Back in 1985 E. O. Wilson wrote about1 the huge number of species that had so far been discovered and mused about the potential for the discovery of even more. He understood that we had no basis for assuming we knew all of the species on the plant, but he was not just concerned about numbers. He knew that plants and animals had value for the human race, either as direct sources of chemicals or material (drugs, food, fibre), or as parts of support chains for other plants or animals. He wanted both of these aspects studied in more detail so that we actually got somewhere towards understanding the ways in which our surroundings worked, with the intention of avoiding possible loss of things we currently use, and enabling possible discovery of more that we might benefit from. In economic terms Wilson was sure that there was an opportunity cost associated with loss of biodiversity; a cost that would easily be avoided by, as he put it, an investment in study "...which would approximately equal the lifetime cost of one F15 Eagle fighter bomber."
Concern over biodiversity, then, is not just about hand-waving and demanding that we, humans, leave well alone. That is important, of course. In part, it seems morally right to recognise that the world as we see it has been developing over millions of years and it is wrong of us to destroy it. If we look more closely, we can see that the plants clean and purify the air we breath and the water we drink, and this in itself might be enough to give us pause. But looking more closely still we see that much of our food still depends on the outside world. We rely on wild pollinators for nut and fruit crops. We rely on fungi, microbes and small invertebrates to maintain soil condition and to help our crops take up the nutrients they need. We rely on some wild plants for essential medicines. And it doesn't work to consider each of these problems in isolation. The world is so interconnected that the loss of one thing can lead to the loss of another and, in so many cases, we don't know what those interconnections are, or how wide their impact, until they fail.
We know that we are loosing species and ecosystems. Climate disruption is making things too hot for people, animals and plants. CO2 pollution is both heating and acidifying the oceans, killing off coral and plankton and devastating populations of fish and sea birds. Agriculture's extractive mining of top-soils and forests is is eating in to habitats and threatening species from micro organisms to large mammals. And, in general, extractive mining across the world is causing damage wherever it goes. We know that this loss is reducing the Earth's ability to handle pollution. We know that we are threatening our own existence.