Extinction
Arthur ’18 [Wallace; November 5; Emeritus Professor of Zoology at the National University of Ireland, evolutionary biologist and science writer; Harvard University Press, “20. Extinction and How to Avoid It,” p. 237-248]
The first of these causes is disease, and specifically those diseases that are caused by microbes—loosely defined to include both bacteria and viruses. Inherited diseases can have appalling consequences for individuals, but they’re not a threat to our species. Diseases caused by animals, such as schistosomiasis, the disease agent here being a parasitic worm, can also have very adverse effects on the people suffering from them, but they are unlikely to cause human extinction. In contrast, diseases caused by microbes are a potential threat to the continued survival of humans on planet Earth.
The reasons for this assertion are as follows. The shorter the life cycle of an organism, the faster it can evolve. And when a disease agent has a very short life cycle and its host a very long one, the discrepancy between the two is most likely to result in an evolutionary advantage to the former. Also, the changing fates of host species in terms of their population numbers will be a major factor driving the evolution of the disease agent. Once upon a time, a few million years ago, the population numbers of protochimpanzees and protohumans were probably about equal. Now there are less than half a million chimps and more than 7 billion humans—so there are about 10,000 humans for every one chimp. If you were a bacterium currently specializing in chimps, what evolutionary trajectory would you choose?
When antibiotics were discovered, in the early twentieth century, they were a boon to medical science. They cured many bacterial diseases. And to some extent they still do. But, given the ability of bacteria to evolve very rapidly, we now live in the age of so-called superbugs, such as MRSA (a label for tough strains of the Staphylococcus aureus bacterium), which are resistant not just to one antibiotic but to lots of them. The superbacteria of the future will be even more problematic, and may constitute an extinction threat. What tactics should we take in order to avoid this fate? The short answer is to dramatically increase the funding for biomedical research.
Superbacteria are a real threat, but the threat posed by viruses is even greater. Contrary to what some people think, most disease viruses are unaffected, or only negligibly affected, by antibiotics. If you have influenza, which is caused by a virus, and you take antibiotics, you won’t be cured by them (though you probably will be helping bacteria to evolve antibiotic resistance). Viruses are harder to deal with than bacteria; vaccines work well in some cases, but in other cases we’re still struggling to find an effective one.
Think of the serious viral outbreaks that have affected humans over recent times. Some of those that most readily spring to mind are smallpox, Ebola, and AIDS. Smallpox has been eradicated (we think) through effective vaccination campaigns. Ebola, regrettably, has not; at the time of writing there is no effective vaccine, but there is much ongoing research to try to find one.
AIDS is worthy of particular attention because of the part of the body that the virus concerned attacks, and because future versions of this type of virus may pose an even greater threat to humanity than the current versions. All disease viruses target some parts of the body more than others. But in the case of the human immuno- deficiency virus (HIV), which causes AIDS, it primarily targets cells of the immune system— the very system whose job it is to protect us from infections.
This is a bit like an enemy state having developed a weapon that only affects our military personnel: something that causes soldiers to die so that our enemy can invade our country and enslave our civilian population. The parallel isn’t perfect, because a civilian can become a soldier, whereas a brain cell cannot become a white blood cell of the immune system. Nevertheless, the analogy helps to illustrate the dangers to an organism of hostile agents specifically targeted at that entity’s defense system. As with Ebola, there are no effective AIDS vaccines as yet. There are some treatments that are partially effective, such as the drug AZT; also, combinations of drugs can be more effective than single ones. But not only are these drugs inadequate right now, they may become even less adequate in the future. Just as with bacteria evolving resistance to antibiotics, viruses can evolve resistance to the various agents used against them.