Humans Are Doomed to Go Extinct - Scientific Americanhttps://www.scientificamerican.com/article/humans-are-doomed-to-go-extinct/As a paleontologist, I take the long view. Mammal species tend to come and go rather rapidly, appearing, flourishing and disappearing in a million years or so. The fossil record indicates that Homo sapiens has been around for 315,000 years or so, but for most of that time, the species was rare—so rare, in fact, that it came close to extinction, perhaps more than once. Thus were sown the seeds of humanity’s doom: the current population has grown, very rapidly, from something much smaller. The result is that, as a species, H. sapiens is extraordinarily samey. There is more genetic variation in a few troupes of wild chimpanzees than in the entire human population. Lack of genetic variation is never good for species survival.
What is more, over the past few decades, the quality of human sperm has declined massively, possibly leading to lower birth rates, for reasons nobody is really sure about. Pollution—a by-product of human degradation of the environment—is one possible factor. Another might be stress, which, I suggest, could be triggered by living in close proximity to other people for a long period. For most of human evolution, people rode light on the land, living in scattered bands. The habit of living in cities, practically on top of one another (literally so, in an apartment block) is a very recent habit.
Another reason for the downturn in population growth is economic. Politicians strive for relentless economic growth, but this is not sustainable in a world where resources are finite. H. sapiens already sequesters between 25 and 40 percent of net primary productivity—that is, the organic matter that plants create out of air, water and sunshine. As well as being bad news for the millions of other species on our planet that rely on this matter, such sequestration might be having deleterious effects on human economic prospects. People nowadays have to work harder and longer to maintain the standards of living enjoyed by their parents, if such standards are even obtainable. Indeed, there is growing evidence that economic productivity has stalled or even declined globally in the past 20 years. One result could be that people are putting off having children, perhaps so long that their own fertility starts to decline.
An additional factor in the shrinking rate of population growth is something that can only be regarded as entirely welcome and long overdue: the economic, reproductive and political emancipation of women. It began hardly more than a century ago but has already doubled the workforce and improved the educational attainment, longevity and economic potential of human beings generally. With improved contraception and better health care, women need not bear as many children to ensure that at least some survive the perils of early infancy. But having fewer children, and doing so later, means that populations are likely to shrink.
The most insidious threat to humankind is something called “extinction debt.” There comes a time in the progress of any species, even ones that seem to be thriving, when extinction will be inevitable, no matter what they might do to avert it. The cause of extinction is usually a delayed reaction to habitat loss. The species most at risk are those that dominate particular habitat patches at the expense of others, who tend to migrate elsewhere, and are therefore spread more thinly. Humans occupy more or less the whole planet, and with our sequestration of a large wedge of the productivity of this planetwide habitat patch, we are dominant within it. H. sapiens might therefore already be a dead species walking.
The signs are already there for those willing to see them. When the habitat becomes degraded such that there are fewer resources to go around; when fertility starts to decline; when the birth rate sinks below the death rate; and when genetic resources are limited—the only way is down. The question is “How fast?”