46 | New Scientist | 12 October 2019
one of the volunteers asked if she could have
the contact details for sweaty T-shirt No6.
Even as we are learning more about the
subtle scent cues we send and receive, genetic
studies now indicate that humanity as
a whole is losing touch with its olfactory
communication channel – and not just
because we are evolving to stink less.
A significant proportion of people have
a selective anosmia, or loss of smell, for the
major compounds found in armpit odour,
says Natsch. For example, up to 40 per cent
are unable to smell androstenone, a putative
sex pheromone. “There seems to be an
accelerated evolutionary loss of the ability
to smell body odours,” he says.Missed messages
Intriguingly, modern languages may reflect
this loss. Most, like English, lack a decent
lexicon for smell. We have relatively few
words to describe specific scents compared
with languages such as Umpila, which is
spoken by a traditionally hunter-gatherer
community in Australia. “Maybe in that kind
of environment smell is a much more salient
signal. That’s why you end up with a language
for it,” says Majid. Hunter-gatherers also don’t
share our enthusiasm for disguising their
bodily smells, she notes.
That loss goes both ways. Having a lexicon
of smell enhances people’s appreciation of this
unsung sense. “Once you have it in language,
it’s more part of your conscious awareness,”
says Majid. Without this awareness, we are
probably missing out on some of the subtlesignals that body odour transmits about
others. On the other hand, with the evolution
of language, perhaps humans didn’t need
to rely on smell as much as other mammals
because we could verbalise some of the
messages it carries. But Ferdenzi, for one,
is unconvinced. “Language and body odour
are totally different ways of communicating,”
she says. “There is this subliminal effect of
olfaction that we absolutely cannot control.”
Whatever the reasons for our changing
relationship with human smells, we may be
paying a price. Anosmia – which affects around
5 per cent of people – is an extreme version, but
we know that it can undermine quality of life
and increase risk for depression. And smell
fortifies our relationships in ways we may only
appreciate once the people, or their scents, are
gone. When Thomas Hummel at the Technical
University Dresden asked anosmics which
odours they missed most, many said it was
the smell of their loved ones.
But there are things we can do. We can all
learn to smell more “mindfully”, according
to Hummel. In his efforts to help people
with anosmia, he found that simply sniffing
odours consciously and regularly radically
improves anyone’s ability to smell. “It alerts
people to smell smells,” he says.
Even if we could do more to appreciate their
influence or stop taking them for granted,
sometimes the power of human scents is
undeniable. “It’s not just an ancient sense we
don’t use anymore,” says Ferdenzi. Just ask
sweaty T-shirt No6. ❚Kate Douglas is a features editor at New ScientistOur noses are home to about
6 million smell receptors of some
400 different types – compared
with just three kinds for vision.
Genetic variations affect the way
these work, and there are five such
variations, on average, per receptor.
Most odours activate several
receptors, but a change in a single
receptor is often enough to alter the
way we perceive particular smells,
including their pleasantness.
It isn’t easy to measure
something as subjective as smell.
Having people describe aspects
of certain odours such as strength,
pleasantness and quality has
revealed that we can perceive
similar compounds very differently.
“There’s a lot of variation
among people in odours that
have been tested,” says Casey
Trimmer, a scientist at fragrance
company Firmenich.
That’s just the first level of smell
perception. “A whole other level
happens in the brain,” says Trimmer.
How you perceive smells depends
on exposure, expectations and
associations, but there are probably
some universals. Asifa Majid
at the University of York, UK,
has found that Westerners and
hunter-gatherers from Malaysia
display similar facial expressions
in response to particular smelly
compounds. “That suggests there
may be some shared element
to what we find pleasant and
unpleasant,” she says.
Having a particularly acute sense
of smell – which is more common in
women than men – also influences
our perceptions. “As you find an
odour more intense, you tend to
find it less pleasant,” says Trimmer.
She thinks that may be caused by
overstimulation, but notes that
some odours, such as vanillin, don’t
offend even at high concentrations.CAN YOU
SMELL THAT?Mothers can
identify their
babies by
scent within
minutes of
giving birthJGI
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