Dog Size And Lifespan: When Bigger Isn’t Better

By Jon Bastian

Dog lovers have no doubt noticed that smaller dogs live longer than large ones, and now there’s a scientific study to back that up, as well as a few hypothesis as to why this is true.

When compared to the lifespan of other mammals, “smaller size, longer life” would at first glance appear to be counter-intuitive, especially to families that have gone through short-lived pet rats (2 years), hamsters (3 years), or gerbils (4 years).

In the non-pet category, chimpanzees live shorter lives than humans — about 45 years vs. 70 years — and elephants have a lifespan comparable to humans. This is nothing, of course, compared to the bowhead whale. Weighing in at up to 65 tons and sixty feet long, current estimates place its maximum lifespan at 200 years.

Following this logic, then, we should expect a Great Dane to live longer than a Chihuahua, but that’s not the case. The former only live, on average, 6 or 8 years, while the latter can live up to 18 years.

As it turns out, while bigger species of mammals live longer than smaller ones, within species it’s reversed. While the following example may be anecdotal, it does indicate that even humans are subject to this rule; Wilt Chamberlain, the professional basketball player, was 7’1” tall and died at 63. Jerry Maren, the 4’3” actor best known as one of the Lollipop kids in the 1939 version of “The Wizard of Oz,” is still alive at 93.

The effect is even more pronounced in dogs, which have a more extreme range of sizes. According to the Guinness Book of World Records, the largest dog, a Great Dane named Zeus, was about as big as Wilt Chamberlain, measuring 7’ 4” feet in length and weighing 155 pounds. The smallest living dog is a Chihuahua named BooBoo, at 4 inches tall and 1.5 pounds.

For comparison, applying that size difference to the shortest verified human, 21 inch tall Chandra Bahadur Dangi, would give us a tallest human at about 31’ 5”. Going in the other direction, with 8’ 11” Robert Wadlow as the tallest human, the same size ratio would make the shortest human just barely under 6 inches tall. Incidentally, Chandra is still alive at 73, while Wadlow was only 22 when he died.

Recently, scientists tried to determine why this is the case. In a study led by Dr. Cornelia Kraus, a research scientist and lecturer at the University of Göttingen in Germany, researchers analyzed data on age of death in over 56,000 dogs from 74 different breeds, and were able to put a number on it. They found that, for every increase of 4.4 pounds of body weight, a dog’s lifespan decreased by 1 month.

The next step will be to determine why larger dogs live shorter lives, but the scientists already have some ideas. At its simplest, larger dogs die younger because they age more quickly. They age more quickly because they grow faster. This can lead to earlier incidence of tumors and other abnormal tissue developments, including cancer. It can also contribute to abnormal development, leading to physical conditions impacting health.

Dr. Kraus’s study, “The size-lifespan trade-off decomposed: Why large dogs die young,” will be published soon in The American Naturist.

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