Viruses Bacteria Protists And Fungi A Really Big Fungus: Fill & Download for Free

Infectious disease is all around us. Infectious disease is a kind of natural mortar binding one creature to another, one species to another, within the elaborate biophysical edifices we call ecosystems. It’s one of the basic processes that ecologists study, including also predation, competition, decomposition, and photosynthesis. Predators are relatively big beasts that eat their prey from outside. Pathogens (disease-causing agents, such as viruses) are relatively small beasts that eat their prey from within. Although infectious disease can seem grisly and dreadful, under ordinary conditions it’s every bit as natural as what lions do to wildebeests and zebras, or what owls do to mice.A person might construe this as a sequence of dire but unrelated events—independent misfortunes that have happened to us, to humans, for one unfathomable reason and another. Seen that way, Covid-19 is an “act of God” in the figurative (or literal) sense, grievous mishaps of a kind with earthquakes and volcanic eruptions and meteor impacts, which can be lamented and ameliorated but not avoided. That’s a passive, almost stoical way of viewing them. It’s also the wrong way.Make no mistake, they are connected, these disease outbreaks coming one after another. And they are not simply happening to us; they represent the unintended results of things we are doing. They reflect the convergence of two forms of crisis on our planet. The first crisis is ecological, the second is medical. As the two intersect, their joint consequences appear as a pattern of weird and terrible new diseases, emerging from unexpected sources and raising deep concern, deep foreboding, among the scientists who study them. How do such diseases leap from nonhuman animals into people, and why do they seem to be leaping more frequently in recent years? To put the matter in its starkest form: Human-caused ecological pressures and disruptions are bringing animal pathogens ever more into contact with human populations, while human technology and behavior are spreading those pathogens ever more widely and quickly. There are three elements to the situation.One: Mankind’s activities are causing the disintegration (a word chosen carefully) of natural ecosystems at a cataclysmic rate. We all know the rough outlines of that problem. By way of logging, road building, slash-and-burn agriculture, hunting and eating of wild animals (when Africans do that we call it “bushmeat” and impute a negative onus, though in America it’s merely “game”), clearing forest to create cattle pasture, mineral extraction, urban settlement, suburban sprawl, chemical pollution, nutrient runoff to the oceans, mining the oceans unsustainably for seafood, climate change, international marketing of the exported goods whose production requires any of the above, and other “civilizing” incursions upon natural landscape—by all such means, we are tearing ecosystems apart. This much isn’t new. Humans have been practicing most of those activities, using simple tools, for a very long time. But now, with 7 billion people alive and modern technology in their hands, the cumulative impacts are becoming critical. Tropical forests aren’t the only jeopardized ecosystems, but they’re the richest and most intricately structured. Within such ecosystems live millions of kinds of creatures, most of them unknown to science, unclassified into a species, or else barely identified and poorly understood.Two: Those millions of unknown creatures include viruses, bacteria, fungi, protists, and other organisms, many of which are parasitic. Students of virology now speak of the “virosphere,” a vast realm of organisms that probably dwarfs every other group. Many viruses, for instance, inhabit the forests of Central Africa, each parasitic upon a kind of bacterium or animal or fungus or protist or plant, all embedded within ecological relationships that limit their abundance and their geographical range. Ebola and Marburg and Lassa and monkeypox and the precursors of the human immunodeficiency viruses represent just a minuscule sample of what’s there, of the myriad other viruses as yet undiscovered, within hosts that in many cases are as yet undiscovered themselves. Viruses can only replicate inside the living cells of some other organism. Commonly they inhabit one kind of animal or plant, with whom their relations are intimate, ancient, and often (but not always) commensal. That is to say, dependent but benign. They don’t live independently. They don’t cause commotion. They might kill some monkeys or birds once in a while, but those carcasses are quickly absorbed by the forest. We humans seldom have occasion to notice.Three: But now the disruption of natural ecosystems seems more and more to be unloosing such microbes into a wider world. When the trees fall and the native animals are slaughtered, the native germs fly like dust from a demolished warehouse. A parasitic microbe, thus jostled, evicted, deprived of its habitual host, has two options—to find a new host, a new kind of host . . . or to go extinct. It’s not that they target us especially. It’s that we are so obtrusively, abundantly available. “If you look at the world from the point of view of a hungry virus,” the historian William H. McNeill has noted, “or even a bacterium—we offer a magnificent feeding ground with all our billions of human bodies, where, in the very recent past, there were only half as many people. In some 25 or 27 years, we have doubled in number. A marvelous target for any organism that can adapt itself to invading us.” Viruses, especially those of a certain sort—those whose genomes consist of RNA rather than DNA, leaving them more prone to mutation—are highly and rapidly adaptive.