What is Life span? Life span – Definition
Life span is the period from birth to the natural death of an entity.
The life span of an organism is the theoretical figure indicating the number of years it lives. It can be estimated by the average life span of the entity. It varies between individuals and species based on their type, ranging from a few minutes to some days to several years.
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The life span of a particular entity is based on different aspects, genetically determined. The human-life expectancy for instance is approximately 120 years. Life span is an epidemiological standard, which is estimated as the average age of death in a popular cohort.
Life span development
Life span development is the field of study that analyses the patterns of change, growth, stability in the behaviour, occurring all throughout the life span of a species through a scientific approach.
Life span of some species – Examples
The table below shows the life span of different species –
|Life span (maximum)
Factors Affecting Life span in Humans
Some of the factors that affect the life span of human beings are listed below –
- Factor of heath
- Infant and childhood mortality rate
- Prevalence of diseases
And some other factors which may be related to an epidemic/pandemic, unforeseen calamities etc.
Some causes of death in the world
- Heart ailments
- Cerebrovascular diseases
- Lower respiratory diseases (chronic)
- Alzheimer’s disease and dementia
- Chronic renal failure
Reproduction and its Purpose
One of the basic life processes that living entities exhibit is the process of reproduction. It is a biological process wherein an entity gives rise to its younger one. This characteristic exhibited by living organisms is significant.
Why must reproduction take place?
Reproduction must take place because of the following reasons –
- To ensure the continuity of species – the process maintains continuity of species
- Species is organised – the process of reproduction maintains the population of all age groups
- Introduces variations – reproduction is important as it brings about different variations in species, survival of the fittest aspect is covered. Beneficial variations in the species are required for adaptation and evolution
- The process of reproduction ensures life exists and sustains on earth
Characteristics of reproduction
While there are types of reproduction – asexual and sexual reproduction, yet there are some basic features that remain the same, regardless of the type of reproduction. Some of the basic features of reproduction are –
- DNA is replicated
- Proteins, RNA and bio-chemicals are synthesized
- Cells grow and undergo division
- Reproductive parts are formed
- New individuals are formed
Life span vs. Life expectancy
Life span or longevity is the length of time a species can exist in the most optimal conditions. For example, the gray wolf can live for 20 years in captivity, the Galapagos tortoise for over 150 years. On the other hand, life expectancy is the predicted number of years a person born in a specific time period can reasonably be expected to live. In other words, it is the average number of years a person born in a particular country would live, if the rate of mortality at each age were to remain constant in the future.
Life span of humans vs. Expectancy
Both the terms, like span and life expectancy, are correlated to the number of years living but in fact, they represent different concepts.
Life span in humans is the maximum number of years a person can live while the life expectancy of an individual is the estimate or an average number of years a person is expected to live. The life expectancy is imputed to an individual’s health history, lifestyle, genetics, while the life span is for all the living humans.
The life expectancy of a person is affected by some factors such as environment, family history, age, sex, diet. The life expectancy of a person can be different from the other person’s and is subject to change over time. However, the life span remains the same.
Life span of humans
It can be defined by the longest noted life of humans from birth to death which, over the years, has changed. Currently, for humans, the accepted maximum life span is 122 years. Jeanne Calment (1875–1997) of France is known to be the oldest person ever, whose age has been verified as 122 years and 164 days. There are claims of people having lived longer too, however, none are verified and documented for now.
Prenatal period – It begins at conception, continuing through the implantation in the walls of the uterus by the embryo and ending at birth.
Period of Infancy and toddlerhood – It begins at birth, continuing up till 2 years of age.
Period of Early childhood – It begins at two years of age, spanning up till 6 years of age.
Period of middle and late childhood – It begins at age 6, continuing up till the onset of puberty.
Period of adolescence – It begins at the onset of puberty up till age 18.
Period of emerging adulthood – It begins at 18 lasting up till 25.
Period of early adulthood – It begins at age 25 lasting until age 40 to 45.
Period of middle adulthood – It starts at age 40-45 lasts until 65 years of age
Period of late adulthood – It begins at age 65 onwards
Life span Measurement
The maximum span of life is actually a theoretical figure, the exact number cannot be specified from the knowledge of an entity that prevails now. Often, it is provided as a ballpark estimate on the basis of the longest-lived entity of that species, which is known till date.
A more indicative assessment is the average life span, which is a statistical theory obtained by the study of mortality information for the population of each of the species. A closely associated term is life expectancy, a speculative number estimated for humans from the mortality data extracted from insurance firms, that were born in the same period, probably expected to live and depends on the fluctuating mortality rate over the years.
Determination of life span
The idea of life span indicates that there is a being who has existed with a definite start and end. The start of an entity is the formation of the zygote (fertilized egg) in the sexual mode of reproduction or by the literal disintegration of the new entity from the parent entity in the asexual mode of reproduction.
Generally, in animals, birth is deemed to be the start of the life span. However, the time of birth varies in different animals (based on different criteria).
In several marine organisms, the larva that is hatching comprises comparatively lesser cells. The variation even in mammals is substantial.
At birth, a kangaroo is approximately an inch long which must further develop in the pouch, which cannot be compared to a deer that is just born, who starts walking in minutes. In the event where the life span of different entities is being compared, it is necessary to take into account these variations as well.
The end of the existence of an entity is when changes (irreversible) have taken place to an extent that the entity cannot further retain actively. Subsequently, there is a brief duration at which time it is not possible to comment if the entity is alive, however, this is a short-lived span in comparison to the total life span.
On the contrary, there are other entities that appear as immortal potentially, until there is an unforeseen circumstance that ceases life. Until then, they seem to be fully able to indefinitely survive. This capability has been ascribed to some reptiles and fishes, demonstrating indefinite growth. Entities that are difficult to define in colonial forms apparently do not seem to age.
Life span of Plants
Plants are known to survive for long periods of time, as do some animals. There does not exist an accepted definition for the age of plants, as of now. However, if the age of a plant is the time duration between the reproductive process producing the individual and the death of the individual, the age of it can be readily provided for some plants, but not for others.
Some of the plants have a shorter life span (as less than a year), some others live upto centuries. Plants are known to be the longest-lived entities. The Bristlecone pine tree, for instance, found in eastern California is 4900 years old.
The life span of plants depends on two factors – genetically defined potential for longevity and the effect of the environment which include weather and soil conditions, diseases causing herbivores and microbes.
The age of some plants is as tabulated below –
|Life span (maximum)
|Common juniper (Juniperus communis)
|544 years (verified)
|European beech (Fagus sylvatica)
|815 years (verified)
|Blueberries and sumacs
This was a brief on the life span of organisms, the life span of humans, the life expectancy of organisms, the life span of plants, measurement of life span, reproduction and its purposes.
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