'There are 4,640 species of mammals, all of whom breastfeed their young. Lactose is present in most of the breastmilk of these species. Humans are but one species of mammals, but are the only species with any significant decay in deciduous teeth. Mammals, starting with the Australopithecines have been on the earth for 2 to 4 million years.19 Modern Homo sapiens have been around for 30,000 to 35,000 years. Dental decay, however, did not become a significant problem until about 8,000 to 10,000 years ago. Anthropologists believe the increase in decay was primarily due to the advent of the cultivated crops. Some anthropologists believe it would be evolutionary suicide for breastmilk to cause decay and that evolution would have selected against it.'
(from the link you posted spiderlight- but so obvious, I felt it needed highlighting!)