In 1543, a young Flemish anatomist Andreas Vesalius challenged Galen’s theories of the Human Body. This discovery had an impact on scientists. Vesalius’ discovery of the important differences between species also helped usher in the science of comparative anatomy, in which researchers studied animals to find their similarities and differences. In the process, they gradually began to recognize humans as being one species among many, with a few unique traits but many others shared in common with other animals. Some 300 years after Vesalius first shook off the blind obedience to Galen, Darwin used that vast stock of anatomical knowledge to build his theory of evolution.
In 1666, Nicholas Steno dissected a shark; he was struck by how much the shark teeth resembled “tongue stones,” triangular pieces of rock that had been known since ancient times. Steno made the leap and declared that the tongue stones indeed came from the mouths of once-living sharks. He showed how precisely similar the stones and the teeth were. But he still had to account for how they could have turned to stone and become lodged in rock. Steno said that the fossils were snapshots of life at different moments in Earth’s history and that rock layers formed slowly over time. It was these two facts that served as the pillars of paleontology and geology in future centuries. And fossils ultimately became some of the key evidence for how life evolved on Earth over the past four billion years.
In the 1800’s, Theology is the understanding of and providing reasoned discourse of religion, spirituality and the Gods. Natural Theology dominated English thinking for two centuries. Natural theology was important scientifically because it guided researchers to the fundamental question of how life works. Even today, when scientists discover a new kind of organ or protein, they try to figure out its function. William Smith was surprised to find that the fossils in the layers often were arranged in the same distinctive order from the bottom to the top of the rocks. And as he traveled across England, he discovered the same sequences of fossils in rock layers. Each type of animal, he realized, had a widespread existence for a particular span of time, a span that partially overlapped with that of other animals. That made it possible for Smith to recognize the order in which rocks had been formed throughout much of England. In 1831, new generations of geologists appreciated Smith's contribution. This theory impacted geologists everywhere. Geologists used his methods to discover even older geological formations whose outcrops were scattered across England. Meanwhile on the continent, Georges Cuvier and his student Alexandre Brongniart used much the same method to decipher the rocks of the Alps. It became inescapably clear to geologists that Earth and its life were far older than a few thousand years.
"Catastrophism," as this school of thought came to be known, was attacked in 1830 by a British lawyer-turned-geologist named Charles Lyell. For inspiration, Lyell turned to the fifty-year-old ideas of a Scottish farmer named James Hutton. In the 1790s, Hutton had argued that the Earth was transformed not by unimaginable catastrophes but by imperceptibly slow changes, many of which we can see around us today. Rain erodes mountains, while molten rock pushes up to create new ones. The eroded sediments form into layers of rock, which can later be lifted above sea level, tilted by the force of the uprising rock, and eroded away again. These changes are tiny, but with enough time they could produce vast changes. Hutton therefore argued that the Earth was vastly old — a sort of perpetual-motion machine passing through regular cycles of destruction and rebuilding that made the planet suitable for mankind. Lyell had an equally profound effect on our understanding of life's history. He influenced Darwin so deeply that Darwin envisioned evolution as a...