How come smaller dogs generally havw longer life spans than larger dogs, but larger animals, like horses, have an even longer lifespan?
In: Biology
a key difference is that horses and dogs are completely different species; so completely different set of expectations
a chihuahua and a great dane are the same species, despite their visual differences……
being big can be hard on the body; tall people and overweight people tend to die earlier than shorter and leaner people.
so smaller dogs live longer cause their metabolism is faster and they age slower compared to big dogs but horses are just built different they chill a lot and eat grass. guess being a horse is a pretty sweet life
There is a rule of thumb that smaller animals have shorter lives and bigger animals have longer lives (though it has many exceptions, like parrots and humans). But breeds of dog are all the same species we have made different through rapid selective breeding, and when you breed them to be very large they burn way more calories than their metabolism “expects” and build up damage quickly.
Most mammals hearts beat the same number of times before you die approximately 1.5 Billion.
Smaller animals hearts beat faster and larger animals beat slower.
There’s a bit more too it and there are obviously exceptions and some animals like jelly fish don’t even have hearts.
Within the same species like dogs for example a larger heart might pump less frequently but they have increases the risk of diseases and arthritis and cancer and more strain on their hearts that make them live significantly shorter lives on average.
The longest living dogs ever are not the smallest dogs breads but actually smallish-medium size dogs.
Portuguese Rafeiro do Alentejo breed has the record for longest living dog at 30 years and they average 35-40kg.
If you look within a species most animals will have a bell curve where being about average size provides the longest natural life expectancy but across species larger animals with slower beating hearts generally live longer.
It all comes down to genetics.
Within the human species, the same issue occurs where larger and taller people are more likely to die earlier (primarily from cancer).
We only vaguely understand what determines lifespan. We’ve got some theories but none of them are sophisticated enough yet that we could, say, analyze an unknown species and accurately guess its lifespan.
But what we do know is it has to do with the genetic code that defines a species. Some animals have tougher organs that can go longer without aging. Other animals have DNA that’s more resilient to accidental errors during copying. There are a handful of factors like that that contribute to lifespan.
In dogs’ cases, while there are dozens of breeds they all descended from the same common ancestor and they share a lot of genetic similarities. So in general, most breeds have a heart that is just as “tough” as any other dog breed. That’s why larger dogs tend to die quicker: a bigger body works the heart more so they “wear out” faster. It’s also notable here that dogs are a HIGHLY domesticated animal, for the past few thousand years we have purposefully accelerated their evolution towards dozens of different “working breeds” and sometimes “long lifespan” wasn’t something the breeders cared about. Some of the smaller breeds have intentional birth defects that can significantly shorten their lifespans!
But while horses and dogs do have some common mammalian ancestor somewhere, it’s much more distant so their genetics are very different. Horses have a much “tougher” heart and other organs. So they handle being a larger creature with a longer life. We haven’t tinkered with horses through breeding quite as extensively as we have with dogs.
Put another way: If the “ancestral dog” is like a Honda Civic, all of the breeds are like people’s aftermarket tinkering. Some people make sporty models, but those parts tend to have a short lifespan. Other people focus on reliability and make a car that lasts even longer than the original.
But horses are like a Kenworth truck cab. They are similar to cars and have similar parts, but everything was built to haul much more weight and be very reliable for long trips. There’s not quite so much diversity among different kinds of trucks like this.
Other animals are like space shuttles, and wagons, and trains, etc. They’re all built out of such different parts it creates completely different lifespans. Nature isn’t always optimizing for longer life.
yo it’s wild how that works right smaller dogs live long because they don’t wear out as quick like a tiny engine running smooth. but for big animals like horses it’s more about their biology and care they get. life’s complicated but nature’s pretty cool
It’s the same with humans. Taller people are expected to have shorter lifespans than short people. Simply put, because there is more of them to go wrong. Think how many cells there are in a person. A tall person obviously has more cells. More cells = more chance of something going wrong within one of them to cause diseases like cancer and the more of you there is, the more your heart has to work to get blood everywhere, more blood is required to fill your body, your lungs work harder to oxygenate all that blood, you kidneys and liver work more filtering it.
The more of you there is, the more strain you put on your body, which is also why obese people have shorter life spanss.
Same thing applies to dogs. Even though they’re different breeds, they’re the same species. So, within their species, big dogs are more likely to die sooner than small dogs.
Remember though, that only applies within a species.
Outside of species, when comparing different species, it’s actually larger animals that tend to live longer. This is due to a lot of factors, but one main one being, the smaller an animal is, the more likely it is to be prey. Which means they need to breed fast before being eaten. The result of breeding fast, is they don’t need to live long, just long enough to reproduce. On the reverse, the bigger an animal is, the less likely it is to be prey.
So a general rule is, smaller animals evolved to have short lives and breed quickly, where as bigger animals evolved to live longer and therefore can breed more slowly.
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