Evolutionary Enigma

The most puzzling example in evolution for me is an Australian frog. When the father sits on the eggs, the coatings liquefy and the tadpoles are released. They then curl up inside pouches on his hips. Three separate behaviours had to evolve together. I can see how a small pouch could evolve into a large one, but not how a flat surface could evolve into a pouch. As the creations might say, what use is 1/10 of a pouch?

~ Roedy (1948-02-04 age:69)