Why Animals Have Different Life spans? By: Joao Pedro de Magalhaes

For the microscopic lab worm C. elegans, life equates to just a few short weeks on Earth. The bowhead whale, on the other hand, can live over two hundred years. Why are these life spans so different? And what does it really mean to ‘age’ anyway?

“In animal studies, maximum span is often taken to be the mean life span of the most long-lived 10% of a given cohort. By another definition, however, maximum life span corresponds to the age of which the oldest known member of a species or experimental group has died. Calculation of the maximum life span in the latter sense depends upon initial sample size.[1]

Maximum life span contrasts with mean life span (average life spanlife expectancy), and longevity. Mean life span varies with susceptibility to disease, accident, suicide, and homicide, whereas maximum life span is determined by “rate of aging”. Longevity refers only to the characteristics of the especially long lived members of a population, such as infirmities as they age or compression of morbidity, and not the specific life span of an individual.

Small animals such as birds and squirrels rarely live to their maximum life span, usually dying of accidents, disease or predation.

The maximum life span of most species is documented in the Anage repository.

Maximum life span is usually longer for species that are larger or have effective defenses against predation, such as bird flight, chemical defenses or living in social groups.

The differences in life span between species demonstrate the role of genetics in determining maximum life span (“rate of aging”). The records (in years) are these:

  • for common house mouse, 4
  • for Norway rat, 3.8
  • for dogs, 29
  • for cats, 38
  • for polar bears, 42 (Debby)
  • for horses, 62
  • for Asian elephants, 86

The longest-lived vertebrates have been variously described as

  • Macaws (A parrot that can live up to 80–100 years in captivity)
  • Koi (A Japanese species of fish, allegedly living up to 200 years, though generally not exceeding 50 – A specimen named Hanako was reportedly 226 years old upon her death)
  • Tortoises (Galápagos tortoise) (190 years)
  • Tuataras (a New Zealand reptile species, 100–200+ years)
  • Eels, the so-called Brantevik Eel (Swedish: Branteviksålen) is thought to have lived in a water well in southern Sweden since 1859, which makes it over 150 years old. It was reported that it had died in August 2014 at an age of 155.
  • Whales (Bowhead Whale) (Balaena mysticetus about 200 years) Although this idea was unproven at a time, recent research has indicated that bowhead whales recently killed still had harpoons in their bodies from about 1890, which, along with analysis of amino acids, has indicated a maximum life span, stated as “the 211-year-old bowhead could have been from 177 to 245 years old”.
  • Greenland Sharks are currently the vertebrate species with the longest known lifespan. An examination of 28 specimens in one study published in 2016 determined by radiocarbon dating that the oldest of the animals that they sampled had lived for about 392 ± 120 years (a minimum of 272 years and a maximum of 512 years). The authors further concluded that the species reaches sexual maturity at about 150 years of age.” https://en.wikipedia.org/wiki/Maximum_life_span

 

 

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