Eventually the human race will become extinct, like any other species. Ultimately, we should be concerned with what we can do toward our species goals within the one-to-two million-years lifespan of our species. Our individual life spans are not meaningless even though we know they will end. Therefore, what we do as a species is not meaningless just because our species will come to an end.
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It may sound strange to consider extinction as a solution to the problem of the relation of human beings to the rest of nature. But if the human race were to go extinct, that would mean that the problem of its conflict with nature would no longer exist. In any case, since no species lasts forever, extinction is something the human species will someday have to face. We can distinguish two kinds of extinction: Gradual extinction and sudden extinction. Species of living things on this planet have an average life span of two million years. So gradual extinction would be analogous to individual death from old age. The species would simply have run its course in nature, its numbers would diminish, and finally there would be no more human beings, members of the species Homo sapiens. Within this scenario, there are two other possibilities: Either there are similar but better adapted species which supersede Homo sapiens; or the ecological niche Homo sapiens occupies is itself no longer available.1
The existence of similar but better adapted species—namely us—is exactly what caused the extinction of our predecessor species Homo erectus, Homo sapiens neanderthalensis, and perhaps others.2 The existence of more advanced species among us has been a theme of some science fiction stories. The recent X-men films and stories are an example. It is difficult, however, to see how a separate population of genetically different humans could maintain themselves in the current state of human civilization. With physical communication worldwide, any mutation would be fairly quickly incorporated into our worldwide gene pool. Evolutionary biology tells us that the appearance of a new species superseding an older one requires the physical separation of part of the older species population. This process, called macroevolution, can produce a new species in the separated population by natural selection or even simple genetic drift.3
The second gradual extinction possibility, the disappearance of our ecological niche, seems most likely as the result of accumulated environmental changes caused by us. For example, a recent dramatic decrease in the fertility of human sperm may have been caused by increased air and water pollution in the environment.4 If this trend gets dramatically worse, one could see the human population diminishing to zero. Of course, one would expect human beings to take steps to reverse this trend well before extinction took place. But there could well be environmental effects on fertility or other critical factors for species survival whose causes elude us long enough to cause extinction.
Nevertheless, the likelihood of sudden extinction is probably greater. There are also two types of sudden extinction: Those caused by natural processes completely external to human beings and those caused by human action. External causes of extinction are collisions with asteroids or comets, or massive volcanic eruptions. Both have caused mass extinctions in the past. An asteroid collision 60 million years ago in the Yucatan most likely caused the extinction of the dinosaurs (Schulte 2010). And 70,000 to 80,000 years ago the supervolcanic eruption at what is now Lake Toba in Sumatra most likely came close to extinguishing Homo sapiens. Some estimate that as few as between 1,000 and 10,000 humans survived (Ambrose 1998). Another example would be the earth’s being an unlucky target of a gamma ray burst (Minard 2009). Such events are not predictable.