With two-thirds of the world’s population expected to live in cities by 2050, it’s important to understand how this switch to urban living might alter our genetic make-up in the long term, and what benefits and risks this could entail. So to get an idea of the ways in which big city life drives evolution, researchers have been studying the genomes of rats in New York City, revealing that the rodents have had to adapt to life in the Big Apple in much the same way as humans.
In their paper – which is available on the pre-print server bioRxiv – the study authors explain that “urban rats are so closely associated with human city dwellers” that it is therefore logical to assume that both species might develop the same genetic adaptations to help them survive in big cities. By investigating the rats’ genetic response to living in New York, the researchers hope to learn about some of the changes that may be occurring in human populations.
To conduct their research, the team lured almost 400 brown rats from the species Rattus norvegicus into traps placed around New York, using local favorites such as bacon and peanut butter (sadly, no pizza) as bait. They then sequenced the genomes of 29 of these rats, and compared them to the genomes of nine rats from rural northeast China, where the species originates.
Dozens of genes were found to have become altered in the New York population when compared to the ancestral Chinese rats, largely as a response to living in an urban environment. Many of these gene variations were associated with diet, behavior, and movement, and were found to have become fixed within the local rat population – a process known as a selective sweep.
Speaking to The Guardian, study author Arbel Harpak explained that changes to genes associated with gait and movement “might have evolved to help [rats] move more easily through sewers and pipes,” while dietary genes may have become altered to help the rodents digest whatever is on the local menu.
"In New York, you can see [rats] eat bagels and beer; in Paris, they like croissants and butter,” he explained. Given that rats tend to dine on scraps left by humans, the changes seen in genes associated with digestion may reveal what is in store for the ever-increasing number of city-dwellers around the world.
The study authors also noticed changes to a gene called CACNA1C, which modulates anxiety in rats and has been associated with psychiatric disorders in humans. This finding, they say, could open up a new route of investigation into the ways in which big city life affects our mental health, and what steps can be taken to limit the negative impact of the urban rat race on our bodies and minds.