Num­ber game

Down to Earth - - SCIENCE -

THE NUM­BER of ver­te­brae in fast-mov­ing an­i­mals has re­mained more or less the same dur­ing the course of evo­lu­tion. This is be­cause any change would have ham­pered their speed and proved fa­tal. Nat­u­ral se­lec­tion avoided any such change. A large num­ber of mu­ta­tions is required to change the num­ber of ver­te­brae but its shape can change with a sin­gle mu­ta­tion. The num­ber of ver­te­brae in slow-mov­ing an­i­mals has seen a sig­nif­i­cant vari­a­tion be­cause their sur­vival is not de­pen­dent on their speed. PNAS, July 14

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