Undeniable by Bill Nye

revered were the ancient Greeks that people celebrating the birth of the U.S.’s first president thought it made sense to put an eighteenth-century politician in a minus-fourth-century Greek outfit. As part of that style of thinking, Aristotle’s ideas on the relationships of living things persisted well into the age of Hutton, Lyell, Wallace, and Darwin.
    Back in that fourth century BC, Aristotle postulated that there is a scala naturae , a ladder of nature. In this Latin usage, a ladder is not something you use for climbing. Instead, here, nature’s ladder is how things are arranged or displayed from bottom to top. Nothing on the ladder is climbing or descending; each living thing is placed on each step or rung, like books on shelves. Aristotle observed the extraordinary, even exquisite balance of nature and figured that a creator or natural force set each living thing in its exact place, and there they or we each stayed. Everything fits perfectly, like pieces in a vertical puzzle. Along with this arrangement, though, was the idea that things do change with time. Babies grow up to be cowboys (or discus throwers), for example. They have life cycles, during which they grow and change. But in the bigger picture, they remain in their assigned places. These were parts of the perfect ladder of nature.
    Taking this perfection into account, Hutton wrote repeatedly that, although he could not help but notice that Earth is ever changing, process, too, was part of a creator’s plan. For example: “Nature, everywhere the most amazingly and outstandingly remarkable producer of living bodies, being most carefully arranged according to physical, mechanical, and chemical laws, does not give even the smallest hint of its extraordinary and tireless workings and quite clearly points to its work as being alone worthy of a benign and omnipotent God…”
    The perspective of Hutton and Lyell began to take hold. By the late 1830s, people were actively speculating on the philosophical and scientific consequences of a very, very old Earth. It roughly goes like this: If Earth’s surface has changed slowly over countless millennia, does that mean living things like us have also changed over time? In turn, that might mean that there is no one—to wit, no god—in charge right now. Instead of animals and plants striving for perfection to take their rightful place on nature’s ladder, as ancient philosophers had presumed, we are all just blinks in the slowly moving picture of the long, long stretch of time.
    Like my grandmother’s tenant, many observant people had noted the connections and morphological relationships between different animals and plants. That’s how, in the eighteenth century, the botanist Carl von Linné (Carolus Linnaeus, as it is written in Latinized form) came up with his naming scheme for connecting one type of organism to another. Any living thing could be categorized in a hierarchy each level of which was a binary choice. To place something in a catalog of living things, the naturalist just had to decide, is it animal or plant? Does it have mirror-image symmetrical leaves or long flat leaves? Is it woody or smooth? It’s like a game of Twenty Questions. The Linnaean system further encouraged naturalists to think deeply about the relationships between living things. Linnaeus was so influential that the Linnaean Society is going strong still today.
    By the time Darwin was born in 1809, a number of naturalists were starting to explore how different varieties of living things were related and how they could change over time. Earth seemed old enough to allow such changes to happen, but nobody knew how one species could become another species, no matter how much time was involved. One person came close but got the main idea wrong—you’ll read a whole lot more about him in the next chapter. Then along came Darwin and Wallace and … here we are. Later, people like