, and how have we benefited from previous extinctions?
Some might leap on these questions as an insinuation that we shouldn't be so worried about the human-induced mass extinction that is, according to the data, currently underway with as many as 50,000 species becoming extinct each year. As for the future,
the results reveal 21 percent of all known mammals, 30 percent of all known amphibians, 12 percent of all known birds, and 28 percent of reptiles, 37 percent of freshwater fishes, 70 percent of plants, 35 percent of invertebrates assessed so far are under threat.
It is indisputable that the demise of the dinosaurs 65 million years ago paved the way for the rise of mammals and, eventually, us. And some animals today hardly seem to help their own cause, like the pandas that refuse to have sex or the Kakapo parrots whose defence strategy consists of running up trees, trying to fly (they can't) and promptly flopping back down to earth. Natural selection is one of the key mechanisms of evolution and the doom of many a species. The most successful species are those which can adapt most effectively to their environments. The ones which can't, die out. This seems fair enough. 'Background extinction' - the standard rate of extinction external to catastrophic changes - is calculated to be one species going extinct every 1-10 years. But in the human-ruled Holocene this rate has rocketed.
We are directly and indirectly threatening the existence of countless species through the harvesting of them and the destruction of their habitats. Among the more well-known species we have already lost are the Great Auk, Stellar's Sea Cow, the Baiji White Dolphin, and the Passenger Pigeon. The Passenger Pigeon, hunted to death, serves as a worrying example of the consequences of extinction; it is believed to have had important ecological roles such as the seeding of forest and keeping populations of Lyme disease-carrying ticks in check. So what will the impending removal of so many more species from the biosphere mean for our future?
Nature's extraordinary resilience is born of diversity. Ecosystems are complex webs of interactions between species, with such abundance of different species that usually when one falters another is able to take its place. When an ecosystem undergoes a change, such as the arrival of a non-native species, the more diverse it is the better its chances of adapting are. At a time when other pressures like climate change are already placing ecosystems under severe stress, it seems unthinkable that we still directly and remorselessly drive species towards extinction, or at least to the point at which their numbers become so small that they can no longer carry out their ecological roles. An ecosystem that haemorrhages species will eventually collapse, and so will the lives of any people who depend on it.
But it is more than just that. The oft-used 'tree of life' represents perfectly the evolution and diversity of life on Earth, each branch and offshoot representing a lineage. The human race is close to hacking off many of those branches, destroying all kinds of life forms. No species lasts forever, but many evolve or are survived by genetic relations. We may have lost the mammoths but we still have the elephants, for now. Most if not all cat species, big and small, are threatened; will our housecats be all that remains of the Felidae family one day? It may sound obvious but by destroying species in the present, we also destroy the potential of species that do not yet exist. The reign of humankind requires a redefinition of 'natural selection'.
It can be difficult to extricate the consequences of extinction from the consequences of other environmental damage, but we already have examples of where it has had a calculable effect on humans. Tony Juniper in his book What Has Nature Ever Done For Us? explains how the near-complete loss of several vulture species due to the use of a particular antibiotic in livestock has so far caused the deaths of around 50,000 people. The reasons are that without vultures to compete with, feral dogs gorged on dead livestock and their population exploded, precipitating a huge increase in the number of people dying of rabies; secondly, as the dogs could not clean carcasses as efficiently as the vultures, anthrax proliferated.
A tree cannot survive if you take too many of its branches. You can still call it natural selection if you want. But only so long as you don't mind the same rules applying to the human race. Mass extinction will not be the end of the world, but it may well be the end of our world.