Why Do Small Dogs Live Longer Than Large Dogs?

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iStock

Why do small dogs live longer than large dogs?

Adriana Heguy:

The issue of body size and lifespan is a fascinating topic in biology. It’s strange that across species, at least in mammals, large-bodied animals live longer than small-sized animals. For example, elephants live a lot longer than mice. The theory is that
bigger animals have slower metabolisms than small animals, and that faster metabolisms result in more accumulation of free radicals that damage tissue and DNA. But this doesn't always hold for all animals and the “rate of living” theory is not widely accepted. What we cannot clearly understand remains fascinating.

But now if we look at within a given species, lifespan and body size are inversely correlated. This is definitively the case for dogs and mice, and it has been proposed that this is the case for humans, too. Why would this be? A possible explanation is that larger dogs (or mice, or people) grow faster than their smaller counterparts because they reach a larger size in more or less the same time, and that faster growth could be correlated with higher cancer rates.

We do not have a clear understanding of why growing faster leads to accelerated aging. But it seems that it is an accelerated rate of aging, or senescence, that causes larger dogs to have shorter lifespans than little dogs.

The figure above is from Ageing: It’s a Dog’s Life. The data is from 32 breeds. Note that the inverse correlation is pretty good, however some large dog breeds, at around 40 to 50 kg (or about 88 to 110 pounds), live 12 or 13 years in average while some other dog breeds of equal body size live only eight or nine years on average. This is due to dogs being a special case, as they were artificially bred by humans to select for looks or behavior and not necessarily health, and that considerable inbreeding was necessary to produce “purebred” dogs. For example, boxers are big dogs, but their higher cancer rates may result in a shorter lifespan. However, the really giant breeds all consistently live eight to nine years on average. So there is something going on besides simple breeding quirks that led to bad genetics and ill health. Something more general.

A few years ago, a large study [PDF] was published using mortality data from thousands of dogs across 74 breeds, testing three hypotheses: Large dogs may die younger than small dogs because of (1) an earlier onset of senescence, (2) a higher minimum mortality hazard, or (3) an increased rate of aging. The conclusion from their study is that aging starts more or less at the same age in small and large breeds, but large breeds age faster. We do not have a clear understanding of the underlying mechanism for faster aging in dogs. It seems that when we selected for large body size, we selected for faster aging as well. But we do not know all the genetic components of this. We know that there are at least three genes that determine large body size in dogs: IRS4 and IGSF1, involved in thyroid hormone pathways which affect growth, and ACSL4, involved in muscle growth, and back fat thickness.

But how this accelerates aging is still speculation. More studies are needed, but dogs seem to be a great model to study the evolution of body size and its relationship to aging.

This post originally appeared on Quora. Click here to view.

Why Are We So Scared of Clowns?

Warner Bros.
Warner Bros.

With the recent box office-smashing success of Stephen King's It, it’s safe to say that coulrophobia (fear of clowns) isn’t a fringe phenomenon. The colorful circus performers are right up there with vampires and werewolves on the list of iconic horror villains. But unlike other movie monsters, clowns were originally meant to make kids laugh, not hide under their beds in terror. So what is it about clowns that taps into our deepest fears?

According to Yale doctoral candidate Danielle Bainbridge, the unsettling clown stereotype goes back centuries. In the inaugural episode of the PBS digital series Origin of Everything, Bainbridge explained the long history of this pervasive part of our culture.

Before clowns wore floppy shoes and threw pies at each other’s faces, early versions of the performers could be found in royal courts. The court jester wasn’t evil, but he was the only person in the kingdom who could poke fun at the monarch without fear of (literally) losing his head. The fact that fools didn’t fall within the normal social hierarchy may have contributed to the future role clowns would play as untrustworthy outsiders.

From the medieval era, clowns evolved into the harlequins of 16th-century Italian theater. Again, these weren’t bloodthirsty monsters, but they weren’t exactly kid-friendly either. The characters were often mischievous and morally bankrupt, and their strange costumes and masks only added to the creepy vibes they gave off.

Fast-forward to the 19th century, when the white-faced circus clowns we know today started gaining popularity. Unlike the jesters and harlequins that came before them, these clowns performed primarily for children and maintained a wholesome image. But as pop culture in the 1970s, '80s, and '90s showed us, that old perception we had of clowns as nefarious troublemakers never really went away. Steven King’s It, the cult classic Killer Clowns From Outer Space (1988), and that scene from Poltergeist (1982) all combined these original fears with the more modern association of clowns with children. That formula gave us one of the most frightening figures in horror media today.

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Why Do We Call a Leg Cramp a Charley Horse?

iStock.com/Jan-Otto
iStock.com/Jan-Otto

If you’re unlucky enough to have experienced a charley horse—a painful muscle spasm or cramp in your leg—then you may have found yourself wondering what this nonsensical phrase even means. Who is this Charley character? Where did he come from? And what does he know about my pain?

Like the words flaky and jazz, this term likely entered the language from the baseball field. While the idiom’s etymology isn’t 100 percent certain, archived newspaper articles suggest it was coined by a baseball player in the 1880s. We just don’t know which player said it first, or why.

According to a January 1887 article in the Democrat and Chronicle, the phrase was well-known to baseball players at the time—but to the average person, charley horses were as enigmatic as “an Egyptian hieroglyphic.” That year, charley horses were mentioned in a slew of newspapers across America, and some attempted to tackle the phrase’s murky origin. “Nearly every sporting journal gives a different version as to how the term charley horse originated in baseball circles,” the Oakland Daily Evening Tribune reported at the time.

The likeliest tale, according to the paper, centered around John Wesley "Jack" Glasscock, a shortstop who at the time was playing for Indianapolis. At some point a few years earlier, the player had strained a tendon in his thigh during a game and afterwards went home to his farm, where his father looked after a lame old horse called a "Charley horse." When the senior Glasscock saw his son limping along, he reportedly exclaimed, “Why, John, my boy, what is the matter; you go just like the old Charley horse?” John supposedly shared the funny turn of phrase with his teammates, and from there it spread. Similar accounts were reported in other newspapers, but they were attributed to various other players.

Other reports say the phrase has nothing to do with a live animal, but rather the fact that an injured player, while running, resembles a rocking horse or a child riding astride a wooden hobby horse.

The New Dickson Baseball Dictionary by Paul Dickson details a few other theories. In two versions of the same basic tale, Orioles or Chicago Cubs players went to the races and bet on a horse named Charlie who "pulled up lame in the final stretch." The next day, a player pulled a tendon in his leg and was said to resemble “our old Charlie horse.”

Alternatively, its origin may relate to an old workhorse that was tasked with pulling a roller across the infield. “Often in the 1800s, old workhorses kept on the grounds of ballparks were called Charley. The movements of the injured, stiff-legged ballplayers were likened to the labored plodding of these old horses, and the injury itself eventually became known as a ‘charley’ or ‘charley horse,'" Tim Considine wrote in 1982's The Language of Sport.

It also appears that charley horse originally implied a much more serious injury—or perhaps there was a bit of hysteria surrounding a condition that seemed new and scary in the late 19th century. The Democrat and Chronicle described a charley horse as a “giving way of one of the small tendons of the leg” and said an injured baseball player might need an entire season to recover. Another article from 1887 said ballplayer George Van Haltren’s relatives were worried he would get a charley horse, “although they do not know what that is.” He was said to have been “very fortunate” because he had “not yet encountered the terrible charley horse.”

For comparison, Healthline.com now says charley horses “are generally treatable at home” by stretching, massaging, or icing the afflicted area, although the muscle pain can linger for up to a day in some cases. So there you have it. We may never know the exact etymology of the charley horse, but the next time you get a sharp pain in your leg, you can thank an old-timey ballplayer for making your struggle sound so silly.

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