Sunday in Quito. Nine thousand feet up on the equator, the sky is clear, the parks filled with fruit vendors and picnicking families. Much of downtown is blocked from traffic, bikes fill the streets, and there is no exhaust. Absent exhaust, Quito smells like . . . nothing. Altitude kills the sense of smell. In the mountains, many physical realities make it difficult to smell our world—the dry air, and low air pressure; the high evaporation rate; the low density of aromas. On Sundays, when the buses spewing fumes are off the roads, this tropical city almost two miles high doesn’t smell like much. But I never noticed until I went looking for memories of smell from Quito, and couldn’t find any.

Memory is built by different sensory modalities but misled by those same senses. Memory explodes the myth of separate senses. When a young boy sees a backwards six, and says—that’s wrong, it’s too orange, six is redder—he is living the blurred boundaries of evolutionary history.
We are layers of history, our evolved selves, not fully traceable through species trees, because while species change and split all the time, traits do so even more messily. Traits may disappear from a lineage, only to reappear later, when selective pressures toggle a cascade of developmental switches—stick insects lost wings as they became twig mimics, but some have since regained wings, and the ability to fly. Those wings were buried deep. Or traits may simply appear, with no common history, in distantly related parts of the tree of life—neurotoxins in poison frogs and pitohui birds, syntax in parrots and people. Traits reticulate, and converge. Our ancient animal ancestors had a tripartite brain with the same three primary divisions that persist in all vertebrates today. In early fishes, those brain divisions—fore, mid, and hind—were loosely associated with smell, vision, and hearing, respectively. But selection acts in original ways, and as different senses have risen to prominence over time, where brains do what has moved around rather a lot.

In mammals, the cerebral hemispheres, part of the forebrain, have grown relative to other parts of the brain. With that increase in size of the primitively olfactory forebrain, the Age of Mammals became, de facto, the Age of Smell. To put it more precisely, the Age of Chemical Senses, but smell is a good stand-in for all of them, the most well-known of the others being aspects of taste. Watch your dog map the world by scent, or your cat pull olfactory information out of the air with his mouth slightly open, and be assured that other mammals rely strongly on smell. In those same expanding forebrains, we mammals were integrating olfaction with memory, and developing the corpus callosum, a powerful band of fibers that connects the two halves of our increasingly complex and asymmetric cerebral hemispheres. Mammals increase communication and connectivity in myriad ways—and we often do so through smell.

A small group of rogue mammals emerged some time ago with opposable thumbs, small snouts, and large eyes oriented to the fronts of our heads, however, and we primates, particularly the monkeys and apes, came to prioritize vision over smell. Those forward-facing eyes gave us binocular vision, and thus depth perception, but our big and growing forebrains were already dominant, so visual processing took over some of the neurological real estate that, long ago, was primarily the domain of smell.

Then we became human, spoken language arrived, and audition rose in the ranks of senses. Language processing showed up in the forebrain alongside visual processing, as well as pretty much all the other cognitive functions that contribute to making humans dominant on Earth—analysis, creativity, emotion, math, consciousness. All sitting in a prehistorically smell-focused area of the brain.

* * *

I was in Ecuador with twenty undergraduates, about to lead them in a six-week biological expedition around the country. We had known each other for months back on campus in the States, but this was day one of the trip. Not even—I had arrived late the night before, and most of my students had arrived a few days before me. The trip officially started the next day. It was day zero.

Planning to wander Quito alone that Sunday, I was happy to have three of my students join me. We headed vaguely towards “old town,” following a few short flights of stairs en route. Stairs in foreign cities are intriguing; they often go places you can’t know. In particular, old stone stairways are an invitation. Individual creations all, sometimes they’re co-opted for a new destination, sometimes they dead-end at a wall. I tend to follow them when I see them. Quito is long and thin, sprawling linearly in both directions from the old colonial center at its heart. One of the city’s boundaries is the Pichincha volcano, which has, of late, been spreading ash over the city every few years. On this day in early February, the 60-degree weather felt warm to us, newly arrived from the North, and we explored all day, slowly getting acclimated. By four, we were talking about heading back to the hostel, when we saw the most enticing flight of stairs yet.

It was twenty feet wide at the bottom, grand steep flights plateauing every thirty stairs or so before climbing again, the stairs visibly narrowing as they disappeared from view. We began climbing, stopping to admire the view of the Virgin, the tall winged statue visible from many points in the city, or to catch our breath. At every plateau, a new vantage. Short stone walls on both sides blocked views into ramshackle residences, a school. It was quiet and still—no people at all, except for one man who passed us near the top. I said “buenos” to him, short for buenos dias, a friendly, humanizing gesture that is nearly always reciprocated by strangers in Latin America. He looked at us and continued on without words. Shortly thereafter, we viewed a street ahead and decided to turn there and head North, towards our temporary home. Out of nowhere, two men, one flashing a long knife, run up to us. The one holding the knife, straight out of Hollywood in a dark hoodie with two long scars across his face, approaches Michelle. She is our photographer, and has both a backpack and a nice DSLR camera around her neck. The other man runs up to Jeremy and gestures for him to hand over his bag. Jeremy is far bigger and stronger than the guy on him, and he has a knife of his own in his pocket, but Scarface has his knife too close to Michelle for Jeremy to do anything but hand over his bag. I have nothing on me—nothing obvious, some cash and id flat in my pocket—nor does Arthur, and I stand, back towards the wall, hands out, palms up, watching. Arthur, with martial arts training, has adopted a similar pose across the way—non-threatening, docile—and we will learn later that he has his eye trained on a large dog that is at risk of joining the fray. I do not see the dog.
[Continued in Issue 123]