Outside the polar ice caps, the only place in the world where you won’t find any brown rats (Rattus norvegicus) is the province of Alberta in Canada. From its home base in Mongolia, the brown rat followed the spread of human cities across the steppes, finally swimming the Volga into western Europe in 1727. From there it travelled the world on ships, scurrying ashore at every port and eventually reaching Alberta’s eastern border in 1942. The Albertans decided to fight and set up a 400-mile-long buffer zone that is still patrolled by rat vigilantes. Alberta is cold and human habitation is sparse, so they may just hang on. For the rest of us, the battle was lost before it began. In the USA there are an estimated 150 million brown rats; in the UK, they now outnumber the people.
Here’s the problem. A rat can swim for 72 hours non-stop. It can jump down 50 feet without injury. It can squeeze through a half-inch gap, leap three feet, climb vertical surfaces and walk along ropes. It can survive longer than a camel without water. It will eat anything that’s edible and lots of thing that aren’t (lead sheeting, soft concrete, brick, wood and aluminum). It reaches sexual maturity at three months. An on-heat female can have sex over 500 times with a barnload of different males and produce 12 litters of 22 young each year. In short, rats are very, very hard to get rid of.
The trouble with the rat-race is that even if you win, you're still a rat.
Dr Jaak Panksepp, an Estonian-American neuroscientist and psychologist, found that tickling rats produces chirping noises which he says may be laughter. The sounds are too high-pitched for the human ear - but can be clearly heard if recorded on special equipment. The rats definitely enjoy being tickled – they actively seek out the hands of people who have done it to them before.
Dr Panksepp hasn’t managed to prove rats have a sense of humour, but he says that young rats have a ‘marvellous sense of fun’ and thinks they probably like slapstick. They also chirp when wrestling, mating and about to be injected with morphine. It’s claimed that dogs and chimpanzees laugh too (although it sounds rather like panting).
Dr Panksepp is also known for an interesting piece of research where he found that rats given a cat hair show fear, even if they’ve never been anywhere near a cat before.
In the winter, many people suffer from Seasonal Affective Disorder (SAD). It seems rats get it too – but in the summer. Researchers at the University of California, San Diego took two groups of rats. Each day for a week they exposed one group to five hours of light and 19 hours of darkness and the other to 19 hours of light and five of darkness. They found that the rats that spent most of the week in the dark generated more of the pleasure hormone dopamine, while the rats kept in the light made more somatostatin, which is linked to anxiety. The ‘winter’ rats were more self-confident and the ‘summer’ rats more stressed.
Four million years ago, rats in South America were the size of hippos.
Rats can't vomit.
Behavioural psychology is the science of pulling habits out of rats.