Death is inevitable. But predictable? Some scientists think it is. They say that experiments with fruit flies — fruit flies — revealed a new distinct phase of life, which heralds the approach of death. This stage of life they call a death spiral and I think that people can survive.
25 years ago biologists thought that life has two main phases: childhood and adulthood. This separation we can all recognize. Childhood is characterized by rapid growth and development and ends with sexual maturity. During this phase, the probability of death is extremely low.
Along with the majority, but rather with the attainment of puberty, adult life. The probability of death is low, when we start our adult life — at this time we are in the Prime of life and are more likely to have children. But time passes, our bodies begin to age and deteriorate. With each city the probability of death increases — at first slowly and then faster and faster as we become older and older.
In the early 90-ies the scientists realized that life has another part. They identified the third phase of life through which the oldest members of our society: the late life.
Late in life from the rest of adult life characterized by the unique structure of mortality. The annual growth of mortality, which is a characteristic feature of adult life, does not apply to later life. If 60-year-old the chance of imminent death is much higher than the 50-year-old, 90-year-old the chance to die is about the same as 100-year-old.
“The mortality rate flattens out and you see these plateaux,” says Laurence Mueller of the University of California, Irvine.
It is these plateau mortality are discussed to this day they still have no single explanation. To shed light on this issue, Mueller and his colleague Michael rose began to look for signs that other biological features, not including mortality, even to the end of life. “We thought that there may be the same circuit that carries the reproduction or female fertility (fertility),” he says.
They began to study this problem on the example of the beloved set of laboratory animals — fruit flies Drosophila.
“We took 2828 females and placed each one individually in a vial with two males,” says Mueller. “Every day we moved each female into a new vial and counted how many eggs they have left. And kept doing it until they all died.”
Usually these flies live for several weeks. “It was a massive experiment,” says Mueller. He admits that the experiment also was hard to move so many flies every day and count their tiny eggs — from this you get tired quickly. Engaged in graduate student rose Kassanda the Rauzera, and dozens of students.
And after all these efforts, the results initially seemed disappointing. The birth rate is not aligned in an obvious manner, when flies entered the phase of “late life.”
When scientists looked at the data closer, they know what I noticed.
“I noticed that if isolated females that were close to death, and compared them with the other females of the same age and, as follows from the database, which remained live for a couple more weeks, there was a difference in fertility,” says Mueller.
Simply put, the birth rate of flies — the number of eggs laid per day — dropped sharply two weeks before their death.
Even more surprisingly, this decline in fertility had nothing to do with what was the age of the fly at the point of death. If the old 60-day fly was close to death, her fertility rate dropped sharply, the same as the fertility rate 15-day flies, which, as it turned out, was on the verge of premature death.
It was a universal feature of life, a new fourth phase that is different from the childhood, adult or late life. Mueller and rose called her the “spiral of death”. Was 2007; in subsequent years, scientists searched for more evidence of this death spiral. In 2012, they found that the males of Drosophila were undergoing a similar decline in fertility a few days before death. Repeated data collection at this time was engaged in post-graduate student, Parvin Shahrestani.
“As soon as the male gets older, its ability to impregnate females is getting worse and worse,” says Mueller. But when males are going to die — at any age — their ability to reproduce was much lower than males of the same age, who lived for a few weeks more.”
Recently, in 2016, Mueller and rose have extracted the data from a series of experiments exploring the longevity and fertility of fruit flies worked out by scientists in four independent from each other laboratories. Again, the combined data set showed the presence of a helix of death.
Two scientists and their colleagues even found that with a certain degree possible to predict when the fly will die just by looking at her fertility in the previous three days and ignoring other data, including the age of the flies. “We accurately predicted about 80% of the deaths,” says Mueller.
Rose and Mueller is not alone in developing this connection between birth and death. James Curtsinger from the University of Minnesota conducted his own experiments in the field of aging and death over blown and revealed a decrease in fertility in anticipation of death, which generally correlates with the findings of Mueller and rose.
Curtsinger also found that this decline in fertility due to the imminent death does not depend on age: relatively young and old flies followed the same script.
However, the work of Curtsinger differs from the work of Mueller and rose in several important respects. For example, he believes that his observations on the individual and the universal fourth phase of life — he did not believe that humans or other species, who are biologically different from fruit flies, will experience a similar decline in fertility. He also believes that the term “spiral of death” is vague and ambiguous. He therefore developed its own terminology that may come to mind biologists.
“When I was 20, I investigated the sex ratio; when I was 40, I started to work on aging — now I am 65 and I work on a new biological concept that I call resignation (retirement),” he says.
This “retirement”, it is easy to see fruit flies. It begins the day when the adult female can not have to postpone any. To understand the importance of this “day zero eggs”, we need to think about fertility of the female fruit fly. “Front sight 2.5 mm in length, and the egg of the fruit fly in a length of 0.5 mm,” says Curtsinger. — The female lays about 1,200 eggs in my life — a half-meter eggs, if placed in line.
In other words, the female fruit fly is a machine for oviposition. It’s the only thing on her mind. If the moth lays a single egg in a given day — even if she starts to lay eggs the next day — it indicates that something went wrong.
Curtsinger compares with a car that works running out of fuel. It can travel several kilometers, but the first glitch that points the driver in a hazardous situation.
Work Curtsinger also revealed something else that is not done by the analysis of Mueller and rose.
At the end of the phase of retirement, when the level of fertility is low and death is inevitable, it becomes clear that fly out on a plateau of mortality are the same as those associated with the stage “end of life”. “This is a completely new observation,” he says. Plateau of mortality is not a feature of old age, it can appear in the middle or at a young age.”
The General consensus currently is that a plateau of mortality associated with age — but Curtsinger finds that his new job shows that they — like death itself — may be more associated with fertility. This observation may require biologists to revise their theories of aging.
Something, however, puzzling Curtsinger. Why there is this strong connection between fertility and death? Explanations from biologists there.
However, James Carey of the University of California, Davis, believes that all this simply reflects the well-studied idea: reproduction is the cost of the health of parents, especially mothers. Women face the problems of teeth, for example, as a consequence of having many children.
Over ten years ago, Carey and his colleagues showed that the modification of the reproduction system of mice also alters their time of life. They put the old mice on the operating table and replaced them with spent ovaries equivalent bodies of more young females and old mice lived longer than expected after surgery.
“There were signs that the mice that received new ovaries, had fewer heart problems than mice who new ovarian not received,” he says.
Kurtsinger not agree that people pass through a stage of “retirement” before his death, but Mueller believes that there is evidence that people, doomed to death by natural causes, are experiencing a death spiral. Confirmation that Mueller cites another study conducted in Denmark in a nursing home.
The researchers had a group of ninety volunteers through a battery of tests to assess their strength, coordination and mental abilities. After a few years they returned to the nursing home to find out who died and who still lives. The people who died, for the most part bad passed the tests, says Mueller. At the time of death had a decline in physical capabilities.
More interested in what a scientist is the fact that fruit flies can identify strategies to prevent this cycle of death that was begun a few days, not weeks.
It is hoped that this work may give new hints on how to save people from a long and slow decay before death. It would be interesting to reduce the spiral of death that you were as healthy as the other, until you die.
So even though Mueller and rose I think I have found the fourth stage of life, in the long term, they hope people can get out of it or at least reduce as much as possible.