The great adaptability of the brown rat manifests itself in its genes.
According to the growing crowd of Donald Trumps among us, much of the misery afflicting modern humans comes from China. The brown rat actually comes from China, but humans themselves are largely responsible for its success. He took care of the transport of the rat: the animals traveled as stowaways on ships. Subsequently, the rats were found to flourish in less hygienic living conditions, further contributing to their success by the polluting and wasteful humans.
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According to the growing crowd of Donald Trumps among us, much of the misery afflicting modern humans comes from China. The brown rat actually comes from China, but humans themselves are largely responsible for its success. He took care of the transport of the rat: the animals traveled as stowaways on ships. Subsequently, the rats were found to flourish in less hygienic living conditions, further contributing to their success by the polluting and wasteful humans. Brown rats arrived in Europe during the 16th century, from where they would conquer Africa and America. It was not until the 18th century that they would reach North America, again accompanied by travellers. Rats in New York City, research reported by Nature, have developed substantial genome differences compared to the animals from the original population in northeast China. New York’s rats have adapted to the urban jungle that has become their habitat, with changes in dozens of genes affecting behavior, nutrition and movement. The city rat seems to have become a different rat from the country rat – originally the rats were animals of open grasslands, where they lived mainly on plant material. The brown rat is so successful that it is impossible to make reliable estimates of its population size. There are quips circulating like: ‘Everywhere you go, there’s a rat within ten meters’ (in cities, even within two meters). The truth is that the numbers vary so much that no one knows how many there are. It’s also not that important: brown rats are ubiquitous, but their numbers depend a lot on local conditions. They are much more common in sewers and on farms than in residential areas or open landscapes. Brown rats can become impressive beasts, up to 30 centimeters in length with a tail of another 25 centimeters. They seem to be living in a permanent rat race: their heart rate is more than 300 beats per minute by default and they breathe more than 100 times per minute. They can handle great distances and sometimes roam miles in search of a better or safer home. But if they get it right, they can live for months without moving more than 20 meters. The reproductive capacity of brown rats is also impressive. A female can handle five litters of seven young on average each year. She is only 21 days pregnant each time. Things are moving forward in the rat world. The lifespan of the average brown rat is limited to one year – three years is the maximum. It’s a high-turnover community. An intriguing study appeared in Science Advances illustrating that rats have things in common with humans. They appear to suffer from the so-called ‘bystander effect’, which means that people will not help others in need if they notice that other passers-by (also) are not doing anything. This also applies to rats that have to help an animal that has become trapped. If other rats don’t do anything, chances are no rat will come to the rescue. But if one takes an initiative, the others also take action. Being social can be contagious.
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