Generally speaking, the tallest people are about 35 percent taller than the shortest ones — the difference between someone who is 6 feet 6 inches and another person who is 4 feet 9 inches. But the difference from largest to smallest in the dog world can easily exceed 400 percent. To put it another way, if people were sized like dogs, it would be nothing to see people 9 feet tall casually mingling with those 2 feet tall, with even greater differences entirely normal.
It wasn’t always that way with dogs. Originally, new research suggests, all dogs were on the smaller side, like canids such as foxes. They had a pair of gene alleles (one from each parent) that were encoded for “little.” But over time, that gene underwent a mutation that allowed for the growth of a larger animal. If a dog has matching genes to grow larger, she will grow up to be a bigger dog, and if she has one gene for “small” and the other for “large,” she will be somewhere in the middle.
The new finding turns scientists’ theories about dog size on its ear. It used to be thought that dogs started out large and became smaller as they were domesticated. Now it seems apparent that the opposite is true.
Interestingly, the current extremes in dog sizes emerged only in the last couple hundred years, when modern breeders created tiny and gigantic dogs via intentional breeding. It’s not simply one gene variation that causes all the differences. The variation in size between dogs is attributable to a number of different genetic influencers. The upshot: today’s dogs differ more in size than any other species of mammal on the planet.
