PRIOR to the current wave of extinctions that is engulfing our planet, the living world has seen five mass extinctions. Despite the precarious imbalance that resulted, life on earth recovered and got back to previous levels of biodiversity, albeit slowly. In some ways this was good for us humans. For example, I'm just as glad that I don't have to run from a hungry Tyrannosaurus rex, although the image provides fodder for exciting cartoons and movies. Moreover, humans almost certainly would not have evolved had the demise of most dinosaurs not left the world open for the small mammals that eventually gave rise to our own ancestors.1 Life on earth would be very different today, and we would not be here to take the blame for the demise of so many species.
Mass extinctions of the past bring up some vexing questions. Since they have happened before, are they not part of the natural order of this planet? After all, I've emphasized that the extinction of species and the generation of new ones is as normal as the life and death of individuals. Something is always left behind that seeds the next evolutionary era. Won't life recover its diversity through the evolutionary process even though it is temporarily depauperate of biodiversity? Aside from the discomfort of not knowing what position (if any) that humans would hold in a new world order, it seems reassuring that we cannot easily kill off a whole planet no matter how many of us there are.
Whereas hordes of early human hunters decimated the North American fauna thousands of years ago, both the Native Americans and the later European explorers found a rich land teeming with life. Today we still talk about the value of "pristine" wilderness, although no lands are truly beyond human impact. Such places just seem that way because they hold diverse species in a smoothly functioning ecosystem. So maybe our impact hasn't been that bad, and we can afford to lose a few more species here and there. The loss of species may sadden the bunny huggers, but the earth's ecosystems will march into a new era and take us along for the ride. Or will they?
In the opening chapter I made the following claim: conserving biodiversity is vital to the health of our planet, and consequently is vital to us. Throughout other chapters I have touched on the evidence and reasons behind this bold statement. Now it is time to pull the evidence together to show that there are practical reasons for conservation, and to demonstrate that our pension plan for nature must include a diverse portfolio. Of Charles Elton's reasons for conservation — religious, aesthetic and intellectual, and practical — only the practical reasons go beyond bunny hugging to logic necessary to convince an overpopulated world of people to slow down their reproductive habits.
We need biodiversity for a sustainable planet that includes human beings. Biodiversity is necessary at all levels — ecosystem, species, genetic, and everything in between. Without it we too can get dragged into extinction like the mighty Tyrannosaurus rex. But that is no way to solve our overpopulation problem. If I am sounding "alarmist," it is only because there is genuine cause for serious alarm. So let's look at the value of biodiversity at different levels. There is no time to lose.
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