In the essay "Seven Wonders" by Lewis Thomas, what criteria have determined his choices of his seven wonders?

In his essay "Seven Wonders," the distinguished scientist and physician Lewis Thomas responds to the invitation of a magazine to offer his own individual take on the seven wonders of the modern world. Thomas responds to this request by attempting to clarify the meaning of the word "wonder." He observes that the root of the word is Indo-European, and refers to something that makes us smile or laugh. As Thomas points out, "wonder" has connotations of what is marvelous and miraculous; it encourages us to ask questions about the many extraordinary phenomena we witness in the natural world. In the presence of these modern-day wonders, we smile, not just because we find it such a pleasurable experience, but also out of a sense of awe and admiration. Thomas used this definition as his criteria.
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