Humans will be fine---Adaptation and immune systems check

The end of humanity is far more likely to be brought about by multiple factors, Kemp says—a pileup of disasters. Although apocalyptic movies often turn to viruses, bacteria and fungi to wipe out huge swathes of the population, a pandemic alone probably won't drive humanity to extinction simply because the immune system is a broad and effective defense, says Amesh Adalja, an infectious disease physician and senior scholar at the Johns Hopkins Center for Health Security. A pandemic could be devastating and lead to severe upheaval—the Black Death killed 30 to 50 percent of Europe's population—but it's unlikely that a pathogen would kill all of humanity, Adalja says. "Yes, an infectious disease could kill a lot of people," he says, "but then you're going to have a group [of people] that are resilient to it and survive."

Humans also have tools to fight back against a pathogen, from medical treatments to vaccines to the social-distancing measures that became familiar worldwide during the COVID pandemic, Adalja says. There is one example of a mammalian species that may have been entirely eliminated by an infectious disease, he says: the Christmas Island rat (Rattus macleari), also called Maclear's rat, an endemic island species that may have gone extinct because of the introduction of a parasite.