What is the first thing that comes to your mind when you hear the phrase “A work of art”?
Symphony in C minor by Beethoven?
The Starry Night by Vincent van Gogh?
David by Michelangelo?
Or God forbid, Baby by Justin Bieber?!
No offense to Beliebers reading this. Well, maybe some offense.
But seriously. Do you notice a pattern here? Historically, we humans have been obsessed with art that appeals solely to the visual and auditory senses.
When I first began my doctoral studies on the neuroscience of olfaction (the sense of smell), this artistic bias perplexed me to heaven and back. This is especially true considering the incredible evolutionary complexity of the olfactory system; making it perhaps the most interesting of all the human senses.
Let’s start with the nature of the stimulus itself. The visual system detects light that falls within a particular range of the light spectrum. The auditory system, similarly detects sounds, the frequencies of which lie within a certain auditory range. For the olfactory system, however, it is quite problematic to construct an “odorant spectrum”. Because odorants are horrendously diverse, one wouldn’t know where to start! Factors such as carbon chain length, volatility, alkalinity, acidity, and polarity are some of the properties one would have to consider, besides the presence of functional groups such as alcohols, thiols, ketones, amines, imines, acids, aldehydes, esters, pyrroles, pyrazines, alkenes, alkanes, ethers, sulphides, and nitriles. Think of your worst organic chemistry nightmare…and multiply it by a factor of 10000. The olfactory system solves this problem every tens of milliseconds!1
Lining the tiny bones inside the nose are millions of olfactory sensory neurons which actually detect odor chemicals in the air. And they accomplish this feat using a mechanism, which is equal parts complex, simple, and random.
Each olfactory neuron makes proteins called odorant receptors, which are transported into long hair-like structures called cilia found at the upper tip of each neuron. When an odorant enters the nose, it diffuses into a layer of mucus and binds to an odorant receptor on the cilia. This interaction kickstarts a cellular chain-reaction that eventually results in the generation of an electrical signal called an action potential. This electrical signal runs along the olfactory neuron’s cable wiring—technically known as its axon—and finally reaches the brain.2
Through an essentially random mechanism, each neuron makes a lot of just one type of odorant receptor, and no other.3 Each neuron has to “choose” to express one gene out of a possible set of around 1300 in mice, and around 800 in humans.4 However, many of the odorant receptor gene sequences are non-functional due to mutations that have accumulated along the course of evolutionary history, rendering them as pseudogenes (“fake” genes). This brings down the gene set to around 1100 in mice and around 300 in humans.5 Despite the large number of pseudogenes in the mammalian genome, odorant receptors constitute the largest family of receptor proteins ever known.6
1100 and 300 are large numbers, but just consider the number of volatile compounds in roasted coffee—900!7 Obviously we can’t detect all 900 of these volatiles, but if just a single event in our daily olfactory experience involves so many potential odorants, surely the number of odorants we experience in a lifetime must be tremendous. How do several hundred odorant receptors solve the problem of the sheer diversity of available odorants?
An easy way to understand how odorant receptors work would be to think of them as television antennae, and the odorants they detect as TV channel signals. A single TV channel (like PBS) may be picked up by many separate TV antennae (e.g. the antenna on my roof, another on my neighbor’s roof, and so on). Further, a single TV antenna can pick up many different TV channels. So also with odorant receptors: a particular odorant can be detected by many different receptors, and a single type of receptor can detect many different odorants. Thus, a single odorant can activate many olfactory neurons (to different degrees), each expressing a particular type of odorant receptor. En masse, this represent a kind of “code” resulting from a combination of neurons responding to a particular odorant. Since there are several hundred odorant receptors distributed randomly among millions of olfactory neurons, this results in a system capable of handling a huge diversity of odorants – each odorant activating a unique subset of olfactory neurons.
So how good exactly is this evolutionary design when put to the test? The most recent estimate indicates that humans with their modest number of 300 odorant receptors can discriminate a trillion olfactory stimuli.8
Let’s put that in perspective. Remember when Jesus said that the hair on your head are numbered (Luke 12:7)? One estimate suggests that the average number of hairs on an adult human head is on the order of 100,000.9 One trillion is when you count the hair on every single person living in the cities of Baltimore, Pittsburgh, San Diego and Kansas City, combined. That’s the number of odorants you can smell. And get this: one trillion is just the lower limit! Cue Mind Explosion.
As a Christian, my initial efforts to integrate my faith and my research left me rather disappointed, mostly because the Bible itself spoke far more of “sight” than “smell”:
“From heaven, the Lord looks down and sees* all mankind;
from his dwelling place he watches*
all who live on earth” – Psalm 33:13-14 (NIV)
“The people walking in darkness have seen* a great light” – Isaiah 9:2 (NIV)
“For we live by faith, not by sight*.” – 2 Corinthians 5:7 (NIV)
A keyword search on a Bible database for “see” yields 807 hits (NIV) compared to a paltry 26 hits for “smell”,“smelled”, “nostrils” and “odor” combined. This trend holds for all major English translations.
However, despite its meager number of occurrences in Scripture, the way biblical authors employ the sense of smell is truly remarkable. Here are three broad patterns regarding the sense of smell in Scripture:
1. God has a sense of “smell”!
When we usually think of the God of the Bible, we always picture him “watching over us”. But the biblical evidence that a divine “olfactory sense” exists is by far the most intriguing observation from the smelly parts of Scripture. That God can “smell” is indicated as early as the book of Genesis. Following the flood, when Noah comes out of the ark, he sacrifices burnt offerings on an altar. The first thing that God does is smell:
“The Lord smelled the pleasing aroma and said in his heart: “Never again will I curse the ground because of humans, even though every inclination of the human heart is evil from childhood. And never again will I destroy all living creatures, as I have done.” – Genesis 8:21
How poetic it is, that the God of all creation is moved to mercy by the smell of a simple burnt offering. Indeed, in humans, the olfactory system has very strong, overlapping neuronal connections with the amygdala and the hypothalamus – brain areas critical to the processing of emotion.10 11 It’s almost as if to say, “Wake up and smell the Imago Dei.”
2. Smell is closely associated with purity laws
The connection between olfaction and ancient Jewish concepts of purity may not be immediately obvious to our modern minds. And in many ways, our perceptions about what smells “holy” and “unholy” may be heavily influenced by cultural standards of “clean” and “unclean”. Nevertheless, one useful way of understanding ancient Jewish purity laws is to think about “clean” as the line demarcating life, physical wholeness, and order, from death, disease, and disorder. Noted social anthropologist Dame Mary Douglas sums up this distinction well:
“In short the idea of holiness was given an external physical expression in the wholeness of the body seen as a perfect container.” 12
In light of Levitical purity laws being seen through categorizations of “life” and “healthy” against “death” and “decay”, Martha’s warning to Jesus in John 11 not to roll away the stone covering her dead brother’s tomb is understandable:
“Roll the stone aside,” Jesus told them. But Martha, the dead man’s sister, protested, “Lord, he has been dead for four days. The smell will be terrible.” – John 11:39 (NLT)
In Martha’s eyes, Jesus was taking a huge risk in uncovering a decaying corpse, lest they all become unclean from the very odor of putrefying flesh. As it turns out, odors released during putrefaction (aptly named cadaverine and putrescine) are universally repulsive to humans, indicating the presence of nasal olfactory neurons specially tuned to detect these odorants.13 Surprisingly, these odorants are also detected by rodents, and elicits aversion even in fish; an evolutionary solution, meant to deter animals from contracting infection from carrion.14
3. Smell is mysterious
Since we rely so heavily on our eyes, it is obvious why vision has a sense of greater tangibility. That is why we have “eyewitnesses” and not “nosewitnesses”. But there is something mysterious about the sense of smell, in that you can’t always see what you smell (smell what I mean?). Smell is one of those things you perceive without a clear, volitional attempt to detect a stimulus. Because odors drift far from their source, carried along by air currents in the form of plumes, an odor can be detected long after the source has stopped emitting the odor, imbuing the sense of smell with an almost mystical attribute. And so, it is very interesting that in the Old Testament, the Hebrew word for spirit, ????? (rü’·akh) as its female noun form is derived from the primitive root verb, ????? (also rü’·akh) which means, you guessed it – to smell or perceive odor. This shared ethereality between smell and spirit is perhaps inaugurated during the creation narrative in Genesis:
“Then the LORD God formed a man from the dust of the ground and breathed into his nostrils the breath of life, and the man became a living being.” – Genesis 2:7
This usage brings up an interesting point, in that similar to how the intestines were considered to be the place of emotion and feeling, the nostrils were considered to be the residence of the spirit. Seemingly, this is ancient biology 101. Job, from the OT book of the same name, reinforces this point when he is questioned by his friends:
“…as long as my breath is in me, and the spirit of God is in my nostrils” – Job 27:3 (ESV)
And just to drive the point home, the fact that you can’t always determine when you might smell something as it wafts into your nasal passages, is uncannily similar to how even the Holy Spirit operates. In one of the most enlightening passages in the Bible, Jesus talks to the Pharisee Nicodemus about what being “born again” entails. In the exchange, Jesus explains the action of the Spirit by drawing an analogy to another category of stimuli that cannot be seen – sound:
“The wind blows wherever it pleases. You hear its sound, but you cannot tell where it comes from or where it is going. So it is with everyone born of the Spirit.” – John 3:8 (NIV)
My initial perplexity regarding why humans are skewed towards art that is visual and auditory still remains. And although recently there has been some progress on the olfactory art front, there is still a lot to learn on the science front. In fact, our unbalanced obsession with vision and sound is not restricted to the arts. Olfactory neuroscience was not “hot” or “hip” or “in” in the academic world till less than a decade ago. Which is why I had the profoundest of nerdy fangirl moments when I read the opening lines of The Perception of Odors (1982) by renowned olfaction researcher, the late Prof. Trygg Engen:
“Before odor pollution became a widespread problem, the sense of smell received only cursory attention in scientific treatments of its psychology and physiology. By contrast, writers like C. S. Lewis held this modality in higher esteem. As Lewis commented in a discussion of the value of perceptual experience: ‘Of landscapes, as of people, one becomes more tolerant after one’s twentieth year…We learn to look at them not in the flat but in depth as things to be burrowed into. It is not merely a question of lines and colors but of smells, sounds and tastes as well: I often wonder if professional artists don’t lose by seeing it in eye sensation only’ [Lewis and Executors of C. S. Lewis, 1966, 234].”15
I’ve always thought of the sense of smell as a more intimate sense than most other senses. For in smelling, the thing that we smell becomes almost a part of us. In detecting a smell, we essentially absorb the essence of the thing emanating it. This can play out badly of course – think of the last time you walked past a ripe overflowing dumpster. But conversely, imagine how delectably this can work. Imagine smelling your grandmother’s bread pudding.
The proof of the pudding is in the smelling, as much, and maybe more, than in the eating.
Is it any surprise then, that when a sincere heart offers anything to God, Scripture always mentions that it is accepted as a “pleasing aroma” to Him?
Advent is upon us. And so, this season, as Lewis suggests, maybe we shouldn’t just wake up and see the snow-capped mountains.
Maybe we shouldn’t just watch the chestnuts roasting on an open fire.
Maybe we shouldn’t just hear the silver bells ring-a-linging.
Maybe instead, we should close our eyes, wake up, and smell the aroma that is Frankincense and Myrrh.
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