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from a snake charmer's basket, but from a forest of bowling pins. The axons appeared to be attached to the tops of the pins, which were supposed to represent the receptors (magnified a trillion times) on the olfactory epithelium; the receptors are proteins that decode the odorants and then send electrical signals up the axons for the brain to read and respond to appropriately. En route from the receptor sheet to the olfactory bulb, the axons are bundled into groups, each with its own message to be delivered to (synapsed at) the correct location on the olfactory bulb, the nerve tract leading into the brain. From there, the signals, now assembled into a pattern that represents a smell, are transmitted to two places. One is the limbic system, the brain's emotion and memory center. The other is the higher, thinking brain, where they meet up with signals sent from the other sensory systems, most of which have taken a far less circuitous route to get there.
    I drew half a Q-tip. This was supposed to be an olfactory bulb. The fat end faced outward. (The bulb tapers as it heads into the brain.) It was not a delicate Q-tip. The axon bundles

    hung off the bulb like a litter of piglets sucking on a sow's teats. So much for art class.
    My dog, Mel, a small, white terrier mix, was sprawled across the beanbag chair, all four legs pointing straight up. I scratched his belly and looked at my watch. Something was running around in my stomach. Hunger. Mel's belly morphed into the face of Dr. Cushing telling me, "You're going to have to watch the appetite. You may have to force yourself to eat." If an animal lost its sense of smell, would it die, since it didn't have a thinking brain to tell it sugarcoated half-truths about how life is worth living even without it? Probably. I've seen dogs in chemotherapy. It's not just nausea that puts them off food. While humans are driven by hope, longing, and dread (that is, future consequences of present acts), dogs live in the present. They do not force themselves to eat.
    My questions were like odor molecules flooding a functioning receptor sheet as that lucky person sniffed what promised to be a great meal. The more we sniff, the more we can't wait to dig in. I wondered why the smell of barbecued chicken was stronger than perfume, and why perfume fades so quickly, and why some smells are pleasant and others foul (and why some are delightful to me but not my husband, or revolting to us but transcendent to our dog—I'm thinking of deer scat), and why some smells are so hard to tell apart, and why people react so differently to them.
    And why we don't know.

5. An Underlying Logic
    T O UNDERSTAND SMELL, you first have to understand its primacy in human evolution. Smell is millions of years older than
Homo sapiens
, older even than man's most ancient ancestor, that nameless creature that first blundered onto land from the sea and in so doing made use of one of those evolutionary add-ons, a nose that could detect odor molecules in air as well as water.
    To understand evolution, you have to erase from your brain the notion that it is a logical process resulting in exquisitely designed species.
    Take the confusing jumble of cranial nerves in the human head. Paleontologist Neil Shubin likens them to the wiring and plumbing exposed when a building he once worked in was gutted. Constructed in 1896, it had undergone countless renovations. The pipes and wires, many of them damaged or useless or simply redundant, were good for something: they stored the record of how the building's mechanical infrastructure had evolved.
    This I can relate to. My 1880 house still has bits of the original tube-and-post wiring, as well as quite a few ungrounded outlets and other issues that make pulling a permit a dicey proposition. The plumbing is a combination of galvanized steel, copper, and lead. We don't update the infrastructure because we'd have to tear down the house to do it. The cobbled-together system keeps us warm in