Why Don’t Big Dogs Live as Long as Small Dogs?

iStock / yellowsarah
iStock / yellowsarah

Large animals tend to live longer (sometimes much more so) than smaller ones*. A cat is going to live longer than a rat, you’re going to live longer than a cat and a Galapagos tortoise is going to live longer than you. The world’s smallest mammal, the bumblebee bat, is thought to live 5 to 10 years, while the largest, the blue whale, lives for 80 to 90. Scientists think that this happens because of the way differently-sized animals use energy. Big animals’ cells are slower and more efficient, so their parts wear out slower and last longer.

Forget about all the other animals and focus on just one species, though, and you see this trend reverse. Within a species, larger size seems to carry a longevity cost. Scientists have seen this is in mice, horses, and even humans**. The phenomenon is well known to dog lovers: Dogs from bigger breeds don’t live as long as smaller ones. The small breeds have an average life expectancy of 12 to 14 years; for larger breeds, it's 8 to 10; and for the so-called “giant breeds,” lifespan is 5 to 8 years. 

This strange flip in the relationship between size and lifespan isn’t completely understood, and many, if not all, of the factors at play are probably species-specific. This is certainly the case for dogs, and scientists think that the reasons big breeds die young have to do with the way humans have bred them and the way they grow. 

Larger dogs grow very big very fast. Take a one-year-old Great Dane, for example. It’s huge. From birth to their first birthday, they increase 100-fold in weight. In that same time frame, wolves increase 60-fold, poodles 20-fold and humans only threefold. Research in the last decade has suggested that larger individual animals die younger because this sort of accelerated growth comes with increased free-radical activity. 

A new study published last month focused only on dogs and likewise concludes that big dogs die young because they age quickly. The European researchers looked at veterinary data for 74 breeds and more than 50,000 individual dogs, including when and how they died, and found that “large dogs age at an accelerated pace, suggesting that their adult life unwinds in fast motion.”

Faster aging isn’t the only explanation, though. Larger dogs are more prone to health issues like developmental disorders, musculoskeletal and gastrointestinal diseases, and tumors—all of which are also linked to their accelerated growth and appear to be the nasty side effects of selective breeding for large size over a short (relative to the millennia other animals have had to evolve by natural selection) period of time.

There are some notable exceptions, of course, like the relatively small African grey parrot, which can live 50 to 60 years. 

Tom Samaras has been studying links between human height and other characteristics for decades. After looking at height and age of death for people in a number of historical samples, he found that shorter stature is strongly linked to longer life. Among 3200 deceased pro baseball players, for example, he worked out that every cm of height a player had over the average shortened his life by .35 years.

Why Do Bats Hang Upside Down?

iStock.com/CraigRJD
iStock.com/CraigRJD

Stefan Pociask:

The age-old question of upside down bats. Yes, it is awfully weird that there is an animal—a mammal even—that hangs upside down. Sure, some monkeys do it when they're just monkeying around. And a few other tree climbers, like margays, hang upside down if they are reaching for something or—again, like the margay cat—may actually even hunt that way ... But bats are the only animals that actually spend most of their time hanging upside down: feeding this way, raising their young this way, and, yes, sleeping or roosting this way.

There is actually a very good and sensible reason why they do this: They have to hang upside down so that they can fly.

First off, we have to acknowledge that bats are not birds, nor are they insects. These are the other two animals that have true powered flight (as opposed to gliding). The difference between bat flight and bird or insect flight is weight—specifically, the ratio of weight to lift-capacity of the wings. If you walk up to a bird or insect, most species will be able to fly right up into the air from a motionless position, and do it quickly.

Bats, on the other hand (or, other wing), can’t do that. They have a lot of difficulty taking off from the ground (not that they can’t do it ... it’s just more difficult). Insects and birds often actually jump into the air to give them a start in the right direction, then their powerful wings take them up, up, and away.

Birds have hollow bones; bats don’t. Insects are made of lightweight chitin or soft, light tissue; bats aren’t. And bats don’t have what you could call "powerful" wings. These amazing creatures are mammals, after all. The only flying mammals. Nature found a way to evolve such an unlikely thing as a flying mammal, so some compromises had to be made. Bats, once airborne, manage perfectly well in the air, and can literally fly circles around most birds in flight. The problem is in first getting off the ground.

To compensate for the extra weight that mammals must have, to compensate for the problem of getting off the ground, evolution found another way for bats to transition from being motionless to immediately being able to fly when necessary. Evolution said, “How about if we drop them from above? That way they are immediately in the air, and all they need to do is start flapping."

It was a great idea, as it turns out. Except bat feet aren’t any good for perching on a branch. They are mammals, not birds, so their musculature, their bones, and their tendons are set up in a completely different way. When a bird squats down on a branch, their tendons actually lock their toes into an even tighter grip on the perch. It happens automatically. That’s part of being a bird, and is universal. That’s why they don’t fall off in their sleep.

Bats, as mammals, are set up differently. Therefore, to compensate for that fact, nature said, “How about if we have them hang upside down? That way, their tendons will actually pull their toes closed, just like a bird does from the opposite direction.” So that’s what evolved. Bats hang from the bottom of something, and all they have to do is "let go" and they are instantly flying. In fact, with this gravity-assist method, they can achieve instant flight even faster than birds, who have to work against gravity.

Side note: In case you were wondering how bats poop and pee while upside down ... First off, pooping is no big deal. Bat poop looks like tiny grains of rice; if they are hanging, it just falls to the floor of the bat cave as guano. Pee, however ... well, they have that covered too. They just “hold it” until they are flying.

So there you go. Bats sleep hanging upside down because they are mammals and can’t take off into the air like birds can (at least not without difficulty). But, if they're hanging, all they do is let go.

Makes total sense, right?

Now, having said all that about upside down bats, I must mention the following: Not all of the 1240-plus species of bats do hang upside down. There are exceptions—about six of them, within two different families. One is in South America (Thyropteridae) and the other is in Madagascar (Myzopodidae). The Myzopodidae, which includes just one species, is exceedingly rare.

So it turns out that these bats roost inside the tubes of young, unfurled banana leaves and other similar large leaves. When they attach themselves to the inside of this rolled leaf, they do it head-up. The problem with living inside of rolled-up leaves is that within a few days, these leaves will continue growing, and eventually open up. Whenever that happens, the whole group of bats has to pick up and move to another home. Over and over again. All six of these species of rare bats have a suction cup on each wrist and ankle, and they use these to attach to the smooth surface of the inside of the leaf tube. Evolution: the more you learn, the more amazing it becomes.

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

Sorry, But Last Month's Polar Vortex Didn't Wipe Out 95 Percent of Stink Bugs

iStock.com/drnadig
iStock.com/drnadig

In the wake of the polar vortex that brought bone-chilling temperatures to the Midwest and Northeast U.S. last month, a silver lining appeared to emerge. Multiple media outlets recently reported that the weather phenomenon may have wiped out as many as 95 percent of brown marmorated stink bugs in areas that weren't accustomed to such frigid conditions.

Unless you like having your home smell like the musky, burnt-cilantro scent of squished stink bugs, we have some bad news: Those reports are not entirely accurate. According to KDKA Radio in Pittsburgh, the Virginia Tech lab experiment that has been widely cited in these articles is a little outdated, having been conducted in 2014.

At the time, it appeared to be a promising find. Researchers from the university had collected stink bugs, placed them in insulated buckets, and waited to see if they'd survive a particularly cold spell. Even though the insects were in a dormant state called diapause, 95 percent of them died when a polar vortex hit the region. That led entomology professor Thomas Kuhar to tell The Washington Post in 2014 that “there should be significant mortality of BMSB (brown marmorated stink bugs) and many other overwinter insects this year."

However, in an email to Mental Floss, Kuhar says the rehashing of "some media misquotes from 2014" led to these too-good-to-be-true reports being recirculated this week. "There is no new research on this topic," he writes. Furthermore, the lab experiment can't easily be applied to real-life scenarios because stink bugs tend to seek shelter during the winter. "Severe sub-freezing temperatures will negatively impact winter survival of these stink bugs if they were unable to find suitable shelter such as inside of houses and sheds," he writes.

These sentiments were echoed by entomologist Chad Gore of Ehrlich Pest Control, who spoke with KDKA Radio. "When they can find that shelter, they can survive the winter. Those that are exposed, they will freeze and we won’t have to worry about them," he said.

But is there still a chance we will see fewer stink bugs in the spring? Gore says don't count on it. "I’d love to be able to reassure everybody and say that 95 percent of all of our stink bugs are going to be gone, but that’s just not going to be the case," he said. "We’re still going to see them."

Even though stink bugs don't bite and are basically harmless (though they sometimes trigger allergic reactions), they can be difficult to trap once they've found a way into one's house. The invasive species is also harmful to crops—especially grapes—and sometimes end up getting pulverized and fermented in red wine. Suffice it to say, a lot of people would be happy if the pests suddenly disappeared. For now, though, we'll have to keep on dreaming.

[h/t KDKA Radio]

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