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Friday, 20 September 2013

The Scarab and the Stars

Earlier this year a scientific paper was published with the eyecatching title “Dung Beetles Use the Milky Way for Orientation”, which was widely reported in the mainstream media. The research has now been awarded one of the 2013 Ig Nobel Prizes – the “Joint Prize in Biology and Astronomy”.

Actually the result isn’t as outrageous as it sounds. The problem is that people focus on the symbolic associations of words, rather than the underlying thing a word is being used to describe. So a really basic image-processing task, because of the way it’s described, suddenly takes on cosmic or mystical significance. The mystical dimension is enhanced by the fact that the dung beetle, under its alternative name of Scarab, was a sacred symbol in ancient Egypt that has now become a favourite of New Agers.
Stars also have a New Age connection, via astrology. This is one of the reasons – alongside associations with UFOs and science fiction – that any mention of “the stars” is likely to provoke a giggle reflex in the general public. But this is because people are focusing on the layers of associations superimposed on words, rather than what words actually mean. Living in the modern world, we have a complex mental model of what a star is. But from a purely empirical perspective, the stars are just points of light in the sky.

Needless to say, a scarab beetle doesn’t carry along any intellectual baggage regarding the scientific and cultural associations of the stars. It just knows it can see them, because they’re there (in this respect, the beetle is closer to reality than most humans, who read all about outer space on the internet but rarely look up at the night sky). From the beetle’s point of view, there is survival value in being able to travel in a straight line. By trial and error over countless generations, it’s developed a way of doing this which involves looking up at the sky.

When humans navigate by the sun (during the daytime) or the stars (at night) they need to do some complex calculations, for a couple of reasons: (a) because they want to travel in a specific direction relative to the Earth’s surface, and (b) because journeys generally last several hours, during which time the positions of objects in the sky change. The beetle isn’t bothered by either of these considerations. It just sets off in a random direction, and wants to continue in that direction irrespective of the ups and downs of the terrain. And it only needs to travel a few metres, so objects in the sky aren’t going to move much.

The beetle doesn’t need a high resolution image of the sky – in fact quite the opposite. All it has to do is form a general impression of where the brightest part of the sky is, and then make sure this bright patch stays on the same relative bearing (“check sky – move forward – check sky – if bright patch has shifted counterclockwise turn slightly to the left – else if bright patch has shifted clockwise turn slightly to the right – repeat until destination is reached”).

But why does the beetle use the Milky Way? It’s a spiral galaxy consisting of a hundred billion stars, held together by gravity and dark matter. Isn’t that a rather sophisticated concept for an insect? Well no – the “concept” modern humans choose to attach to it is irrelevant. The Milky Way is just a distinctive feature in the night sky (in the clear skies of Egypt, where scarab beetles live). Having a low resolution imaging sensor, the beetle just looks for the brightest feature in its field of view. During the daytime, it uses the sun. At night, if there’s a moon, it uses the moon. If there isn’t a moon, it uses the Milky Way.

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