What is the evolutionary purpose of the topology of the human ear?
Humans do not have the ability to move their outer ear in response to sound. Many animals can do that, and use it to determine the source of the sound waves. Thus, human outer ears are equipped with many "hills and valleys". It does not provide amplification (because the waves can lose their energy bouncing around the ridges), but rather gives the brain more information about the sources' location in space. The brain calculates that location by determining minute differences in the time it takes for the sound to reach sensory cells in the inner ear on both sides. The shape basically attenuates the raw information. That way you get different properties of the sound wave that enters your ear depending on the angle at which it fell on you outer ear.