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Jason G. Goldman
From monkeys to humans, grooming is an important way to win favours and earn
social standing. For babies, it can also be the difference between life and
death.
When you run your hands through your lover s hair, you re probably not thinking
about your place in the social hierarchy. Give your team-mate or colleague a
pat on the back after a setback, and the chances are you re not consciously
seeking to change the mix of signalling chemicals in their brain. It may not
seem like it, but these socially important rituals and others like them predate
the time our species first walked the African savannah.
Human behaviours that involve physical social contact have a lot more in common
with social grooming activities we typically associate with other species than
we might initially think. When rhesus monkeys or chimpanzees pick through their
friends' fur, they're not just helping them remove dirt and parasites from hard
to reach spots. There is undoubtedly a hygienic benefit, but this behaviour,
which animal behaviour researchers call allogrooming , has far greater
significance. The gelada baboon, for example, spends 17% of its waking hours
doing this when just 1% would be sufficient to achieve good hygiene, according
to one estimate. Allogrooming is the currency of what primatologist Frans de
Waal calls the "marketplace of services" in chimpanzee life: it defines the
social hierarchy, which in turn dictates access to food, sex, and social
support.
For example, one chimpanzee is more likely to share food with another that has
previously groomed it. Grooming also serves to ease tensions in a chimp troop
following an aggressive situation. One of the most complex forms of
reconciliation among chimpanzees occurs when two rival males reach a point of
stalemate, neither backing down nor escalating the aggressive interaction.
Sometimes, a female breaks the deadlock and eases the tension by grooming first
one male, and then the other, until the two become relaxed enough to end what
amounted to an angry staring contest.
According to anthropologist Robin Dunbar, this works because grooming
stimulates the release of endorphins opiates produced by the brain that
trigger feelings of relaxation by lowering the heart rate, reducing overt
nervous behaviours like scratching, and even bringing on sleep. Female chimps
that use grooming as a peacekeeping strategy may also experience their own rush
of endorphins and enjoy many of the same benefits.
Humans, lacking the fur of our more hirsute evolutionary cousins, had to find a
replacement for allogrooming. Like grooming, gossip establishes and maintains
our place in the social hierarchy. Also like grooming, the social information
that makes up gossip is itself a form of currency in human culture. Or, at
least, that's the theory put forward by Dunbar. He argued, in his book
Grooming, Gossip and the Evolution of Language, that the faculty of language
allowed our species to substitute gossip for grooming.
Pleasure principle
But grooming, and related forms of social physical contact, hasn't gone away
entirely. While we humans don't make a habit of picking through our friends'
hair for parasites nurses searching for lice on the first day of summer camp
notwithstanding the truth is that gossip hasn't completely replaced our need
for physical touch. Indeed, words don't always make adequate tools for
communicating our feelings. Far more can be said by a heartfelt hug or squeeze
on the shoulder after a friend suffers the loss of a relative than through
words.
In the same way, one's love and desire for a partner can be conveyed with a
seductive stroke far more effectively than even the words "I want you" ever
could. Indeed, Dunbar writes, "the physical stimulation of touch tells us more
about the inner feelings of the 'groomer', and in a more direct way" than words
are able. And those forms of touch stimulate within us the same endorphin
release that chimpanzees enjoy during social grooming.
Some scientists have even gone as far as calling the skin a "social organ".
This makes good intuitive sense: we both crave touch and are repulsed by it
when it is unwanted, uninvited, or inappropriate. Even simple, brief touches on
a hand or arm can have tremendous effects. India Morrison and colleagues at
Goteborg University, in Sweden, have presented a laundry list of such findings.
Hand-on-hand touches by librarians and salespersons have, for example, been
found to lead to more favourable impressions of libraries and shops. People
perceive others as more attractive following even a simple, non-sexual touch,
and as a result are more likely to act altruistically by returning change left
in a pay phone, giving bigger tips in restaurants, or giving away a cigarette
to a stranger.
And yet these effects might be thought of as simple parlour tricks compared to
the power that touch has between lovers, or between parents and their children.
In one study, US psychologists investigated social grooming in humans by asking
participants to indicate their closest emotional relationship and report
behaviours such as running their fingers through the person s hair, wiping away
their tears, scratching their back and non-sexual massage. They found levels of
relationship satisfaction and trust were both positively correlated with
self-reported grooming frequency among romantic partners. And one finding
hinted at a causal relationship: people who were more anxious about their
relationships "groomed" their partners more often than those who felt more
secure with their partners, suggesting that grooming may serve to reduce
relationship-related anxiety and to promote the development of romantic bonds.
The pattern was true both for men and women.
Survival instinct
Babies also crave touch. It has long been known among animal behaviour
researchers that physical contact is critical for proper social and emotional
development. When developmental psychologist Harry Harlow deprived infant
rhesus monkeys of access to a monkey mother in his 1950s experiments at the
University of Wisconsin-Madison, they became withdrawn, depressed, and anxious.
They refused food, and entered into what he called a "state of emotional
shock." When allowed access to a surrogate mother, the infant monkeys
overwhelmingly chose the tactile sensations provided by a doll covered by terry
cloth over a wire doll that provided food and water. The young monkeys
preferred the comfort of even an inanimate mother's touch to physical
sustenance.
More recent research with rats replicates Harlow's early findings. Canadian
researchers found that when infant rats were licked and groomed more by their
mothers, they grew up to be relatively well adjusted. But their counterparts
who were deprived of grooming often grew up, like Harlow's monkeys, to be
anxious and fearful. Touch-deprived rats also had weakened immune systems. It
appears as if touch helps to maintain not only social and emotional health, but
also physical health.
According to the World Health Organization, more than 20 million infants each
year are born pre-term, which means that they weigh less than 5lb 8oz (2.5kg)
upon birth. These babies have increased risk of death in the first few weeks of
life. Caring for low-birth-weight infants in hospitals is expensive and
requires highly skilled personnel, however research suggests a therapy called
kangaroo care is both cheaper and just as effective. Originally developed in
Bogota, Colombia, as a way of keeping preterm infants warm in overcrowded
nurseries, the practice is deceptively simple. The mother or father simply has
to repeatedly place their baby against their bare chest, ideally for prolonged
periods.
A meta-analysis of three randomised control trials (the gold standard in
biomedical research), conducted in Colombia, Bangladesh, Ethiopia, Indonesia
and Mexico found that babies born weighing 4lb 6oz (2kg) or less given kangaroo
care in the first week of life were 51% less likely to die in the first four
weeks after birth, compared with infants who received standard care.
Other research has found that kangaroo care helps to stabilise preterm infants'
vital signs, maintains adequate oxygen levels in the blood, and helps them to
sleep better. It also reduces crying, increases weight gain, and allows preterm
infants to spend fewer days in incubators, ultimately allowing them to be
discharged from neonatal intensive care units sooner than those who are treated
with conventional care.
All primates, from monkey to man, rely on social touch. Among non-human
primates, grooming is a tool used to garner favours, earn social standing, and
increase access to resources. Gossip may have replaced parasite removal as a
mechanism for defining and enhancing one's place in human society, but the
desire to be touched is carved so deeply within our primate heritage that it
remained even as we shed our fur. For an infant born prematurely, social touch
can literally mean the difference between life and death. For the rest of us,
being touched simply reminds us that we are loved.