Rereading Darwin: Science now takes for granted the importance of forces and time spans we can’t perceive directly
Two centuries before Charles Darwin wrote On the Origin of Species, Bishop James Ussher calculated the age of the Earth. To do so, the Primate of All Ireland (time has given his title a certain irony) carefully mined the Old and New Testaments for genealogical information that might lead him back to the date of Creation. In so doing, he concluded that the Earth was only about 5,600 years old. It’s easy to ridicule the bishop and his date, but to do so misses a larger point. Ussher’s approach was rigorous—even elegant—and he seemed to understand that the Earth’s age could only be inferred through careful observation of evidence. What doomed his result—and, indeed, many a conclusion in science—were faulty assumptions. The bishop, who took as an axiom that the biblical account of Creation was literal, painstakingly did the math attendant on the notorious biblical begats. He then dutifully added to his tally the five days that separated the creation of the Earth from the creation of human beings, and arrived at the exact date of Creation: October 23, 4004 B.C. Of course, he was wrong.
A Subtle Blow
By the 18th century, scientists in various disciplines had used diverse approaches to calculate the planet’s age and reached different conclusions. As they did, the Earth got older. Still, by the mid-19th century, when Darwin was writing the Origin, the age of the planet was a contentious issue. Although the 4004 B.C. date had fallen from favor, estimates still varied wildly and tended to err on the side of youth.
What Darwin realized was that a youthful Earth was appealing not only because it adhered to the biblical time line, but also because it was simply easier to imagine. He knew that his own argument for natural selection depended on vast conceptions of time, and he also understood that the time spans required would be nearly impossible to comprehend. In a section of the Origin entitled “On the Lapse of Time,” he wrote:
It is hardly possible for me even to recall to the reader, who may not be a practical geologist, the facts leading the mind feebly to comprehend the lapse of time. He who can read Sir Charles Lyell’s grand work on the Principles of Geology … yet does not admit how incomprehensibly vast have been the past periods of time, may at once close this volume.Darwin feared that his readers would be unable to understand the deep time over which natural selection acts, and that their failure would be problematic for his argument. Those with limited imaginations might as well put away his book at once.