Why do smaller dogs live longer than bigger breeds?

Chris asks Sarah Harrison from the University of Cambridgewhy smaller dogs live longer than bigger breeds?

Sarah - Absolutely it’s the case. I think that’s why this makes a great question because, as Michael says, larger mammals tend to live longer, so elephants tend to live a really, really long time. But when you look within species, the trends almost reversed and this is why, as Michael points out for dogs, if you are a larger dog, you tend to have a shorter lifespan than a smaller dog.

It’s not just dogs, this trend holds in humans as well. The tallest every human that’s ever been recorded to have lived was about 8 ft. 11, but this poor chap died at 22 years old so being large didn’t gift this poor guy with longevity.

Chris - Those people are obviously a little bit exceptional aren’t they because something made them become extraordinary big compared to the norm, but going back to the original question about dog size,what is the reason why a bigger breed will be outlasted by a smaller breed?

Sarah - We don’t know the full answer to this and we think the reason behind this is because larger animals grow a bit faster. This means they’ve got a higher resting metabolic rate so they’re exposed to more reactive oxygen species that can lead to DNA damage. The other thing is these animals have a lot more cells in each of their organs which means more cells have a higher chance of getting some kind of somatic mutation that might lead to cancer or tumour regenesis. But, as I say, the full answer is not known.