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Understanding Bayesian Analysis, the Evolution Skeptic’s Friend

Stephen A. Batzer

man jumping off bridge.jpg

If you’ve followed the ID vs. Darwinism debate at all, you’ve probably come across the term “Bayesian analysis.” This technique is the skeptic’s friend and it can actually be very simple if informally used. Englishman Thomas Bayes was an 18th-Century Presbyterian minister and mathematician. He asserted that it is rational to analyze new data based upon prior knowledge.
This is subjective probability analysis, the opposite of data analysis “in a vacuum.” Here’s a handy example. Many of us recall being asked by our parents, “If everyone were jumping off a bridge, would you do that too?” I don’t think my mother asked me again after I told her, “Almost certainly. There must be a solid reason that everyone is jumping off the bridge. You probably would, too.”
This down-and-dirty analysis isn’t absolutely reliable, but it is cogent and we all use it every day. People commonly make choices in what they believe and do for experiential reasons. Here’s another example; a bad choice is superior to an intolerable choice. In 2001, intelligent, well-educated adults jumped out of skyscrapers to certain death. Why would did they do such a thing? Because jumping was better than burning to death. When they jumped, fuel-fed flames were working inexorably up through the World Trade Center.
Imagine you were in the vicinity on that infamous day. When you witnessed the first plane impact at 8:46 a.m. into the north tower, you would likely think that this event was an accident. Who would deliberately commit such barbarism? But at 9:03 a.m., when the second plane crashed into the south tower, your analysis would instantly change. No intelligent person would then think that the second impact was just another accident, totally independent of the first. Both conclusions are based on forms of Bayesian analysis.
After the first crash, your experience informed you that what you witnessed was likely a tragic accident. Kamikaze attacks hadn’t occurred since 1945; they were in the Pacific, not New York; the United States was at war then, which it was not in 2001. However, the second impact occurred mere minutes after the first, striking the same building complex. The probability that these events were independent was vanishingly small. Even before Al Qaeda took responsibility, all rational people knew that these acts were not the result of random chance.
Likewise, the majority of Americans are unconvinced that random chance is the causative agent behind life’s development and the increase of biological complexity over time. They remain strikingly immune to the exhortations of any number of intellectuals who regularly call them ignorant, stupid, insane and/or wicked.
Their Bayesian “baloney detector” won’t stop ringing its tinny bell. In The Demon-Haunted World, Carl Sagan wrote,

I meet many people who are offended by evolution, who passionately prefer to be the personal handicraft of God than to arise by blind physical and chemical forces over eons from slime. They also tend to be less than assiduous in exposing themselves to the evidence. Evidence has little to do with it. What they wish to be true, they believe is true. Only 9 percent of Americans accept the central finding of modern biology that human beings (and all the other species) have slowly evolved by natural processes from a succession of more ancient beings with no divine intervention needed along the way.

I think that Dr. Sagan was in error. Was it truly reasonable for him to assert that 91 percent of those people who reject the naturalistic dogma do so solely due to religious belief? Why have 91 percent of the American public left the building? It is their everyday experience that informs them that something is terribly, persistently wrong Darwinism, that the theory simply doesn’t match the evidence.
Jerry Coyne, in his polemic Why Evolution is True, scoffs at those 91 percent who find his analysis unconvincing. He writes, “True, breeders haven’t turned a cat into a dog, and laboratory studies haven’t turned a bacterium into an amoeba … but it is foolish to think that these are serious objections to natural selection.”
Of course these are, in fact, serious objections; Dr. Coyne doesn’t get to choose what data is and isn’t objectionable to others. Major speciation via undirected processes is the crux of the Darwinian narrative. If it can’t be replicated, this objection is an example of what logicians call a “defeater.” If you, an intelligent actor using skill, can’t breed a cat into a different genera, then presumably and reasonably nature can’t do this either.
Further, it is unproductive to address reasoned objections with scorn. Yet Jerry plows onward. “[T]he average rates of evolution seen in colonization studies are large enough to turn a mouse into the size of an elephant in just ten thousand years!” Does any lucid person buy this line of reasoning? It is the persistent presentation of whoppers as unquestionable orthodox doctrine that convinces workaday people that the train of evolutionary thinking has jumped the tracks.
Knowing what we do from the Reverend Bayes, the typical Darwinian objection to ID and theism, that they are “science stoppers,” rings a bit hollow. For further reading, New Yorker business reporter James Surowiecki’s The Wisdom of Crowds gives a highly accessible treatment of this topic. He shows why the masses frequently do better in judging reality than do highly credentialed experts.
Photo credit: Sandor Weisz/Flickr.