We are all familiar with the phases of life, even if we don’t explicitly know it. First comes childhood, with all its associated development and growth, followed by the longest phase of adulthood. This can, obviously, last decades, and is associated with an exponential chance of death as people get older. This then leads to a third phase of life, known as “late life”, in which paradoxically the chances of dying plateau, before people eventually kick the bucket.
But some research suggests that rather than being limited to just three phases of life, there may be a fourth, reports the BBC. By studying how fruit flies age, researchers claim that they have discovered what they are calling the “death spiral”, which they say has enabled them to predict with an 80 percent accuracy when a fly might die. In another twist, they even hint that this phase might be found in humans too, though others have been slightly more skeptical about this.
It was back in the 1990s that the late life phase was first discovered. Scientists noticed that while the chances of death by natural causes steadily increased as people got older, when people reached extreme old age, this relationship no longer held. A 90-year-old, they found, had the same chances of death as a 100-year-old. This leveling off in the pattern of mortality was a bit of a shock to the researchers, and it is still not really understood what it is that causes it.
Yet it was this mystery that led to the discovery of another. While investigating the late life phase of fruit flies, often used by biologists as model organisms due to their quick generation time and vast understandings of their genetics and biology, a different group of researchers found another oddity. They discovered that regardless of a female fly’s age, in the two weeks leading up to their death, their fertility dropped. Soon this was also found to be the case with the male fly’s fertility, too. It could be to do with the fact that producing eggs for a female fly is costly, and if they are about to die they may give up on it.
This fall in fertility is what the researchers dubbed their “death spiral”, and by looking at how individual female fly’s fertility dropped over a period of three days, they were able to – to a limited degree – predict when they might die. This link between fertility and death has been backed up by other studies from separate researchers, though there are doubts as to exactly how applicable this is to humans.