Every living species on earth has a definite lifespan. What is the life span of humans and what is its upper limit in yearsIJ With improvement in healthcare, sanitation and better standard of living, the average life span of humans has increased from 31 years in 1900 to 66 years in 2000 AD.
The number of people living up to 100 years or more has increased. Due to technological advance, old age mortality has been considerably reduced from 19th to 20th century. Some of the scientists believe that if the current trend continues the average life span will increase by 2 to 3 years per decade and most of the babies born in 2000s will celebrate their 100th birth day (Christensen and coresearchers, 2009; Kurzweil and Grossman, 2010).
How long the life span of human beings can be extendedIJ Is there a possibility that undefined scientific breakthrough might ensure physical immortality of humansIJ
Dong and coresearchers of Albert Einstein College of Medicine, New York, analysed global demographic data and reported (Nature, 2016) that the maximum life span of humans is fixed and subject to natural constraints. The average age of oldest persons at death has not increased since 1990.
Adrian Marck and his coresearchers at the Institute of Biomedical Research of Epidemiology of Sports in France published a comprehensive paper entitled ‘Are we reaching the limits of Homo sapiensIJ’ in Frontiers of Physiology in September 2017. Ageing is a complex and irreversible process. All physiological functions, organs and their maintenance system maximise in the third decade of life and decline exponentially thereafter until death.
Recent research results indicate that with all the technological advances in healthcare, nutrition, sanitation and standard of living the average life span of humans is 85-95 years and maximal longevity 115-125 years.
A graph plotting maximum life span over the years has plateaued around 115-117 years. We are probably very close to our limits of longevity.
The fully authenticated age to which humans ever lived is 122 years 164 days by Jeanne louise Calment (France).Masazo Nonaka of Japan, who is 112 years old currently holds the world record of oldest living person.
There has recently been a claim (TOI, May 19, 2018), that Manuel Garcia Hernandez from Mexico, born on December 24, 1896 is 121 years old and might be the oldest. He feels as if he is 80 years old and raise chickens to keep him fit. He hopes to live to 125 years. (life expectancy in India 2010-14 is 67.9 years and of Odisha 65.8 yrs. UNDP).
The recent scientific studies link our life span with structures in our chromosomes known as telomeres.
These consist of two RNA caps on both sides of each pair of our chromosomes, which are made up of DNA and proteins. The RNA caps consist of long chains of purine and pyrimidine bases, which are the components of RNA.
As we age and suffer from diseases, a few of the bases are lost, shortening the RNA chain. When the protecting RNA chains are completely lost, the chromosomes disintegrate resulting in death.
longevity depends on lengths of telomeres at birth and rate of shortening of RNA chain with diseases and ageing. Steenstrup and coresearchers, (2017) measured leukocyte Telomere length (lTl) of European population and observed that alimitinglength of 5kb(5000 purine and pyrimidine molecules)indicates imminent death. This is reached by most of the people when they are at an age of 100 years.
Another debate now in progress is the upper limits of physical performances by humans, for example in sports by men and women. There is a common slowdown in both frequency and increments of all Olympic chronometric and metric events (track and field, swimming, cycling, skating and weight lifting etc.) during last three decades indicating a trend towards approaching a limit.
The human body is a finite organism with structural components such as, 640 muscles and 206 bones, limited by functional boundaries at every level of organisation.
The normal human resting heart has 45-100 beats per minute and can reach a maximum of 220 beats during intensive efforts.
The maximal capacity of human performance is reached in the third decade of life and then declines.
Every other organ of the human body has such age dependant limits. Physiological limits of human body restrict their physical performances within certain limits.
Bio-mechanical and physiological investigations including structural and functional factors such as, limiting oxygen uptake, maximal heart rate, muscle mass and contraction, reaction time, stature, stride length and frequency, indicate that, we are probably approaching the potential upper limits of physical performances of Homo sapiens.
The increase in adult human height is the third parameter, which appears to be reaching its limit.
A taller person is associated with longer life, better personality, higher education and earnings. Eduardo Franco of McGill University, Canada published a paper in elife(2016), a 1472 population-based study, which examined change in adult heights of more than 18.6 million people from 200 countries born from 1896 to1996.
Heights of people from countries differed due to their genetic differences. However, increase in average adult heights in each country was not linear and showed a tendency to reach a plateau over the century in spite of significant changes in their economic status, access to healthcare and adoption of modern technology.
There has been virtually no change in the average heights of tallest adult population of economically developed countries, in the last three decades, indicating plateauing of this parameter.
We have probably reached the upper limit or very close to maximum average adult height of Homo sapiens. There are of course phenotypic exceptions in individual adult heights of tallest and shortest person.
Both the extremes generally induce severe pathological conditions and health risks. (Currently Sultan KÖsen of Turkey, 251 cm (8 ft 2.8 inches) holds the world record of tallest person and India’s Jyoti Amge, 62.8 cm (2ft 6 inches) the shortest).
Some of the scientists believe that through genetic manipulation of human genome we can increase our life span and physical capabilities (Kruzewell and Grossmann, 2010).
A term ‘Transhumanism’ is now in currency among some of the scientists (Max More, 1990). It is iteration that Homo sapiens can overtake biological evolution but essentially remain human.
A new and enhanced human being is likely to be created in future through genetic engineering, epigenetics, synthetic biology, bioengineering, artificial intelligence, robotics and many other future innovations.
He will behave as a normal human species but with abnormal capabilities. (Pl. read an earlier article on CRISPR published by the author in this column, The Pioneer, June 20, 2018).
Many scientists have questioned, ‘Is it ethical to accept such interference in human evolution’ (Trippett, 2018). Several research publications and books have been published cautioning creation of a superhuman race and its possible impact on the society.
Evolution of humans by natural selection is still in progress (Mostafavi and coresearchers, 2017) but it is a very slow process.
The irreversible climate change scenario projects a hostile environment on earth for survival of our future generations probably as early as the end of this century.
If normal biological evolution cannot create Homo sapiens, who can survive in such hostile environment, ‘Transhumanism’ may be the answer.
(Dr Mitra, a former Dean and Professor, OUAT is a teacher and researcher. latest publication (June, 2018) a chapter in a book by Springer (Germany). References quoted are available through internet. Email: gnmitra@gmail.com )