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Why Do Small Dogs Live Longer Than Large Dogs?

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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.

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Big Questions
What Is the Difference Between Generic and Name Brand Ibuprofen?
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What is the difference between generic ibuprofen vs. name brands?

Yali Friedman:

I just published a paper that answers this question: Are Generic Drugs Less Safe than their Branded Equivalents?

Here’s the tl;dr version:

Generic drugs are versions of drugs made by companies other than the company which originally developed the drug.

To gain FDA approval, a generic drug must:

  • Contain the same active ingredients as the innovator drug (inactive ingredients may vary)
  • Be identical in strength, dosage form, and route of administration
  • Have the same use indications
  • Be bioequivalent
  • Meet the same batch requirements for identity, strength, purity, and quality
  • Be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products

I hope you found this answer useful. Feel free to reach out at www.thinkbiotech.com. For more on generic drugs, you can see our resources and whitepapers at Pharmaceutical strategic guidance and whitepapers

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

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

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