Echolocation has long been one thing that creationists show incredulity as to the ability for it to evolve.
I was watching a show the other day called "More than Human", in which they show people who can do unusual feats. One person that they had on was completely blind - and yet, they showed him mountain biking. The amazing thing was how he was doing it: echolocation.
As soon as I saw this, my initial reaction was disbelief. However, they set up a scenario to test him. They sat him down outside, and placed some objects near him - a tall metal pole, supporting what looked like a thin pane of cloth or plastic at the top over him - and asked him to identify his surroundings. He started off by recognizing the pole, describing it as a tall, thin metal object, and then went on to describe the boom mike that they were holding up to record the interview. He then identified a nearby tree, and then, turning upward, got confused... "is there a tent over me?"
Intrigued, I started researching the subject, and found
this. Apparently, a minimal level of echolocation is not only teachable to even non-blind people, but is part of our everyday senses. Most people are completely unaware of it. In one test, they had a number of blind people, and blindfolded sighted subjects, and asked them to approach as close to a board as possible without touching it. The blind people immediately were able to get within inches of it without touching; the sighted people took about 30 tries before they could get this level of accuracy. However, as they steadily removed their abilities to make and receive sounds, they steadily lost their ability to find the object, until everyone collided with the board every time.
So, I decided to run some tests for myself. I tried going to different rooms of my house, then spinning around until I had no clue where I was pointing, and then trying to orient myself with echolocation. However, I was continually frustrated. There was always at least some sort of faint sound in the house, and I could instinctively orient myself based on that sound, no matter how faint, without having to try and make echoes.
Then, that clued me in - if humans can orient themselves easily based on even faint sounds, then the only issue is whether humans can make echoes from objects strong enough to clue in on, and to separate multiple reflections. Quick tests in my bedroom showed that, with a proper clicking sound, you can get pretty clear echoes from most walls (I'm sure it would be a lot harder outdoors, though). So, there's only the complexity of the room to be able to learn to factor in.
If blind humans develop this ability even subconsciously on their own - and blind humans who actively use it (making clicking and snapping sounds with their mouths) can do things as dramatic as mountain biking - it seems quite clear that such a system can evolve from an organism which steadily moves to a niche or environment in which sight is no longer as effective. Furthermore, it appears to evolve from an already present system - namely, our ability to do direction finding on sound.
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"Illuminant light,
illuminate me."
™ Version 4.2