(omni)science

How crabs find their way home

This article on Scientific American is getting a lot of attention everywhere. It is an attempt to shed some light on how fiddler crabs figure out how far they are from home and how to get back. John Layne and his fellow student at University of Cincinnati hypothesized that crabs calculate the number of steps taken away from home multiplied by the size of each step to measure the distance they have traveled.

In one of their experiments, they allowed some crabs to take normal strides but some were forced to walk on a slippery plastic sheet so that they could not take normal strides. The results, as expected, showed that the crabs on plastic sheet came short of reaching home because they kept falling whereas the others, with normal strides, had no problem reaching their burrows. It must be then that the crabs are carrying out some complex mathematical calculations to gauge their displacement from their burrows.

The problem I have with the study is the conclusion drawn from the experiment. I am not sure if one and one make two in this scenario. Because the crabs that slipped multiple times could not reach their burrows does not imply that they are carrying out calculations in their heads. To illustrate my point, imagine walking in the dark in some place foreign to you. You are not doing any mathematical calculations to determine how far you have gone. You can sense the distance you have traveled, and if you fall you will most likely lose orientation.

I am not claiming authority on the topic or that humans are somehow similar to crabs, and the paper has not been published yet but here is what I am thinking. Firstly, how can I be assured that there is no other system or ‘sensor’, like smell, shape, or something, that is helping these crabs take in information from the environment to assess their displacement? I know from rat maze experiments that their brains can develop an imprint of the map from trial and error.  Secondly, it seems that the experiments were done close to crab’s burrows, with which they should already have familiarity, sort of like walking in the neighborhood.  Thirdly, if they are indeed carrying out calculations, why can they not factor in how far they slipped?  Lastly, hypotheses can only be disproven not proven and the experiment conducted only works positively not negatively.