This essay won joint third prize in a competition in The
Sceptics sometimes describe religion as a parasite on the human mind. In
the first part of the article, Religion as Parasite, I look at some of
the implications of this way of thinking for our understanding of
religion. In the second part, Parasite as Religion, I consider a more
literal and perhaps surprising possibility: that biological parasitism
may actually play a part in the formation of religious belief. Finally,
in the third part, I bring out some of the implications of these ideas
for our understanding of why religion exists.
Religion as parasite
A parasite is an organism that has adapted to live in or on another
organism, its host. We usually think of parasites as fairly large
creatures—worms or flukes, perhaps—but microscopic organisms such as
bacteria and viruses are also parasites. It is mainly these smaller
parasites that I have in mind here. The approach I take owes something
to Richard Dawkins's idea of memes but even more to Terrence Deacon's
view of language as a virus-like parasite that has evolved to be
particularly well adapted to the brains of children.
Deacon's theory of language
The fact that young children are able to learn languages with apparent
ease, Deacon suggests, does not mean that they have some extraordinary
innate linguistic ability, as some believe, but rather that languages
have evolved to be learnt easily by immature minds. He finds this more
plausible than Noam Chomsky's idea of a 'language organ' in the brain.
It is quite often said today that there is a 'God module' or 'religion
organ' in the brain, but this idea encounters many difficulties from
an evolutionary perspective, and the suggestion that religions are
parasites that have evolved to colonise the brains of children seems to
fit the facts better. Many religions enhance this effect by encouraging
their adherents to have large families: this is true of Judaism, Islam,
and Christianity, and of course the Roman Catholic proscription of
artificial contraception reinforces the tendency.
Similarities between language and religion
There are numerous similarities between language and religion. Both are
usually learnt in early childhood, literally at the mother's knee.
Religious beliefs inculcated in this way can be difficult to shake off,
just as one's 'mother tongue' is more persistent in the face of disuse
than are languages learnt in later life. Seen in this way, the
well-known if apocryphal Jesuit saying 'Give me a boy until he's seven
and he's mine for life' takes on a new significance.
Evolutionary aspects of language and religion
Species evolve, of course, and so do languages. Changes in vocabulary
and syntax mean that eventually new linguistic 'species' emerge which
are mutually incomprehensible. Something similar happens in religion:
Judaism, Christianity, and Islam share a common ancestry but conversion
from one to another is fairly rare—they can no longer 'interbreed'.
Religion and language both acquired in childhood
But the connection between language and religion goes deeper than this,
for religion depends on language for its continued existence. And, once
again, the association with childhood emerges here. Religious people are
often reproved by the non-religious, and even by some co-religionists,
for having a 'childish' view of God; and this is in a sense reflected in
references to God the Father (today often transformed by feminists into
God the Mother). If religion has evolved to be easily learnt by
children, this makes good sense. Is this perhaps what Jesus meant when
he said 'Except ye be converted, and become as little children, ye shall
not enter into the kingdom of heaven.' (Matthew 18, 3)?
Acquiring a religion involves to some extent learning a different
vocabulary and syntax: for example, the old Quaker use of 'thee' and, in
some Christian circles, phraseology such as believing 'on' Jesus instead
of the vernacular believing 'in'. Many religions take this further by
having a sacred language (Hebrew for Judaism, classical Arabic for
Islam, Sanskrit for Hinduism, Pali for Theravada Buddhism). Because
religions are generally ancient the languages they use are often
partially or wholly unintelligible to the laity and sometimes even the
clergy, but contrary to what religious modernisers suppose, this
linguistic remoteness is a strength, not a weakness. It adds to the
impressiveness of the religion for its adherents, and misguided attempts
to make religion more user-friendly by updating the language often have
the opposite effect from what is intended.
Different patterns of transmission
The acquisition of religion in childhood is an example of 'vertical'
transmission—transmission from parent to child. 'Horizontal'
transmission, from adult to adult by conversion, also occurs but is less
frequent. According to the late Ben Cullen, horizontal transmission of
parasites usually gives rise to more virulent infections than does
vertical transmission, and he thinks this is true of religion. So, for
example, the religions of traditional Australian societies, transmitted
vertically, were generally harmless or even beneficial, whereas a cult
like Aum Shinrikyo, transmitted horizontally, was lethal. This may
explain the fanaticism sometimes shown by converts to a religion: some
prominent Islamic terrorists have been converts.
Parasites not always bad
We generally think of parasites as something we want to avoid, but not
all parasites are harmful to their hosts. They may be neutral in their
effects or even beneficial, in which case they are usually referred to
as symbionts. In fact, symbiosis is extremely common—probably much
commoner than the production of disease. For example, termites have
bacteria in their gut which are needed to allow the termites to digest
cellulose. The bacteria are essential to termite life and the insects
ensure their survival: when a growing termite sheds its skin it is
immediately eaten either by the owner or by other members of the
Symbiosis in humans
Whether symbiosis occurs in humans is less certain, but it probably
does. There is a theory, admittedly not accepted by everyone, which
holds that the remarkable increase in allergic diseases in many
industrialised countries is related to our excessive hygiene. This
reduces our childhood exposure to parasites. Young children who
encounter a lot of viruses as a result of contact with other children
are less likely to develop allergies later, and other parasites may have
similar effects. Throughout most of our evolutionary prehistory we would
have been infested with parasites, and our immune systems evolved to
keep them under control though not to eliminate them. Perhaps, now that
our immune systems find themselves with time on their hands, they start
to misbehave, reacting excessively against things that they would
normally have ignored, such as dead dust mites.
Some experimenters have tested such ideas on themselves. By deliberately
infecting themselves with intestinal worms they have reduced the
severity of their asthma. And there is currently a plan to infect
patients suffering from multiple sclerosis with hookworm, since that
parasite appears to reduce the tendency to relapse in this disease.
Can religion be a beneficial parasite?
If it is true that exposure to biological parasites—in moderation—in
one's youth is protective against some diseases later in life, can we
apply the same logic to religion? Perhaps it is good for us to be
exposed to religion as children—always provided, of course, that it
is not in too virulent a form. So fanatical religions may be bad for
you, but less extreme varieties may be beneficial. Although it is
disputed, some evidence seems to show that having a religion tends
towards psychological and even physical health. Although a rigid
fundamentalist upbringing may be psychologically damaging, perhaps
youthful exposure to religious ideas, even if these are abandoned later,
may be good for you.
Mitochondria as parasites
Symbiosis probably began very early in our evolutionary history. The
mitochondria in our cells are structures—organelles, as they are
rather poetically known, meaning tiny organs—that were almost
certainly once free-living bacteria. At some time in the remote past
they became permanent denizens of 'advanced' cells (that is, cell
possessing a separate nucleus). They produce the energy which our cells
need in order to work; we could not exist without them. But this was a
later development in their function. Originally, they had a different
job to do: detoxifying oxygen.
Today we think of oxygen as essential to life, but it was not always so.
When oxygen first appeared on the planet it was a poison for most forms
of life. But certain bacteria acquired the ability to process it and
make it harmless. Later, some of these bacteria were incorporated into
other kinds of cells, where they eventually became, not merely useful,
but essential—not just as detoxifiers but as producers of energy. That
is where our mitochondria came from and why we still have them today.
They are symbionts. Now we cannot do without either mitochondria or
oxygen. We would die without them, and there are diseases caused by
malfunction of the mitochondria.
Religions: our psychological parasites?
Have religions become our psychological mitochondria—parasites that we
now cannot do without? If so, what function do they serve? Perhaps it is
to detoxify the fear of death. There is no general agreement about why
religions exist, but one popular idea is that they help people to cope
with the thought of death. Not everyone accepts this, but even if fear
of death is not what brought about religion at its inception it is
probably a major reason why it still exists today. We are presumably
unique among species on the planet in having an awareness of our coming
death, and Deacon thinks that this may be one of the most maladaptive
consequences of the way our brains have developed. Most people try to
put that awareness to the back of their minds and to distract themselves
in all kinds of ways. But those who truly believe in a religion usually
find at least a measure of consolation in their faith. Fear of death can
be seen as a psychological toxin, and infection with the religion
parasite may help us to detoxify it.
Parasites that induce religion?
To call religion a mind parasite is, at least partly, metaphorical. But
there may be a completely literal way which parasitism—biological
parasitism —is relevant to religion.
Parasites influence behaviour in various animals
Biological parasites can influence behaviour in animals and probably
also in humans in remarkable ways. In her book, 'Riddled with Life',
Marlene Zuk provides numerous examples of how this works. Here is just
one among many.
There is a tiny parasitic wasp in the forests of Costa
Rica which uses a certain type of spider as a host for its larva. The
spider normally spins an orb-type web like the kind you can see in your
garden in Britain. The wasp stings the spider, paralysing it
temporarily, while it lays an egg on its abdomen. After about half an
hour the spider recovers and carries on with its life as if nothing had
happened. But during the next two weeks the wasp larva hatches out and
sucks the spider's blood, until it is ready for the next stage in its
The night before the larva is due to form a pupa, the spider's
behaviour changes. Instead of spinning its usual spiral web, it produces
something like the top of a circus tent. In this the wasp pupa hangs
upside down, preparing to hatch out and continue its life cycle by
infecting another unfortunate spider.
This is too bad for the spider, but you may think that you have nothing
to worry about. You are a long way removed from arachnids in
evolutionary terms, after all. But wait: what about mammals? May these,
too, may have their behaviour modified by parasites? Almost certainly,
There is a well-known single-cell parasite called toxoplasma which
infects predators, such as cats. Cats get it by eating infected rats and
mice, who have in turn acquired it from the soil, where it arrived via
Rats have an innate fear of cats, for obvious reasons; it has been
selected for in evolution. When exposed to the smell of cat urine,
uninfected rats show a sensible aversion to it. Not so rats infected
with toxoplasma. Describing the experiments in which this altered
behaviour was demonstrated, Zuk says she found that watching a video of
the infected rats as they wandered into an area sprayed with cat urine
'was like seeing the heroine in a horror movie open the door to the
deserted barn while the maniac with the ax lurks behind it'.
Parasites affect human behaviour too?
So the toxoplasma parasite appears to be able to alter the rats' brains
so as to make them behave in a foolhardy way, which is bad for the rats
but good for the parasite. But now comes the really worrying bit. Human
infection rates with toxoplasmosis range from 22 to 84 per cent in
different countries. The parasite is acquired by eating undercooked
infected meat. As a rule it does not seem to cause obvious harm in
humans, though it can produce foetal abnormalities in pregnant women.
But are there any effects on human behaviour?
It seems there may be. Infected people are more accident-prone. Men who
are infected are more reserved, less trusting, and more likely to break
rules. Women, in contrast, are more out-going, trusting, and
self-assured. It is still not clear whether these differences are due
to the toxoplasma or are personality features that make certain people
more liable to infection. But if toxoplamosis is indeed responsible it
suggests that humans, though not the 'intended' target, can show the
same personality changes as do infected rats.
It is no doubt surprising, and potentially disturbing, to think that our
personality may be in part the result of our parasites. But should it
be? Many factors go to make us the kinds of people we are: our genes,
our upbringing, our early experiences, to name just a few. If someone
is better-natured as a result of infection with a parasite, is she
really any different from another person whose pleasant temperament is
the product of her genes? And would we wish to 'cure' the person if
eliminating their parasite made them mistrustful and unsociable?
If toxoplasmosis can make people kinder, it doesn't seem out of the
question that a parasite could make them religious. This might be an
unknown infection or it might even be toxoplasma itself. It would be
interesting to carry out a study to see if there is a connection
between a religious temperament and infection with toxoplasma. If there
is, the religion-as-parasite theory would be shown to be more literally
correct than anyone had supposed! Religious believers would be horrified
at the thought, but it doesn't seem to be out of the question.
Some implications for religion
Religion may be a form of mind parasite, as some secular critics
believe, but if it is as deeply inscribed in our brains, and perhaps
even in our nuclei, as the ideas I have described imply it is, the
attempt to eliminate it by pointing out its illogicality and lack of
credibility is unlikely to succeed. This is not necessarily, as many
seem to believe, because religion has been selected for during
evolution. Perhaps religion is simply a passenger, not usually doing us
much harm but not much good either.
There is an evolutionary analogy for this idea. It is likely that at
least some of our genes began life as viruses—parasites—and got
written into our cell nuclei during evolution. But many genes don't
appear to do anything. One of the most surprising discoveries in modern
genetics is that the function, if any, of most of our genes is unknown.
Only about 5 per cent of the human genome (the whole collection of genes
that we inherit from our parents) makes proteins that are used by the
organism. The other 95 per cent has no known function and has been
called junk DNA, although this is no longer a very respectable
scientific term, because perhaps it does have functions which we have
not yet discovered. Some of these 'junk DNA' genes do make proteins, but
these don't seem to do anything useful. The great majority of our DNA is
designated non-coding, which means that it apparently does nothing—it
is just a passenger. Perhaps religion is like this; perhaps it is
hitching a ride in our brains but not contributing much, either good or
bad. It is not essential to find a function for religion to explain its
Like our genomes, our minds are not carefully designed instruments that
function perfectly in all circumstances to give us objective truth, but
rather a collection of cobbled-together parts that don't always work as
we might expect. If some of the parts are really made from parasites
that have take up residence in us, it is hardly surprising if their
manifestations are sometimes rather difficult to understand.
Chomsky N. (1972). Language and Mind. Pantheon.
Cullen B. (1996). Parasite Ecology and the Evolution of Religion.
Deacon T. (1997). The Symbolic Species: The Co-evolution of Language
with the Human Brain. Allen Lane: The Penguin Press.
Zuk, M. (2007) Riddled With Life: Friendly Worms, Ladybug Sex, And The
Parasites That Make Us Who We Are. Harcourt.