Aging is considered inevitable. All living things must undergo the cycle of life, from the tiniest hedgehog to the great bowhead whale. Given, the maximum lifespan for these animals is different, as the hedgehog at most lives 3 years while the bowhead whale can live up to 200 years. However, the existence of the Turritopsis jellyfish defies this natural law as it is, theoretically, immortal. What decides the differences between these species? And how does this affect how we, as humans, perceive age?

Table of Contents

• Senescence and Negligible Senescence
• Aging in Simple VS Complex Animals
• Potential Causes for Aging
• Immortality?

Senescence and “Negligible” Senescence

         Senescence is defined as the process of aging, while “negligible” senescence describes living beings that age so slowly that they practically do not age at all. For example, Greenland sharks, Galapagos tortoises, or the previously mentioned Bowhead whales all live, on average, more than 100 years. These animals would be considered to have “negligible” senescence.

Aging in Simple VS Complex Animals

         Some of the longest living animals are the simplest, like sponges, sea anemones and jellyfish (like the Turritopsis jellyfish). These animals maintain stem cells, which are cells that can self renew and generate different cells, to regenerate themselves.

         Yet it seems that, due to evolution, this ability decreased as animals became more complex. Simple organisms like flatworms can live indefinitely due to their stem cell systems. More complex creatures, including humans, have traded this ability for increased sophistication and protection against uncontrolled cell growth. Even so, there is no direct correlation for longevity and complexity.

Potential Causes for Aging

         As some of the oldest theories surrounding aging, “wear-and-tear” theories propose that a part of aging has to do with the buildup of genetic mutations and general unreliability. As small mutations build up, slowly the efficiency of enzymes that make the body work decreases and senescence happens.

         Metabolism is the process of turning food into chemical energy to be used in the body. When animals age this process slows down and increases the amount of fat whilst decreasing the amount of muscle. This further increases the likelihood of getting metabolic diseases such as type II diabetes and hypotension.

         Genetics play a role in aging as well. For example, in humans, Hutchinson-Gilford progeria syndrome demonstrates how a single dominant mutant gene can cause rapid aging and premature death. A similar syndrome in mice, caused by mutations in the klotho gene, highlights the potential for genetic manipulation of aging pathways. These genes are suspected to control the aging process.

         Other than the factors mentioned above there are numerous others, both internal and external, that help explain why an animal lives more or less than other animals.

Immortality?

         Right now, there is no immediate cure for mortality. Neither is there only a sole factor for longevity. Even so, animals that can efficiently repair DNA are hypothesized to live longer. Possible ways to improve metabolic rate include building muscle mass through resistance training or undergoing caloric restriction, which is reducing caloric intake without malnutrition.

         Even if there is no legitimate way to stop the process of aging, understanding the biological mechanisms of it allows us to confront mortality with greater acceptance and purpose. We can recognize that aging is a natural, complex process rather than an arbitrary endpoint.