The scent of petrol – gasoline – ought empirically to be the same worldwide. There are slight variations in strength and additives, but, rationally, it should match the same chemical formula. To generalise: my experience of smelling petrol ought to be consistent wherever I am.
So I’m puzzled why it isn’t. When I return to my mother’s lifelong home in Gloucestershire, walk down the drive to the car-port, and she starts her car, the scent is instantly and uniquely evocative of my childhood. And it’s significantly different from the odour emitted by the same car, filled with identical petrol, when she visits our home in the North of England. It’s the remembered scent of my grandmother’s MG TD, kept in the same place, although that had the additional scent of leather upholstery. And leaded petrol.
Maybe it’s a kind of ‘cocktail’ effect? It’s not – I’m sure – some type of psychological overlay of associated memories. It’s as if the carrier is different. The air as distinctly different as Brandy from Whisky.
Certainly air has recognisably evocative qualities. Just as we hardly notice the subtle differences in flavour between glasses of water from different sources, and imagine it to be merely colourless, odourless and flavour-free – unless they’ve been spraying slurry on the fields, or a nearby bonfire is filling the air with smoke; our brains seem to filter out the subtle nuances of the sensory information conveyed by the air we breathe. We probably recognise the scent of cities and rural landscapes after snowfall or summer rain, but dismiss them as givens. That phenomenon was given a name in a journal article in Nature in March 1964, by IJ Bear and RG Thomas.
The noun they coined was ‘petrichor’ – etymologically derived from the root ‘petro’ – which relates to rocks, and is also the derivation of ‘petrol’ – and ‘ichor’ which is the word which describes the fluid said to run in the veins and arteries of the Classical Gods, and – medically – the almost colourless exudate of wounds and sores. Personally I’d have preferred it to have been synthesised from ‘petri-’ (relating still to stones) and ‘chor’, which is the German word for choir. Which would make petrichor something akin to the song of the earth. Which evokes Gustav Mahler’s setting of Chinese poems, ‘Das Lied von der Erde.’
Even when Cotswold soil is dry, my mother’s home bears the scent of the ochrish, stony clay which entailed hiring a mechanical digger when she wished to bury her red setter’s body in the garden. Wild garlic thrives in the leaf-mould at the bottom of the drive, jostling for space amongst the spring bluebells. In summer the Linden trees at the roadside buzz with bees plundering their sweet scented flowers, and woodsmoke from village hearths perfumes the air as the evenings chill in autumn. In winter the scent of conifers decants a light incense to the dry cold of frosted snow across the lawns. But, always, her petrol smells unique.
So many scents return me to past moments, but they don’t necessarily recall associated memories. No rational process of visualisation, nor of attempts towards verbal definition, is necessary. These olfactory stimuli are sufficient in themselves. Without question, they are consciousness-altering, as nostalgic as yellowing photographs in the black-paged album with its white-chinagraph- pencilled captions. Mood-changing. Exciting beyond reason.
Undeniably: there’s always a temptation to recapture and preserve these seemingly significant sensory experiences, but adding information to provoke other senses or enlighten reason diminishes the power of the scent to move me through these wormholes in time. Trying to give meaning to the effect of an odour is a destructive act of intellectual foolishness. Significance does not always connect with any logical meaning.
Perception is very idiosyncratic. It’s hard to separate associative learning – Pavlov’s classic conditioned response – from instinctive reflexes. To a foot fetishist, an odour which might cause all but the most ardent cheese-gourmet to retch acquires an arousing meaning. Even unperceived odours can affect us chemically, sparking the secretion of hormones which alter our behaviour without our having the slightest awareness. It’s thought to be the mechanism of sexual chemistry: the subtle attraction of compatibility. Colour-blindness is just an extreme example of the phenomenon that it is likely that no two individuals share exactly the same colour perception. The evolutionary biochemistry of mate selection possibly dictates different preferences between individuals for odours most predictive of reproductive success. Different strokes for different folks.
For Proust it was the flavour of a Madeleine dipped in tea. Flavour is distinctly related to odour, although the component of tactile sensitisation adds a further dimension. Food researchers spend a lot of time discussing ‘mouth-feel’. Possibly our experience of scent is wider than that of flavour. Common sense dictates that we would rather reject something on the grounds of its odour than risk poisoning by putting it in our mouths. Not to mention the problems inherent in small fishbones and the unwanted parts of an artichoke.
There’s something volatile about visual and sonic stimuli. Memories are less commonly evoked by sights or sounds, and even more rarely by the tactile sensations of texture, temperature and pressure. Scents and the sense of smell seem to trump the other senses in guiding our behaviour.
More than other animals, humans delight in manipulating natural things for carefully calculated purposes. We make ‘art’ (a word which is cognate with ‘artificial’) to appeal to visual and tactile senses, through painting, drawing, photography, cinematography and sculpture. We create music, affecting one another through the sense of hearing, and the food and drink of fine dining have become a complex and ritualised part of human social interaction. These activities are all pretty much ‘above the line’ – where we recognise how deliberately others appear above the parapet separating our private selves from our presented self-expression.
The art of the perfumier is more subtle. Perhaps you are already aware that retail environments manipulate consumers by injecting artificial odours of fresh roasted coffee and newly baked bread into air conditioning systems. We are exhorted to ‘fragrance’ our homes, to deodorise our bodies and mask our animal scents with sophisticated synthetic chemical mixtures and compounds.
I feel sorry for pet dogs. The reek of personal care products must create the olfactory equivalent of the hearing affliction of tinnitus. That dogs find the odour of cancer both detectable and offensive is unsurprising. Experienced nurses can often smell the specific keynote of particular infections. Odours are important in keeping our species healthy. We are naturally revolted by the odours of death, corruption and decay. Halitosis constitutes a great social disadvantage, so we devise mouthwashes to conceal the underlying problem as much as to cure it.
Research has established that the scent of our bodies, and how it affects others is cyclically linked to fertility. The propensity towards the provocation of sexual desire in women through exposure to both perceptible and imperceptible male odours increases as their cycles reach the peak fertile period. This is despite the fact that many primates, and especially humans, engage in sexual activity when reproduction is less likely, whereas other animals tend to restrict it to times of assured reproductive success.
Some ethologists have suggested that it is the absence of predators and the relative availability of resources which enables humans to engage in sexual activities for social and recreational strategies. Regardless of the validity of this theory, it seems to be a recipe for trouble.
Not only do we manipulate the way we look with cosmetic surgery and paint, potions and lotions, but we obliterate all the natural scent signals our bodies ought to be generating. As a result we probably miss being repelled by people with whom we are incompatible, and never notice those with whom an intimate relationship would be most fulfilling.
Maybe we don’t think about how we smell because words are inadequate to explain the almost primal effects scents have on our behaviour. Even the unspeakable odours that defy all rational explanation!