While trying to find a name for these Aruban land snails (possibly Diplopoma crenulatum), I stumbled across a 1971 article by the late Stephen J. Gould, "The Paleontology and Evolution of Cerion II: Age and Fauna of Indian Shell Middens on Curacao and Aruba." Gould makes a number of interesting observations, including the odd fact that snail shells found in the 4000-year-old middens are larger than any alive today. He guesses, logically enough, that past conditions might have been much wetter (and hence more favorable for land snails) on these now dry islands, but also notes that there was no other evidence for this change in climate.
Three decades later, biologist Kees van Nooren has found support for Gould's conjecture. By analyzing pollen and spores from deep sediments, he discovered that desert Aruba was once a lush garden with at least seven different species of ferns, and that the departure of fertile soil coincided with the arrival of European colonists.
I used to imagine that, like most humans, I learned quickly but now recognize that illusion. In those days I would have overlooked these snails and the beauty they are capable of, thanks to persistent (slow) motion and a hard shell.