the brain does not do supervised learning—you are not given labeled data when you learn that one smell is an egg and another is a strawberry. Even before children learn the words egg and strawberry, they can clearly recognize that they are different. Second, backpropagation is biologically implausible. Backpropagation works by magically nudging millions of synapses simultaneously and in exactly the right amount to move the output of the network in the right direction. There is no conceivable way the brain could do this. So then how does the brain recognize patterns?
