evidence: As SARS-CoV-2, the coronavirus that causes COVID-19, has spread throughout the world, many observers have failed to take note of the millions of illnesses and deaths caused by HIV—another virus that has approached pandemicstatus during its history. Now an HIV variant that is more virulent and transmissible has been discovered in the Netherlands, where it apparently has been circulating for decades, according to new research. Luckily, none of the variant’s new mutations make it resistant to widely used therapies. But the finding may offer a warning for how the COVID pandemic could proceed in the coming months: viruses do not necessarily evolve to become milder. [...] William A. Haseltine, an infectious disease researcher who founded Harvard University’s cancer and HIV/AIDS research departments and now chairs the think tank ACCESS Health International, has written extensively about the potential of SARS-CoV-2 assume a more dangerous form. Haseltine spoke with Scientific American about why a more virulent variant of HIV—a virus that has been known for nearly half a century—is just coming into focus now, whereas the new coronavirus has spawned several "variants of concern" in a matter of months.