Why Do Animals Have Short Lifespans? (Explained)

Why Do Animals Have Short Lifespans
Fact Checked and Reviewed by: Mark Rhodes, Ph.D. - Wildlife Biologist
Dr. Mark Rhodes holds an MS in Fisheries and Wildlife along with a Ph.D. in Wildlife Ecology. He helps maintain our editorial standards of accuracy and quality. You can read more about Dr. Rhodes here.

Pets don’t live as long as people. It can be sad to think that your furry friend (or scaled friend in the case of fish and reptiles) isn’t going to be with you for the long haul. But, it’s a sad reality that we often will outlive our pets.

This is also true for many animals in the wild. Tigers, lions, bears, gorillas, elephants, birds, and so many small mammals all have shorter lifespans than humans. In fact, with the exception of marine mammals, humans are the longest-living mammal.

So, why do animals have short lifespans?

Animals have shorter lifespans than humans for several reasons. In the wild, animals face challenges that might cut their life short. Domesticated pets and animals in captivity don’t have these same challenges but may age faster because of the number of neurons in their brain and how fast their metabolism ages them. 

Below, we’ll take a look at what exactly aging is and why animals age faster than humans. I’ll also talk a little about the lifespans of different animals as we go along and the differences in the life expectancy of animals in captivity vs. animals in the wild.

What Exactly Is Aging?

Before we can get into why animals age faster than humans, let’s talk a little about what aging is. Yes, the age of something is the number of years that it has been alive. But did you know that aging causes changes on a biological level?

When you are an infant and grow into an adult, your cells are still growing and multiplying. They are generally healthy. As a person reaches middle age, though, their body experiences changes on a cellular level.

As cell membranes change, they may not distribute oxygen and nutrients to your cells as they once did. They also may struggle to remove carbon dioxide and waste as efficiently, which accumulates in your body. Connective tissues also get stiffer, making airways, blood vessels, and organs stiffer and less resilient.

So yes, aging is a number of years. But it’s also a biological process that describes the decline that people experience in middle and late age. In people who die from aging rather than disease, it happens because their body eventually stops working as cells slow down and eventually stop functioning.

Why Do Animals Age Faster Than Humans?

One theory on why animals age faster than humans is that larger animals have a slower metabolism, which makes an animal like an elephant age at a much slower rate than something like a shrew or weasel. This lower metabolic rate means that cells don’t age quite as fast.

While bigger animals do expend more energy, they have more tissue and cells that go through the aging process than smaller animals. It’s also known that regardless of species, a gram of tissue expends a certain amount of energy before dying completely, which is the reason it was hypothesized bigger animals live longer.

A second theory, one that has proven more accurate in predicting animal lifespans, is that animals with more neurons live longer. One good example of this is gorillas, some of which are the same size (if not bigger than) humans when standing erect. They have a life expectancy of just 35 years compared to a human’s average lifespan of 75-90 years depending on the country they live in.

That being said, it’s worth noting that humans aren’t the only animal that lives a long time. Bowhead whales, for example, are known for living as long as 200 years. Some non-mammals also have long lifespans. The Galapagos Giant Tortoise generally lives to be over 100 years old, while Greenland sharks are known to live 300-500 years.

In this video, you can meet 190-year-old Jonathan, perhaps the world’s oldest land animal:

Why Do Different Animals Have Different Lifespans?

While it was once believed that animals had different lifespans based on their body size and metabolism, one study also identified the number of neurons in an animal’s brain as being linked to their rate of aging. This may have something to do with the significant role that the brain plays in the body.

When you look at animal aging and how size and metabolism play a role, there is only about 20-30% accuracy that predicts animal aging based on size. There are also outliers, such as in the case of birds. Birds live about 10 times as long as mammals that are the same size.

That being said, when using the number of neurons in the cerebral cortex to predict aging in animals, there was about 70-80% accuracy. This isn’t 100% accurate, but it is a much better, more accurate picture of animal aging than animal size offers.

Something to note is that size might also play a role in the longevity of animals within a specific species. When there is fighting or competition among members of a species, the larger animal is more likely to survive. However, this situation only applies to deaths that happen in the wild and not naturally occurring animal deaths.

Why Do Animals Have Short Lifespans In The Wild?

In addition to the reasons mentioned above, animals have short lifespans in the wild because there are more threats to their longevity. Animals in the wild have to deal with competition from other members of their species and threats from hunters and poachers. Overexploitation, which happens when a species is hunted too much, is another challenge animals face.

There are also other risk factors like exposure to pollution, habitat loss that may cause a species to become endangered, invasive species in the area, loss of natural food sources, and any other number of challenges that may arise. Disease introduced by humans or other animals also puts critters in the wild at risk.

Plus, the world that we live in is constantly changing from human development. Those species that cannot keep up with or adapt to these changes fast enough may also perish.

Furthermore, these wild animals do not have access to medical care like animals kept in captivity do. This means that if they are injured or fall ill, they may not be able to recover and may perish as a result.

How Do Scientists Know The Age Of Animals In The Wild?

The way that scientists know the age of animals in the wild changes based on the individual animal. Fish, for example, have growth rings formed in the scales that can tell how many winters have passed. This is most accurate in the north, where winters are harsher, and it has to do with an animal’s growth pattern in relation to the seasonal changes.

For animals like goats and sheep, by contrast, researchers can identify information by looking at the development of their teeth. The same is true of elephants, who have multiple sets of teeth. Researchers can tell which set of teeth they are on and use that information to predict age.

Of course, researchers also tag some animals in the wild and track information about their movements, patterns, and age. This doesn’t hurt the animal and it provides a lot of useful information for different purposes.

Why Do Animals Live Longer in Captivity?

Animals live longer in captivity for two basic reasons. First, animals in captivity live without the same dangers they’d have in the wild. They don’t have to live in fear of their natural predators every day. There also isn’t the risk of poachers, starvation from losing a food source, or other challenges they might face in the wild.

Second, animals in captivity have access to medical care. For example, if an animal were to have an infected tooth in the wild if their body could not fight off the infection it might lead to difficulty eating. That animal could eventually starve to death, while an animal in the zoo has access to medical care for ailments like these.

That being said, keep in mind that just because an animal lives longer does not mean that it’s living to its highest standard. Some more intelligent animals are aware they are in zoos, or at the very least, aware that they are living somewhere and are not permitted to leave. Of course, some animals are also benefited from the zoo and they would not survive if they were released back into captivity.

Final Word

So, why do animals have short lifespans? Animals have short lifespans for several reasons. In the wild, they face a number of challenges that may cause them to perish. This is one of the reasons animals live longer in captivity.

There are also theories on animal aging and how it affects the lifespan of different animals. Animal size was once believed to have something to do with this, however, the number of neurons in an animal’s brain has been able to predict animal longevity with better accuracy. This may have something to do with brain aging and how it affects life.