It takes a special kind of person to calmly debate those who prefer dogma to reason and who insist on ignoring or distorting evidence to suit their preconceptions. Carl Sagan was such a person. Among his many other scientific accomplishments, he became legendary for his skill as an educator and science advocate. Sagan communicated not only his knowledge, but also his awe and wonder at the beauty and intricacy of the universe, bringing to his explanations an unrivaled enthusiasm, clarity, and talent for poetic expression. And when faced with interlocutors who were less than intellectually honest, Sagan kept his cool and carried on.
This could be difficult. In the audio from a radio call-in show above, we hear Sagan answer questions from a caller with a clear, and rather foolhardy agenda: to best the astronomer, astrophysicist, and astrobiologist in a debate over Darwinian evolution. He begins right away with some ad hominem, calling Sagan and his wife Ann Druyan “true believers, who are no more willing to question the theory that you base your beliefs on than were the ministers of the 19th century who you regularly criticize as being close-minded.” The irony of accusations like these should be obvious. Though the caller doesn’t announce himself as a creationist, it’s abundantly clear to Sagan from his talking points that he’s defending a creationist party line.
Sagan attempts to answer his first question, but before he can finish, the caller leaps to another bullet point, the “gaps in the theory” or “gaping hole” of “fossils in transition.” Sagan presses his claim, with evidence, that “the Darwinian concept of evolution and natural selection is profoundly verified.” The insistent caller again interrupts and Sagan almost gives up on him, saying he “rather reminds me of Pontius Pilate. He asks, ‘what is truth?’ but does not stay for the answer.’” Then Sagan, without hesitation, patiently makes a case in brief:
Consider artificial selection. There is something particularly implausible about natural selection, particularly if you think that the world is only a few thousand years old, as the Biblical chronology would have it. Then the idea of one species flowing into another is absurd, we never see that in our everyday life, we are told. But consider, for example, the variety of dogs on the planet… We humans made them… by controlling which dogs shall mate with which…. In the short period of 8 or 10,000 years, we produce this immense variety of dogs. Now compare that with four billion years of biological evolution, not artificial selection, but natural selection, which goes into not just the overall personality and characteristics of the dog, but the biochemistry and internal organs… and then it is clear that the beauty and diversity of life on earth can emerge. But if you don’t buy four billion years, you don’t buy evolution.
Sagan frequently cited this figure of 4 billion years for the origin of life on Earth. During his hugely popular program Cosmos, for example, he used the number in an accelerated evolutionary history, which you can hear him narrate accompanied by a nifty animation in the video below. Most scientists have used that figure or a few million years earlier. For some time, the actual number was thought to be between 3.6 and 3.8 billion years. Recently, as Tim Marcin reports at the International Business Times, some scientists have concluded that “living organisms may have existed on Earth as long as 4.1 billion years ago.”
Marcin quotes UCLA professor of geochemistry Mark Harrison, who speculates, “life on Earth may have started almost instantaneously” (relatively speaking) after the planet’s formation some 4.6 billion years ago. These estimates come from carbon dating, not fossils, but just yesterday, Sarah Kaplan writes at The Washington Post, discoveries of “tiny, tubular structures uncovered in ancient Canadian rocks” may be evidence of ancient microbes thought to be 3.77 billion years old, “making them the oldest fossils ever found.”
Like all new scientific discoveries, these recent findings have been contested by other scientists in these fields. And like some discoveries, their questions may never be resolved in our lifetimes. Science depends on methods of data collection, evaluation and interpretation of evidence, peer review, and many other processes subject to human error. Scientists must often revise their conclusions and reconsider theories. No scientific explanation is conclusively definitive in all its particulars. Nonetheless, Sagan believed that only through the scientific method could we obtain knowledge about the cosmos and the origin of life on earth that was in any way reliable. He admired religious ethics and the space religions held for the big questions. Sagan even declared in his 1985 Gifford Lectures (published posthumously as The Varieties of Scientific Experience) that “the objectives of religion and science… are identical or very nearly so.” But he did not think religions could answer the questions they asked.