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NEW YORK — It sounds more like a real estate issue than a scientific one, but the difference between a downtown Manhattan neighborhood and an uptown one can be discerned by the rats that live there. That’s the conclusion of a new study by researchers at Fordham University after two years of detailed genetic analysis. Their discovery that uptown rats and downtown ones are genetically different could ultimately make life in cities — no matter what the neighborhood — better.

“Rats uptown and downtown don’t share as many relatives,” said Matthew Combs. He’s a PhD candidate at Fordham, who, under the direction of Prof. Jason Munshi-South, has carried out DNA analysis on more than 200 Manhattan rats over the last two years.

Combs said that at different ends of the island, rat populations breed among their closest colonies, making it difficult “to make the jump between uptown and downtown.”

In other words, Combs said, rats below 14th Street in Manhattan are different from rats above 59th Street, due to generations of rats breeding relatively close to home. The average life span of a brown rat, like those that live in New York City, is two years, meaning that isolated breeding has gone on for hundreds of generations, since rats arrived in Manhattan on board Dutch and British ships, when New York was still a colony of those countries.

The reason for the relatively isolated breeding, Combs’s research shows, is that there are far fewer human homes — and therefore less food garbage that rats rely on, as well as fewer places to burrow — in Manhattan’s mid-section.

“In Midtown there are fewer rats,” Combs said, with “fewer places they can live, which leads to a differentiation in these uptown and downtown groups.”

It is pioneering research, achieved by Combs and a team of undergraduates trapping rats, and cutting off a one-inch section of tail of each one, before releasing them. The tail sections are then analyzed genetically, and that analysis has found different genetic mutations between rats living in the northern half of Manhattan island and its lower one-fifth.

“What difference does it make?” asked Larry Riggs, a downtown Manhattan resident and skeptical New Yorker.

The answer might lower his, and other New Yorkers’, skepticism, at least somewhat.

“Rats obviously carry a host of deadly pathogens,” Combs pointed out. “They’re a public health threat. So we’re hoping the work we do can help inform better management strategies, and can lead to a more efficient reduction in rats.”

The Fordham research can be seminal in helping to fight rat infestations in New York City and elsewhere. The study’s results will be shared with, and compared to, related analyses in other cities with large rat populations in the U.S., Canada and Brazil.

It leaves New Yorkers like Rich De Simone optimistic, but cautiously so.

“Are they going to eradicate all the rats?” De Simone asked. “No, but they can certainly reduce the number of rats we have in the city. No question about it.”