There is a universally accepted principle of thought which says that given a choice between multiple explanations for a phenomenon the preferred explanation is the one which is simplest and fits all the facts.
Mathematician Granville Sewell at Evolution News and Views invites us to imagine a scenario which illustrates this principle:
A high school science teacher rents a video showing a tornado sweeping through a town, turning houses and cars into rubble. When she attempts to show it to her students, she accidentally runs the video backward .... [T]he students laugh and say, the video is going backwards! The teacher doesn’t want to admit her mistake, so she says: “No, the video is not really going backward. It only looks like it is .... and she proceeds to give some long, detailed, hastily improvised scientific theories on how tornadoes, under the right conditions, really can construct houses and cars.That's the simplest explanation for the phenomena in the video, certainly simpler than the teacher's contrived explanation, and thus it should be preferred.
At the end of the explanation, one student says, “I don’t want to argue with scientists, but wouldn’t it be a lot easier to explain if you ran the video the other way?”
Sewell wants to relate this to the problem of undirected Darwinian evolution.
Imagine, he writes, a professor describing the final project for students in his evolutionary biology class. “Here are two pictures,” he says. “One is a drawing of what the Earth must have looked like soon after it formed. The other is a picture of New York City today, with tall buildings full of intelligent humans, computers, TV sets and telephones, with libraries full of science texts and novels, and jet airplanes flying overhead.That's the problem with Darwinian evolution. The idea that blind chance and the laws of chemistry alone could have conspired to create a living cell, or produce a process as extraordinary as butterfly metamorphosis, or create a structure as unimaginably complex as a human brain requires so many assumptions and ad hoc explanations, so much suspension of incredulity, that it's far simpler, and much more in keeping with our everyday experience, to posit that these things were the intentional product of an intelligent mind.
Your assignment is to explain how we got from picture one to picture two .... You should explain that 3 or 4 billion years ago a collection of atoms was formed by pure chance with the ability to duplicate itself, and these complex collections of atoms were also able to pass their complex structures on to their descendants generation after generation, even correcting errors that crept in.
Explain how, over a very long time, the accumulation of genetic accidents resulted in greater and greater information content in the DNA of these more and more complicated collections of atoms, and how eventually something called “intelligence” allowed some of these collections of atoms to design buildings and computers and TV sets, and write encyclopedias and science texts....
When one student turns in his essay some days later, he has written, “A few years after picture one was taken, the sun exploded into a supernova, all humans and other animals died, their bodies decayed, and their cells decomposed into simple organic and inorganic compounds. Most of the buildings collapsed immediately into rubble, those that didn’t, crumbled eventually. Most of the computers and TV sets inside were smashed into scrap metal, even those that weren’t, gradually turned into piles of rust, most of the books in the libraries burned up, the rest rotted over time, and you can see see the result in picture two.”
The professor says, “You have reversed the pictures! You did it backwards” “I know,” says the student, “but it was so much easier to explain that way.”
Otherwise, Sewell concludes, the process is like a movie running backward. The whole of biological history is as improbable as assuming that purposeless, undirected forces like tornadoes could actually cause scattered debris to assemble into complex, well-integrated structures.
Of course, if a mind was somehow directing the process that would change everything.