" If, on the other hand, people were to blame—and it seems increasingly likely that they were—then the import is almost more disturbing. It would mean that the current extinction event began all the way back in the middle of the last ice age. It would mean that man was a killer—to use the term of art an “overkiller”—pretty much right from the start. "

― Elizabeth Kolbert , The Sixth Extinction: An Unnatural History