A common misconception is that evolution relies entirely on chance. For example, I once read part of a science textbook intended for homeschooling parents that included this analogy:
Imagine a yard containing all of the parts of a working computer that has been disassembled and the parts have been strewn all over the yard. How likely does it seem that a tornado could blow through the yard and randomly reassemble the parts to once again form a working computer?
This is an attempt to update the old Boeing 747 analogy from Fred Hoyle. He was attempting to illustrate the improbability of certain elements of life originating by chance.
Since such abuses of probability estimation seem to thrive still today, particularly in forums that are dominated by amateur commentators (I’m talking about you, Facebook), I thought it might be worthwhile to discuss a one of the many problems with analogies like this.
The modern theory of evolution—or you may hear it referred to as the modern synthesis—does not suggest that evolutionary events are the products of mere chance. While chance is a factor, such as in random mutations, it is not the only one. Consider 10 types of birds living on an island with 10 different beak shapes. Let’s suppose the available food source for these birds is only reachable by one of the beak shapes (perhaps it’s in a narrow hole or something). A naïve treatment of the probability of survival here would assign equal weight to every type of bird. However, we should easily recognize that survival is not random here. It will specifically favor the bird type that is able to reach the food source. So, there is a non-random factor at work. Specifically, reaching the food is needed for reproduction and survival and not all bird types can reach the food. An entirely natural process is performing selection.
Let’s also look at an example that does not involve living things. If you’re on a rocky beach, you might notice the distribution of rocks and pebbles has a specific pattern. Rocks will be sorted according to their size. There will be fairly uniform layers running parallel to the water. Let’s approach the problem like a creationist and see how we incorrectly determine the probability by thinking it’s random. To keep it simple, we’ll assume a small sample space of 16 rocks. Each letter group means the rocks are roughly the same size.
If I were to randomly pull rocks out of a bag and place them into the 16 squares, I calculate the chance as only 0.0000000159 that this pattern would appear. This is being pretty generous in that we have only 16 squares to fill and any of the A rocks can be in the first row, B rocks in the second row, etc. Even given these concessions, random chance is an unlikely explanation. So, should we conclude that there must have been intelligent involvement? Of course not. We know there are natural processes selecting for rock placement just as natural processes select for survival.
Any argument that calculates a probability based on random chance alone ignores this known feature, thus, is arguing against a straw man.
[Cross-posted at An American Atheist]