An important characteristic of post-embryonic development is the extent of its length in time, which is called the life expectancy . Different kinds

Life expectancy [span, Longevity]

An important characteristic of post-embryonic development is the extent of its length in time, which is called the life expectancy. Different kinds of organisms have unequal duration of life; it is usually higher for larger organisms with a slow rate of growth and maturation. In higher animals long-lived species are with a well-developed brain. Humans are also considered as centenarians.

Life expectancy in different species of organisms is very different. Single-celled creatures live active (not in the form of spores or cysts) at most — few days, whereas the life of multicellular organisms is stretched sometimes for hundreds of years. Obviously, the more cells has the body of an organism and the more complex its structure, the more reliable its functioning and the slower goes the aging process — a process of gradual loss of normal functioning, loss of ability to reproduction and restoration of damaged tissues and organs. Aging body loses its ability to quickly adapt to the environment, to resist various infections. The aging process inevitably leads to the natural death — an irreversible termination of organism functioning. But it turns out, multicellular organisms that belong to the same phylum, class and order also usually have different longevity. And the differences in maximum life expectancy of representatives of the same class of vertebrates may be in two, three, ten or even a hundred times (see table).

Maximum life expectancy

Table. Maximum life expectancy of different species of vertebrates

Vertebrates group

Species

Maximum life expectancy

Mammals

Polar whale

210

Human

122

African elephant

86

Chimpanzee

75

Dog

34

Squirrel

16

House mouse

4

Birds

Vulture

118

Swan

70

Dove

23

Swallow

9

Hummingbird

4

Reptiles

Galapagos tortoise

177

Nile crocodile

68

Sand lizard

8-10

Fishes

Sturgeon

160

Catfish

60

Crucian carp

15

Guppy

3

Researches of scientists give grounds for assuming that the maximum life span of individuals of a particular species clearly depends on its biological features. The ideal kind of long-living mammals — is a large animal with a sufficiently long period of puberty and a few offspring. Also it was found that slower aging have animals with a large brain and low metabolic rate. Based on these criteria, all large mammals, especially whales, elephants and human in ideal conditions have to live a long life (a higher life span), and tiny shrews or prolific rodents, even if they get rid of enemies and heal from disease, will still have a short life (a lower life span). A similar pattern can be easily traced not only in mammals but also in other vertebrates: fishes, reptiles and birds.

Reasons of difference in life expectancy

What is the reason that large animals have a higher life expectancy? First of all, they grow longer because of the large size, and therefore ripen later. In addition, it is well known that large organisms have much lower metabolic rate than the smaller species of near systematic group. This means that per unit of time, they consume less energy and matter, that is, saving their vitality. Taken from http://worldofschool.org

Time, like all other physical quantities — is a relative term. Therefore, the duration of the life of any organism can be evaluated as by means of astronomical clock in days and years, as well as by means of biological, based on the internal rhythms of the organism’s vital functions. It is known that in smaller organisms the rate of metabolism is higher than in large individuals or related species. Accordingly, relatively small specimens of vertebrates breathe more often, their heart is beats at a higher pace. This feature of biological clock confirm the smallest mammals — shrews, in one day manage at least four times to hunt and four times to sleep. It is obvious that during a single rotation of the Earth around its axis they live several biological days, and a month of their life, perhaps even equals for an astronomical year. So, if as a criterion of longevity consider not the clock, but periodic events occurring in the organism, it is quite reasonable to raise the question, who has a higher life expectancy: she-wolf, who during her life span give life to several dozen of children, but living at most 30 years, or the elephant, who give birth to three or four elephants, the longevity of which six or seven decades.

Questions:
  • What is life expectancy?

  • What are the reasons for life expectancy differences in vertebrates and insects?

  • What features are typical for long-living animals?

  • What organisms should be regarded as the greatest longevity and what age do they reach?