In the first chapter of his 2008 book The Living End: the future of death, aging and immortality, Dr. Guy Brown of the University of Cambridge cited the following Greek mythology: Tithonus was a handsome mortal who fell in love with Eos, the goddess of dawn. Eos realized that her beloved Tithonus was destined to age and die. She begged Zeus to grant her lover immortal life which Zeus did. Being jealous and deceptive, Zeus granted Eos’ wish without eternal youth that Eos had neglected to include in her wish. As Tithonus aged, he became increasingly debilitated and demented, eventually drove Eos crazy with his constant babbling. In despair, she turned Tithonus into a grasshopper (or cicada, according to some other versions). Well, this myth may explain why grasshoppers (or cicada) chirrup nonstop, like some demented old men. It raised obviously a much more serious issue – with aging, how desirable could immortality possibly be?
Physical mortality and death must have started as a fairly straightforward notion since it is a visible certainty in life. Dr. Brown calls it the digital theory of life and death; either one is clearly alive or dead, that is, it is either on or off like many familiar devices such as light bulb. For some mysterious reasons however, we seem to be reluctant in accepting death and consequently continue fighting it with fear. This might be more understandable in ancient days when people generally die at a much younger age and we can attribute it to animal’s survival instinct. However, life expectancy of people (at birth) has increased dramatically in last 200 years. It has more than doubled from 30 years to 67 years by the beginning of 21st century. There is no known evolutionary reasons why we need to hang around way after the prime age of reproduction!
Nevertheless the continual increase of life expectancy sounds so promising and tempting, doesn’t it? If the rate of increase holds up and continues, perhaps we can be approaching immortality! Well, it is not so simple. The primary reasons for the significant improvement of the last 200 years were better public health and nutrition. As a result, the leading causes of death then such as infant mortality childhood death and death due to infectious diseases were greatly reduced. For a fascinating visualization of the story, see the following video 200 years that changed the world by the Swedish Professor of International Health Hans Rosling. By the way, wealth beyond some low threshold, is not necessary for high life expectancy. Indeed there isn’t whole lot of differences (less than 10 years) in life expectancy between developed and developing countries. Experience in 1950’s China demonstrated it clearly although the country was extremely poor.
The bad news is if one distinguishes the healthy vs. unhealthy parts of our life expectancy (at birth), Professor Brown showed evidences from UK (thus likely similar for other developed countries as well) that the unhealthy part of late life is the one being extended while the healthy part increased at much slower rate for the last two decades of the 20th century. In other words, the data support the prediction of The Failures of Success by late Professor Ernest Gruenberg of Johns Hopkins University that expansion, rather than compression, of morbidity - diseased state - is happening. At least partly to blame is our relentless efforts in advancing medical technology to prolong life at all cost. Death is no longer short or quick. Death is a taboo; we herded the old and sick into nursing homes and hospitals to die in desolation. The boundary of death and aging is getting blurred as we are left bare, dying alone ever more slowly with possibly agonizing chronic diseases such as dementia.
A digression; you may ask what is aging anyway? Can we alter it? The first reaction by most of us is likely to associate aging with the “chronological age” which gives a numerical measure of the progression towards to the inevitable but unknown time of death. Behind the chronological age are the more familiar and common signs of aging. Ted Fishman gave a long list of them in his 2010 book Shock on Gray which includes: in 30’s, our metabolism begins to slow down and body to begin redistribute the fat and lose muscle mass and strength; in 40’s, our joints begin to stiffen, hairs begin to turn grey, and vision begin to decline; in 50’s, we begin to forget things, gums start to recede, and for many, high blood pressure, blood sugar, and cholesterol arrive; in 60’s, our skins begin to change with age spots and we begin to walk more slowly and lose some hearing; in 70’s, we have more and more memory lapse, we lose our balances more often and our sensory functions deteriorate visibly; in 80’s, we lose the fat under our skins that now appear thin and saggy, and a significant number of us suffer from dementia.
These signs, while useful in sharing astute observations, are qualitative and less than satisfactory for scientists. One more useful and robust quantitative measure of aging is the rate of aging which is defined as the mortality doubling time, or the amount of time it takes for the population death rate to double.
Surprisingly the Mortality Doubling Time is basically a constant for each species when deaths caused by external events are negligible. It is about 1-2 years for dogs and 14 years for killer whales. For humans, the death rate doubles about every 8 years for population between ages 30 and 80 which is the Gompertz Law of human mortality, named after the English actuary Benjamin Gompertz who discovered this constant in 1825. Not that this law is of fundamental importance to life insurance business as we know it today. It also supports the hypothesis that the “max” life span of human is about 125 years although there are some believe that figure can be much higher as the mortality doubling time appears to slow down after age 80.
Interestingly, human mortality doubling time has not changed since the Stone Age although the value of death rate itself has decreased significantly especially in the last two centuries as we mentioned earlier. Note also that even though the expected lifespan of humans has increased significantly, the appearance and functions of say a 65 years old man a century ago is still more of less the same as those of today; the signs of aging remain pretty stable by age. All these suggest that there is a biologic limit in life. They beg for an answer to the question of why or how does aging work.
At a micro level, there have been many theories and hypothesis about why and how cells die but many mysteries remain. What we do know for some time from modern biology is that each of us is made of about 100 trillion cells where cell is considered the basic functional unit of all known living organisms and is the smallest unit of life. We now know that cells are programmed to die to, e.g., make room for other or new cells to grow and to perform designed functions. Cells may also experience accidental or disease-induced death due to insufficient oxygen and energy/glucose supply from the blood flows. We also know by the Hayflick limit discovered in 1961 that normal cells cannot replicate indefinitely. The bottom line is at the cellular level, normal cells are not immortal and will die in finite time.
At a more macro level, we understand that cells from the same origin together form tissues to perform particular functions and multiple tissues together then form a structural functional unit referred to as organ such as lung, bladder, heart etc. Cells are born, aged, damaged and repaired (for some), and eventually commit suicide or killed. Today’s medical advances have reached a point where we can repair some tissues with stem cells, we can replace parts or whole of some organs including the lung with other’s or with an artificial one. Is immortality possible then even though individual cells are dying at different rate? Have you seen this wonderful British science fiction television series Doctor Who and the arch-villain mad scientist Davros? What does it mean to be immortal if parts or all of us have been replaced or “enhanced”? Are you still yourself?
The key must ultimately lie with the brain. Other than heart cells, neuron is the only cell that cannot be replaced. That is why strokes (and heart attack) can cause irreversible damages once neurons (and muscle cells) are suffocated or scarred. More importantly, unlike heart which is the (mechanical) pump that keeps our organs alive with supplies, brain is defining who we are as it receives and processes signals, and issuing signals that command our body. It weighs only about 3 lb with a volume of about 1130 cm3 for women and 1260 cm3 in men. Some estimated the human brain has about 100 billion neurons and more than100 trillion chemical, electrical and immunological synapses. These neurons develop and work together to perform our daily functions such as muscle control, memory, cognition, language, etc. We pay a 20% premium of our energy consumption to keep it active and healthy. For these and other reasons, clinically, death is defined today as an absence of brain activity (as measured by EEG). A more intuitive and philosophical definition is, as Dr. Brown suggested, “the permanent loss of consciousness.”
Wikipedia entry of consciousness refers to it as “a variety of aspects of the relationship between the mind and the world with which it interacts”. It also refers as to common definitions such as “subjective experience; awareness; the ability to experience feelings; wakefulness; having a sense of selfhood;” etc. Indeed, as we are born, grow and develop, we continue to accumulate our experiences and undergo changes at every level.
If you think further, the continuity of self is actually maintained through our memory which is formed and shaped from vague and fluid associations of fragments of data scattered among huge number of neurons, unlike digital computers. When youngsters and adults suffer from neurological diseases or brain dysfunction, we consider them “abnormal” inferring from their behaviors and interactions. When old people developed dementia – loss of cognitive ability, we refer them as “not behaving like themselves, erratic, or hallucinating”. (By the way, as a side note, more than 15% of people over age 70 are believed to have some forms of dementia and this percent is expected to increase.) When some suffer from late stage Alzheimer’s disease, there is only present and there is no past any longer. The continuity through memory has been broken and the individual can no longer interact with the world as we know. Where is the self and consciousness then even though he or she is physically alive?
The silver lining is that there are many known ways to address the fear for death and mortality beyond the physical. At the instinctive level, evolutionary needs necessitate our survival genetically via reproduction which is manifested through off springs and families. Our ancestors have also found a long time ago that we one can become immortal by leaving our work, deeds and legacy that are carried forward, however little, indefinitely as parts of the culture and the society. For those who are more curious about the after-life, there is always the religion that has developed various theories and teaches people how to live their lives and deal with death.
For myself, being pragmatic, I would follow Confucius’ 2,600 years old advice in his Analects: Ji Lu asked about serving the spirits. Confucius said, “If you can't yet serve men, how can you serve the spirits?” Ji Lu added, “May I ask about death?” Confucius said, “If you don't understand what life is, how will you understand death?”(translation by Charles Muller) 子路問事鬼神。 子曰：'未能事人，焉能事鬼？ ''敢問死。 '曰：'未知生，焉知死？ '”《論語·先進》
Talk to you soon!
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