【正文】 tinction of life forms on this pla, rivaling the previous five known prehistoric mass extinctions of life in prehistoric times. Eldredge adds: Everything is linked?. The world truly is a plex system, and we are a part of it, still dependent on its renewable productivity, which we ourselves are beginning to stifle. Appreciating the Benefits of Plant Biodiversity, by John Tuxill, published in 1999 by the Worldwatch Institute, deals with plant extinction. Tuxill39。t need prairie at all. We see prairie as simply underutilized terrain. We even tend to look at marshes like the Hackensack meadowlands and see instead Giants Stadium and the potential for still more entertainment and business plexes rather than a New Jersey tidal wetland full of cattails, migrating birds, and larval marine life vital to the restocking of the marine fisheries on which we still so heavily depend. The Botswanan cattle industry looks at the grasslands of the Kalahari and increasingly, the greener pastures of the Okavango Delta itself as underutilized rangeland. We have e by this outlook honestly: Having stepped outside local ecosystems so successfully, starting 10,000 years ago, we have e to think that we no longer need prairies, wetlands, or any other kind of natural habitat. Agriculture has been a stunningly successful ecological strategy. Though famine has stalked the enterprise from its inception (there really is no such thing as plete control over food supplies, or anything else for that matter), the best indicator of ecological success is growth in population numbers. Estimates vary, but it seems likely that there were no more than 5 million humans on the pla 10,000 years ago. We had recently pleted our spread throughout the globe by then, but we were still anized into relatively small groups as huntergatherers, still utterly dependent on the productivity of the local ecosystems in which we all continued to live. The upper limit on human population numbers back then was set by the same rules that govern the numbers of all other species: Each population is limited by the environmental carrying capacity, the number of individuals that, on average, a local habitat can support, taking into account available food and nutrient resources, and other important factors, such as prevalence of predators and diseasecausing microbes, and even more general factors, such as climate and rainfall. Each local population is fixed at some fluctuating number, usually 30 or 40 individuals maximum, as was usually the case with San and other huntergathering human beings. Thus, the total number of individuals of any species is the average size of its local populations multiplied by the number of those existing populations. Agriculture popped the lid off natural regulation of human population size. No longer limited by the inherent productivity of local ecosystems, human agricultural societies began to expand immediately. Agriculture enables a settled existence and as populations began to grow, as patterns of political control and the division of labor began to emerge, human life rather quickly took on a semblance basically familiar to those of us living in even the most advanced of modern societies. Nor is this, of course, a bad thing: All of the great acplishments of human civilization spring from our forsaking the local ecosystem and adopting agriculture as perhaps the pinnacle of our culturedominated mode of making a living in the world. If high culture is one signal of our success, so too, in the timehonored measure of ecological success, is our geometric increase in the number of individual living humans at any given moment. If there were perhaps as many as 5 million people alive 10,000 years ago, there are now nearly 6 billion [thousand million] of us. We are engaged in a perpetual race to feed ourselves, and every time we e up with a clever expansion of agricultural technology whether it be crop rotation and efficient plowing techniques a few centuries ago, or biotechnological manipulation of the geics of crop plants today human population numbers expand right along, so that there are always people on the brink of starvation somewhere. The sheer bulk of human numbers this 6 billion and everexpanding, probably nearly doubling to over 10 billion by mid21st century is wreaking havoc on Earth, on its species, ecosystems, soils, waters, and atmosphere. We are the current cause of this great environmental crisis, this threat to the global system that looms even as we approach the Second Millennium. We have created the biodiversity crisis, the next great wave of mass extinction that promises to rival the five greatest extinctions of the geologic past The Sixth Extinction?. THE VALUES OF BIODIVERSITY Three themes crop up in everybody39。 (2) ecosystem services (vital functions such as the continued production of atmospheric oxygen)。t know how our telephones, TV sets and puters work, we really have only the vaguest idea of where our foods and medicines e from. Harder yet to understand is the significance for our very existence of species and ecosystems which seem to just sit there and provide no obvious product for us to eat, use as fuel, or stock our medicine chests. Vaguer still is the calm sense of joy and simple belonging most urbanites experience with a simple walk in a woodlot, through a meadow, or along a clean shoreline. Yet these three categories of the effects of the living world on human life are absolutely crucial to modern and future human life on pla Earth. UTILITARIAN VALUES OF BIODIVERSITY When asked how many species humans routinely utilize in their daily life, most people (including most professional biologists) say, at most, perhaps one or two hundred. The correct answer is at least 40,000: Globally, each day we depend on over 40,000 species