Humans and rats have more in common than you may think – that’s according to a new study which suggests they have undergone parallel shifts in their genetic make-up in response to city life.
Scientists who analysed 29 brown rats from New York, suggest they – and us – are now more prone to similar health threats relating to pollution and the consumption of sugary foods.
The researchers – lead by Columbia University population geneticist Arbel Harpak – wanted to find out whether or not the animals were changing genetically as they adapted to modern life.
To do so, they lured the New York rats into traps with bacon, peanut butter and oats, and compared their genomes with those of nine brown rats from Heilongjiang, northeast China – where the species originated.
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They found several dozen rat genes that had shown major changes in DNA over hundreds of years as the species moved across Asia and into Europe, and to the US.
The altered genes are related to diet, behaviour and movement, and reflect the need for the animals to adapt in order to live alongside humans in cities, according to the study published on the bioRxiv website.
One of the genes highlighted has been linked to location behaviour and could reflect how rats today have to move through artificial environments, meaning they could have evolved to move through sewers and pipes more easily.
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“The gait or other locomotory phenotypes could have also undergone adaptive changes, given that urban rats must move through a highly artificial, constructed environment that differs markedly from naturally vegetated habitats,” the researchers wrote.
They say the city-dwelling rats are so closely linked with their human counterparts that it is possible that similar genetic changes have occurred in both species.
“Humans and other animals have shown convergent adaptation to a change in environment in other cases, such as the move to high-altitude habitats,” they explain.
“Exposure to diseases such as tuberculosis in ancient cities promoted the evolution of resistance in urban humans.
“Like humans, rats likely live in higher densities in cities, leading to increased pathogen transmission potential and load. In addition, mosquito species that have rapidly invaded urban areas across the world feed on both rats and humans, suggesting a novel, shared disease exposure in cities.”
The study said the “most striking” commonality between brown rats and humans was their diets.
They wrote: “Previously, humans have been shown to exhibit adaptations associated with shifts from hunter-gatherer to agricultural societies.
“Today, the human urban diet contains an increasingly large proportion of highly processed sugars and fats that lead to a number of public health concerns. Some of these health concerns could conceivably apply to rats as well.”