When someone at the USGS Earth Resources Observation and Science Center saw this image of the Terkezi Oasis in Chad, taken by the Landsat 7 satellite, he or she saw art and included it in the Earth as Art collection. But when I came upon it, and mentally rotated it by 90 degrees (as shown above), I saw a ghostly screamer with one arm raised in anger.

Admittedly, I had primed my brain for such a discovery, searching for Halloween-ish images in keeping with the season, but I probably would have seen a face even if I hadn’t been thinking of monsters and ghosts. We often find patterns in places where they don’t exist, whether it be a witch’s head in a nebula, initials in the echoes of the Big Bang or the Virgin Mary in a piece of toast.

There are definite advantages in being able to recognize patterns—when they are real, they can provide useful information about the world around us, information that can help us to prosper and stay alive. But we haven’t necessarily evolved to tell real patterns apart from false ones, as Michael Shermer pointed out in Scientific American a few years ago:

Unfortunately, we did not evolve a Baloney Detection Network in the brain to distinguish between true and false patterns. We have no error-detection governor to modulate the pattern-recognition engine. (Thus the need for science with its self-correcting mechanisms of replication and peer review.) But such erroneous cognition is not likely to remove us from the gene pool and would therefore not have been selected against by evolution.

Shermer points to a study in Proceedings of the Royal Society B that examined the phenomenon and demonstrated that whenever the cost of believing in a false pattern (e.g., ghosts are real) is less than the cost of not believing in a real pattern (e.g., snakes of a specific color can kill), then natural selection will favor the belief in patterns, whether real or not. “Such patternicities, then, mean that people believe weird things because of our evolved need to believe nonweird things,” Shermer writes.

So if you believe in ghosts or witches or other things that go bump in the night, I guess you can blame evolution.