Why parasites are like car thieves

This is the first popular article I ever published – in a South African newspaper when I was doing my PhD. Written in 1996. It is a little dated as the arms race has moved on. But the evolutionary principles and the anti-theft principles remain sound.

The evolutionary war between animals and their parasites can teach us a lot about how to foil car thieves. But it is important to remember that no device, however ingenious, is foolproof forever – small victories are the best one can hope for.

I am amazed at the short-sightedness of motorists who claim to own the ultimate anti-theft device. A lesson from biology will show why an ultimate device is a fallacy.

All animals, including humans, are host to millions of bacteria, viruses, fungi and parasites and have evolved their own defences. Successful new types of resistance will spread through the population by natural selection: those with the resistance genes live longer and produce more offspring than those without.

This process is by no means one-sided. If some parasites have ways of countering the resistance, these too will be favoured by the same process. The parasites that avoid being fought off by the body live longest and reproduce the most – ensuring the spread of the genes.

New resistance in the host and new virulence in the parasite evolve at rates that depend on how common the resistance gene or the parasites are. If a parasite is very rare, resistance to it will evolve slowly, but common parasites drive fast evolution for resistance. Similarly, if the resistance is only present in a few hosts, selection on the parasite to evolve new ways of overcoming resistance will be weak.

Biologists call the vicious evolutionary cycle between parasites and their hosts the Red Queen’s race, after the character in Alice in Wonderland who told Alice “here it takes all the running you can do just to stay in one place”. [South Africa’s] local car-theft industry provides an interesting Red Queen’s race of its own.

When car theft was rare, people often left their cars unlocked and the windows open. As theft became more of a problem, people started locking their car doors and closing the windows. Car thieves quickly learned how to break into a vehicle without drawing unwanted attention. As thefts increase, incentives to develop new ways of keeping cars secure got stronger.

Car alarms underwent a long and complex evolution of their own. At first even the simplest alarms succeeded because they were rare and thieves had not learned to deal with them. Then, because they worked, many drivers installed alarms. As more thieves were faced with the problem of car alarms, information on how to neutralise them spread so quickly that today an alarm does not guarantee the safety of the car.

Immobilisers followed as similar route. They were effective at first, but then they became the norm: if you do not have an immobiliser, your car will most likely be in a chop shop by the weekend. But if you do have an immobiliser, there is no guarantee it will not. The best immobilisers are installed in such a way that the thief is unable to short-circuit them. The best way to keep this secret is to ensure that your immobiliser’s vulnerabilities are not in the same place as every other car’s.

Recent responses from car owners to our world-champion vehicle removal service include steering locks, gearshift locks and wheel clamps. They work when they are used by few people, but if something works really well then people tend to rush out and buy it. This is good for the genius who invented the defence but bad for the people who buy it. As more people installed steering-wheel locks, criminals began to steal the steering wheel from one car to drive another away.

Hijacking is the new trump card of car thieves. It is symptomatic of a society where cars are better secured than the banks of some nations. Now it is up to car owners to respond. The future already looks bright for the makers of bullet-proof glass and satellite tracking devices.

The important point is that no device is secure forever: the effectiveness of a strategy against theft decreases with its popularity because it soon profits thieves to work out flaws in the system. Novelty is the best way to fool the criminal mind.

Like car owners, doctors have long suffered from the fallacy that we can develop ultimate solutions to diseases. Developing drugs that counteract a parasite puts pressure on the bug to evolve new responses. Malaria is a good example.

Europeans, with no resistance to malaria, used chloroquine to avoid the fatal disease. Until recently, you popped a few chloroquine tablets before going to the lowveld to look at lions (and feed mosquitoes) and worried no more. Fortunately for the malaria parasite, but not for people, there were some very rare genes for resistance to chloroquine. As more humans took the pills, only the tiny proportion of malaria parasites that were not bothered by chloroquine prospered. With every generation of malaria parasites, the resistant ones produced more offspring, resulting in a higher proportion of resistant parasites. Today, chloroquine is hopelessly inadequate if you want to avoid malaria.

Chloroquine resistance is a very serious medical problem brought about by a violation of the first rule of car security: a suite of responses (drugs or anti-theft devices) are better than one general one. It is difficult and unprofitable for the parasite or thief (what is the difference anyway?) to learn or evolve ways to deal with all of them.

Rob Brooks

I am an evolutionary biologist who thinks about sex for a living. Things I have thought and written about include the evolution of mate choice, the costs of being attractive, the reason animals age and the links between sex, diet, obesity and death. Follow @Brooks_Rob on Twitter.

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