Why Do Animals Age Faster Than Humans?

While there are animals who live longer than us--such as the giant tortoise (152 years) and the turkey buzzard (118 years), generally speaking we have a longer lifespan than most animals and seem to age slower than these animals. It is heartbreaking to the average pet owner when you only get to spend a small percentage of your life with your beloved pet. Unfortunately, there is not yet any concrete scientific explanation for your pet's short lifespan. However, there are some theories of why animals age faster than humans.

Size

The general school of thought has been that larger animals have longer life spans. However, scientists have found many flaws with this theory. When you consider that a chipmunk lives 14 years while a rat only lives three, you can see why there has to be more to an animal's lifespan than simply its size. The most obvious example is that we humans live an average of 70 to 75 years, yet we are smaller than a grizzly bear, which lives 32 years. This led to the theory that brain size was a factor in the body size theory. Therefore, one factor in why we live longer than other animals is that we have a greater brain-to-body size ratio than most other animals.

Metabolism

Another factor in life span and rate of aging is an animal's metabolism. Small animals generally have a faster metabolism. Considering an animal (including humans) has only a billion heartbeats before dying, the faster these heartbeats are used up, the sooner the animal will die. This causes smaller animals that have high metabolisms to age or to reach the end of their life span at a much more rapid rate than larger animals. As a larger animal with a slower metabolism, we humans are privy to a longer life span and a slower rate of aging.

Reproduction

Another factor that figures prominently in the aging of animals is the age of sexual maturity and the rate of offspring an animal can produce. Animals that quickly reach sexual maturity and have large litters will have a shorter lifespan. Humans take a long time to reach sexual maturity compared to other animals, and we generally only have one child at a time. Therefore, we need a longer lifespan and a slower rate of aging to replace our population. However, a mouse that reaches sexual maturity within several weeks of birth and is able to have litters of six or more young will have a shorter lifespan.

Theories/Speculation

In addition to size, metabolism and sexual maturity, there are some other reasons why we live longer than other animals. In accordance with sexual maturity being a factor determining lifespan, it is theorized that prey animals need to reach sexual maturity sooner because they live a more dangerous life and need to reproduce as soon as possible to re-populate the species. Humans who have no natural predators have the luxury of reaching sexual maturity at a slower rate and enjoying a longer life.

Exceptions

Aging and differences in lifespan are still a puzzle to the scientific world. As many guidelines as there are to understanding why we age at the rate we do while other animals age faster and have shorter lifespans, there are many exceptions to the rules. Birds, porcupines and bats all live longer than animals of similar size and circumstances. The naked mole rat, the same size as a mouse (which lives three years) lives an impressive 28 years. Gerontologists--those who study aging--continue to research in the hopes of discovering a fountain of youth, or at least figuring out the puzzle of why we age at the rate we do.

References

• Life Lasts About a Billion Heartbeats
• Longest and Shortest Life Spans
• Mad Sci on Life Span

Resources

• Why Do Animals Age?