One of my lablings pointed out a cluster of mushrooms growing near the loading dock attached to our building the other day. Despite macroscopic and microscopic examination, we've been unable to identify it satisfactorily even to genus. The fact that it wasn't producing enough spores to obtain a print didn't help, and the few spores (fewer than two dozen) that I could find on the lamellae all had the same shape but their size and color varied. Some are colorless (hyaline), some are brown.
The gel above shows PCR products amplified from a small bit of the mushroom after drying. The first two bands are ITS and the second two are large subunit rDNA. Now that I have DNA, I can get the sequence and match it to known sequences. If anyone has sequenced this fungus before, we can identify it via molecular biology. If there's no exact match, the game still isn't over. Thanks to evolution, the sequences will still be closer to some fungi than others. If need be, I can do a quick alignment of similar sequences and then use phylogenetic software to determine to what the specimen is closest. With that much information, there's a very good chance it will be identified to species.
Next time someone tells you that they don't know anything practical that's based on evolutionary principles, ask them how they would have solved a problem like this if the fungus were eating the beams that support their house.