I was wondering if researchers have given any thought to the idea that in the same way that disease devastated human populations after the European discovery of the Americas, perhaps disease was a contributing factor in the demise of much of the fauna of the Western Hemisphere. Could domesticated animals traveling with the humans, or maybe wild animals making use of the same pathways, have carried pathogens so alien to the native populations that they perished?

Bob Stewart
Florence, Mass

Couldn’t most of the life-threatening damage have been caused by excessive radiation? That is, larger animals would have taken bigger doses—especially with forests dwindling—while smaller animals could more easily have found shelter. Meanwhile, seagoing creatures had the advantage of a water shield.

Buz Craft
Wills Point, Texas

A hypervirulent disease, climate change, and rapacious hunting by humans newly arrived in the Western Hemisphere—alone or in combination—are often blamed for the megafauna die-offs at the end of the last ice age (SN: 12/4/99, p. 360: https://www.sciencenews.org/pages/sn_arc99/12_4_99/bob1.htm). Either wild or domestic animals could have been the source of disease, if it played a role. On the idea of excessive radiation as extinction culprit: The scenario doesn’t explain why similar extinctions weren’t happening simultaneously on nearby continental landmasses .—S. Perkins