What Are The Odds?

House Centipede

House Centipede

Centipedes are arthropods with many leg bearing segments that  vary from 15 to 191 segments in mature adults.  Out of thousands of species, none (zero!) have an even number of segments when they are mature. All have an odd number of leg bearing segments.   Biologists have puzzled over this odd observation trying to find explanations for this phenomena.

Immature centipedes exist that have an even number of segments and they are perfectly viable. Still, natural selection does not produce a centipede with an even number.  The best explanation is that a development process produces an odd number of segments. An elongation process then acts to add two segments at a time. Natural selection acts to preserve the development process, thus the odd number is preserved.

Ariel D. Chipman, Wallace Arthur and Michael Akam. A Double Segment Periodicity Underlies Segment Generation in Centipede Development. Current Biology, Vol. 14, 1250–1255, July 27, 2004
DOI 10.1016/j.cub.2004.07.026

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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One Response to What Are The Odds?

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