I'm no psychiatrist, but this smells like shyness, plain and simple. If this were some evolutionary defense mechanism, you wouldn't be attracted to pictures of women, either. But you are. You don't think you're attracted to "real" women because you're shy.
I'm generally a shy person, and it's a tough habit to break, but when you do (and it can be done!), you'll be glad you did.
If you just try to rationalize your situation and say "oh, I'm evolved to be this way," you're just dooming yourself to never change.