@ Matthew: I can answer it, I think: putting that calcium there, that does nothing for survival. It is therefore a waste of resources. Those whales that form smaller vestigial leg bones will have just a slightly better survival margin. Given long enough, that would shrink those bones to elimination in the population. @ LEO: would you consider the evolution of the human body louse( that I linked to before) micro or macroevolution? http://www.nytimes.com/2007/03/08/he...e.4842725.html It's changed appendage shape to hold onto clothing better. Pretty significant change , given the scale of the critter involved. In fact, That's a good question for you: At what point would you consider microevolution to no longer be microevolution and be macroevolution? What would your yardstick be for that divide in definition?