... with those ridges and channels to direct sound in to your ear canal.

the cupped areas are there to capture sound from different directions; behind, front, low and up.

try putting your finger in different parts and you can hear a slight difference in the sound.

the ridges usually direct in the higher frequency as this might be the sound of rustling leaves or a branch snapping.

it's the human sonar alert system at work that has been in development for millions of years.