Do we all feel the same way about dirt?
Does dirt have different meanings for people
from different cultures?
In the West many of us are shunning the
traditional bar of soap for sophisticated antibacterial handwashing
and fragrant shower gels. The sophistication goes beyond the
physical. Lady Macbeth's exhortation to that "damned spot"
encapsulated the association of physical cleanliness and moral
'purity' four centuries ago.
Recently, researchers at the University of
Michigan have shown links between handwashing and the more
subtle psychological mechanisms involved in modern consumerism.
They found that handwashing
with soap eliminated post-decisional dissonance (the mild
discomfort people feel after making a choice between two CDs or
types of jam).
In other parts of the globe, soap doesn't even
feature in hygiene practices. Yet Dr Val Curtis says
handwashing with soap could save over a million deaths from
diarrhoeal disease per year in those regions. She is currently
evaluating an intervention to promote the behaviour in rural Indian
households, working with industry to make soap available at
In the West, we wouldn't dream of going out
without shoes on, and are mostly lucky enough to be able to afford
them. But in parts of Africa people go barefoot and risk picking up
parasitic worms or absorbing silicate particles from the soil
through their feet. In some people the silica particles cause
podoconiosis, a disabling swelling in the lower legs. Since only
some people react to the silicates in this way, a genetic cause is
likely, and Gail
Davey and colleagues are seeking to identify the gene
Despite the disease-causing agents it
harbours, soil is valued in many cultures. Paul Wenzel
Geissler noted that geophagy - the practice of eating soil - is
particularly common in pregnant women and primary-schoolchildren
who have depleted levels of iron in their blood. The iron in the
soil they ingest may be compensating for the deficiency.
He also described how earth-eating is an embedded
cultural practice. After childhood it is almost exclusively
women of reproductive age who eat earth. Earth symbolises female,
life-giving forces, fertility and the continuity of the lineage,
and the termite hills from which most earth eaten is taken
represent the home and the graves of ancestors.
Values and beliefs about dirt vary widely
across cultures. However, Val Curtis notes that the emotion of
disgust is common to nearly all of them, and is elicited by
similar groups of stimulus, including bodily excretions and waste,
living creatures such as lice and insects, decaying or spoilt food,
and other people in poor health. (See 'Dirt,
Disgust and Disease' by Valerie Curtis and Adam Biran
[PDF].) She suggests this aversion evolved to protect us from
potential sources of infection. Interestingly, disgust of other
people extends to those who commit crimes or violate social
'norms', and may serve to protect individuals and society by
ostracising and punishing 'social parasites'.
Val talks to Wellcome Collection's Lisa
Jamieson about the protective power of disgust (Packed
Lunch event, recorded live on 23 October 2009).
The spaces differ, but infections that thrive
in closed environments - such as hospitals, cruise ships,
military camps and slums - are common across the globe.
Wellcome-Trust funded researchers are using genetic approaches to
tackle two of these. Ian
Goodfellow is studying the molecular mechanisms of the
notorious norovirus to identify new methods of controlling and
preventing outbreaks, while researchers at the Wellcome Trust
Sanger Institute have developed a new method
that can detect single-letter changes in the genome of the superbug
MRSA, which will make it possible to precisely track its
transmission from person to person in hospitals and develop
targeted infection control strategies.