Friday, June 22, 2012


Here is one of the most puzzling questions about the desert; why do cactus have spines? The evolutionary explanation is that they are modified leaves, but why not just lose the leaves altogether? Why long sharp spines? The few animals that eat cactus, eat the spines as well as everything else. But there are precious few animals that eat cactus with or without spines. In fact, almost every plant that grows in the desert, except some grasses and ground hugging plants, have some kind of sharp pointy things growing on them. Why? What possible evolutionary advantage is there to a defensive system for which there is no enemy?


  1. Even more creatures would eat them if they did not have the spines.

  2. A very unscientific WILD guess — are the spines some sort of modified "sweating" mechanism? No desert plant could survive by losing much water, but sweat is also a purifier, and plants may need that, so the spines are a compromise? (I suspect that sweating is more animal than vegetable, but not exclusively so?)