According to which theory, ageing is due to accumulation of harmful protein?
Answers
Most people will live to experience ageing. Age-related deterioration is affecting an ever-growing number of people. Although the process is unavoidable, if we better understand the process, as a physiotherapist, it is important to understand that we might be able to positively influence aspects that maintain or engender better health and wellness as a person ages, treating and ameliorating symptoms of common conditions associated with ageing.
In the past, maximum life span (the maximum biological limit of life in an ideal environment) was not thought to be subject to change with the process of ageing considered non-adaptive, and subject to genetic traits. In the early 1900s, a series of flawed experiments by researcher Alexis Carrel demonstrated that in an optimal environment, cells of higher organisms (chickens) were able to divide continually, leading people to believe our cells to potentially possess immortal properties. In the 1960’s Leonard Hayflick[1] disproved this theory by identifying a maximal number of divisions a human cell could undergo in culture (known as the Hayflick limit), which set our maximal life span at around 115 years. Life span is the key to the intrinsic biological causes of ageing, as these factors ensure an individual’s survival to a certain point until biological ageing eventually causes death.
There are many theories about the mechanisms of age related changes, and they are mutually exclusive, no one theory is sufficiently able to explain the process of ageing, and they often contradict one another.
Modern biological theories of ageing in humans currently fall into two main categories: programmed and damage or error theories.
The programmed theories imply that ageing follows a biological timetable (regulated by changes in gene expression that affect the systems responsible for maintenance, repair and defense responses), and the damage or error theories emphasise environmental assaults to living organisms that induce cumulative damage at various levels as the cause of ageing[2].
These two categories of theory[3] are also referred to as non-programmed ageing theories based on evolutionary concepts (where ageing is considered the result of an organism’s inability to better combat natural deteriorative processes), and programmed ageing theories (which consider ageing to ultimately be the result of a biological mechanism or programme that purposely causes or allows deterioration and death in order to obtain a direct evolutionary benefit achieved by limiting lifespan beyond a species-specific optimum lifespan (Figure 1).
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Figure 1: Evolutionary cost/ benefit of additional lifespan vs. age.
Curve 1: Modern non-programmed aging theories – The evolutionary value of further life and reproduction is effectively zero beyond some species-specific age.
Curve 2: Modern programmed aging theories – There is an evolutionary cost associated with surviving beyond a species-specific age.
Curve 3: Medawar’s concept – The evolutionary value of survival and reproduction declines with age following a species-specific age[3].
Goldsmith's review of modern programmed (adaptive) theories of biological ageing investigates how organisms have evolved mechanisms that purposely limit their lifespans in order to obtain an evolutionary benefit.