We're born to be wild
For more than 200 generations, they have not ventured outside. Yet a remarkable new experiment, which has tantalising implications for human behaviour, has discovered that laboratory-bred rats never forget how to survive in the wild.
Despite not knowing what the natural world looks, smells or even feels like, a group of rodents whose forebears have been kept in cages for the past 96 years showed that their ancient genetic impulses quickly surfaced.
Within hours of being freed, the rats started to return to their 'wild' ways, burrowing and following ancient mating instincts, behaviour which had never been possible when they were caged captives.
People have long thought that the trappings of civilisations could be quickly discarded when mammals were confronted with the necessities of survival.
But far from witnessing a Lord of the Flies -style reversion to a violent, cruel society, the rats formed more of a hierarchical order based on age, showing respect for the older animals and better organisational skills.
Dr Manuel Berdoy, a zoologist at Oxford University Veterinary Services, who put 75 rats into a farmyard and watched and filmed their reactions over six months, said that the results threw light on how our innate instincts work.
'The released rats quickly showed the ghost of their wild ancestors still lies beneath the wild coat of the lab rat, even after so many years of selective breeding [to favour more docile animals],' he said.
'Our rats found water, food and bolt holes almost immediately; within days they had started to establish social hierarchies, and within weeks they had a wide-ranging pattern of runs criss-crossing the colony.'
While Berdoy is wary of making too many links between species, he said: 'There are lots of similarities between rats and humans in that we are successful social omnivores. Certainly they had similar problems to resolve and some of them they resolved in a similar way.'
There could be no greater change of environment for a rat than the difference between the outdoors and a research laboratory. Lab rats are kept in plastic cages - normally with straw, maybe with cardboard tubes to hide in - that are cleaned out at least weekly. There is a constant supply of nutritionally balanced pellets for food, lighting is artificial and on timers, and the heating is controlled to within a few degrees.
In the wild, on a tennis court-sized enclosure, they had a terrain of grass, stones and straw bales, and obstacles like ladders. There was a supply of pellets but they also discovered and tasted berries, an apple, a snail, an egg and even a dead bird. The lights went out when the sun set, and the weather fluctuated from sunshine to rainstorms.
The white and Lister-hooded rats in the experiment had been bred and kept in labs since such testing began in 1908 - which, given that rats can breed every three months, makes them at least the 200th generation.
The conclusions are obvious, according to Berdoy. 'We have taken the animal from the wild, but we have not taken all the wild from the animal.'
His experiment unfolds in an award-winning internet film which has attracted interest from several TV companies. The first thing the released rats did was to venture out to explore the new terrain - led by the male hooded rats which, before they did anything, went to find their female white companions.
After that the animals soon found water, and began experimenting with new foods, a far cry from the pel lets their many ancestors lived on in labs.
It then took little time for the rats to start finding burrows for protection - even though they would never have been threatened in such ways before.
Even after six months, the lab rats were bolder or more naive about risk than their wild cousins, but they still showed a remarkable instinct for self-preservation. When they met their first-ever cat in the farmyard they immediately took refuge - suggesting an 'innate aversion' to cat odours. And the females took the precaution of storing food for pregnancy - even though they had always been fed daily. Within hours the lab rats had also adopted a 'hopping gait' characteristic of wild rats, and began to dig, something they could not do before.
Within days they began to establish a hierarchy along traditional lines. The bigger ones remained dominant once they had won an encounter, even when they were outgrown, showing that age meant something.
They also established a network of runs between key locations of food and shelter which the rats navigated by smell so effectively they did not have to look where they were going - again as they do in the wild.
'Domestic rats are now not the same as wild rats, in the same way that a dog is different from its ancestor, the wolf, but nevertheless some remnant of wolf-like behaviour is in your dog. That's the general principle,' said Berdoy.
'We're not just looking at a mass of cells; you're looking at a very sophisticated [mammal]_ rats have evolved for specific purposes. All animals will have evolved to do certain things. If you do not keep an animal properly then you are likely to get biased results because that animal is a stressed being.'
Rats and mice are popular lab animals because like humans they are successful social omnivores, which share 95 per cent of the same genes, and unlike other mammals are easier to keep because they are small, adaptable and quick to reproduce.
BErdoy is wary of taking the comparisons too far, but says modern humans who had to fend for themselves in the wild would probably resort to many of the same tactics as the rats - especially when it came to finding safe food, establishing social hierarchies, and even possibly sex.
The important social comparison was echoed by Dr James Thompson, senior lecturer in psychology at UCL in London, who said humans in comparable situations - such as disasters - could organise themselves into a useful society within hours.
'There is a massive change in priorities for action and it isn't necessarily distinctive Lord of the Flies. It's sometimes supportive, but it's generally more functional than our ordinary civilised life tends to be,' he said.
He added that there was also a 'hierarchy of utility' that appeared in disaster situations. 'Practical intelligence seems to dominate, and a certain selfishness seems to have an impact on this so people have to push to do things, and people who are too polite or waiting for others to organise things tend to be left behind.'
· Last year the number of rats in Britain overtook the number of humans, with the rodent population put at well over 60 million.
· A rat's temperature is regulated through its tail.
· The collective noun for a group of rats is a pack, a rabble or a mischief.
· In central London, you are never more than 10ft away from a rat.
· Norwegian rats can swim half a mile in open water.
· One pair of rats can shed more than a million body hairs every year.
· Because they lived in the hold and gnawed on the wood, rats would indeed have been the first to leave a sinking ship.
· Rats only require a half-inch hole to get into a building.
(Compiled by Rob Colvile)
· The 27-minute film can be seen on www.ratlife.org