Being mortals, we have to face death at some point or the other, but we cannot predict the exact time of your death, or can we? According to some researchers, there might actually be a way of predicting when we are going to die. Until recently, it was believed that only 2 phases of life existed – childhood and adulthood. During childhood, you grow and develop rapidly and when you mature sexually, you become an adult. As a young adult, your chances of death are low because you are physically at your best and you tend to reproduce during this phase of your life. As you mature further, your body begins to wear down and your chances of death increase. Each passing year is one step closer to death.
During the early 1990s, researchers found that one more phase of life exists apart from childhood and adulthood. When they performed some experiments on fruit flies, they discovered that these flies go through a new and distinct phase of life as they near death called late life. They believe that humans too experience this phase of life. The difference between late life and adulthood is the pattern of mortality. The increase in the possibility of a person’s death with each passing year is not applicable to late life. At some point in life the mortality rate levels off. A 90-year-old person and a 100-year-old person have the same chances of dying.
There is no accepted explanation as to why mortality plateaus occur so Laurence Mueller at the University of California and Rose along with her students looked for other physiological features that leveled off during late life. They conducted research on Drosophila fruit flies and checked if their fertility leveled off too. They took 2,828 female flies and counted the number of eggs each one laid each day until they died. The initial results were disappointing as the fertility rates did not level off as the flies entered late life, but they discovered something entirely different going on. Even if 2 flies were of the same age, there was a difference in the fecundity of the one which was close to death and the one which still had several more weeks to live. A fly’s fertility rate dropped considerably 2 weeks before she died. The drop in fertility of a 60-day-old fly was the same as the drop in fertility of a 15-day-old fly which was nearing death. They termed this fourth phase the “death spiral.” More research was conducted on the death spiral by other researchers and it was found that even male flies experience a drop in fertility as they approach death.
James Curtsinger at the University of Minnesota also found this drop in fertility in flies during the days leading up to death, regardless of their age, but he did not fully agree with Mueller and Rose. He was not convinced that species which were biologically different from fruit flies also experienced this fourth phase of life. He also found the term death spiral vague and devised his own concept, retirement. He says that “retirement” begins the day a mature female fly does not lay a single egg. Fruit flies measure 2.5 mm and their eggs 0.5. They lay 1,200 eggs in their entire life, which is almost 0.5 m when you arrange them in a straight line. So when a fly does not lay an egg for an entire day, it clearly indicates that something is not right. He also found that flies experienced mortality plateaus associated with late life at the end of the retirement phase.
Many researchers these days are of the opinion that age and mortality plateaus are interlinked, but according to Curtsinger’s work, mortality plateaus may be more connected with fertility. James Carey at the University of California in Davis conducted experiments on the reproductive system of mice and found that replacing worn ovaries with young ones extended their lifespan. They also had fewer heart problems. Curtsinger does not fully believe that humans too go through a retirement phase before death. According to Mueller, people who are going to die of a natural cause may experience a death spiral. Some researchers have also found that people experience a decline in physical capabilities as they approach death.
Studying about life and death is quite interesting. The main aim of the studies is to prevent people from going through the tedious decline in health as they approach death. They can be as healthy as they can be until their time comes to leave this world.
