Is there divine justice in AIDS? Why now, and not before?

Retroviruses emerged before Homo sapiens in the course of vertebrate evolution. The first human retrovirus was isolated in 1979; the human immunodeficiency virus (HIV-1) assumed epidemic importance in 1981. That such a novel threat to the survival of our species struck only when we had in place, for the first time, the science necessary to fight back seems remarkably coincidental. Cause-and-effect explanations include (1) human activities unique to the late 20th century and (2) a merciful, slow-to-anger God willing to "hold back" until the right time (chairos). By either possibility, AIDS might signify our failure to manage properly the world's ecosystems, the limitations of scientific progress, and/or deficiencies in our collective worldview.