Why do larger animals have longer lifespans?


Small animals like hamsters only live 2-3 years (as pets) while animals like crocodiles live on average for 30 to 40 years. Is it because their bodies age or get weaker slower because they have a larger surface area or something?

Thanks for answering

In: Biology

The logic doesn’t fully fit because some larger animals have shorter lifespans look at dog breeds

It is related broadly to resource efficiency. Larger animals need more resources (food, energy) to grow. This take more time. This means they spend more time being small (young) before growing into adulthood. This means their parents need to spend more time and their own resources taking care of their young. This means the parents cannot have many children in a short period of time. To make this all work out (ie the species to survive long term) the lives of the animal must be long. If the large species don’t have long lifespan, most parents cannot raise sufficient children, the resources to have and raise kids are wasted and the species dies out.

EDIT: left out a word.

It has to do with an evolutionary theory called K and R reproductive strategy.

Larger animals (whales, elephants, humans, etc.) tend to have fewer offspring that live longer known as the “quality over quantity” approach. This is K strategy.

Smaller animals (mice, ants, frogs, etc) tend to have far more offspring which tend to have short life spans known as the “quantity over quality” approach. This is R strategy.

At some point, organisms realized in an evolutionary sense that their only chance at survival as a species was to adopt either a K or R strategy. This is also why larger animals (K strategy) tend to stay with their mothers longer. There aren’t as many of them compared to smaller animals (R strategy) to keep the species going therefore they not only have naturally longer life spans but are also protected more in infancy when they are most vulnerable.

Another factor to consider is the activity rate of the cells. Larger animal cells are slower and less active. They produce less heat and use less energy. Even their heart rate is much slower. A smaller animal is much more active. The cells produce more heat, they use more energy and their cells hence age faster. According to a study, mammals get 1 billion heartbeats per life time. So large animals with slower heart rate spread those out, and fast animals like the shrew (800-1000 beats/min) spend it up real quick.

It has been estimated that most species of mammals will get about a billion heartbeats per lifetime. The smaller the animal, the faster their hearts beat – so will expire sooner. I don’t know about non mammals.

i would like to point out this isnt the case with all animals. certain species of turtles live for centuries and not just the large tortoises but some of the small ones too. the oldest parrot hit 114 years old. some species of jelly fish are practically immune to aging. lot of spiders and bears share the same avg lifespan.

k vs r strats in large vs small animals very loosely correlates with size. the “big fish” in the small pond might be a inch but its still the biggest fish that doesnt have to worry about predators.

Large mammal = slower metabolism & slower heart rate.

Small mammal = faster metabolism & faster heart rate.

I read an interesting tidbit from Stephen Jay Gould (in “The Panda’s Thumb, iirc) that if you look across all mammals, regardless of size, we each get approx 1 million heartbeats in our lifetime. The faster the heart rate, the shorter the lifespan.

EDIT: Goulds approximation was a billion heartbeats, not a million.