Since 1900, the average life expectancy worldwide has increased more than double, thanks to better public health and hygiene, as well as better food supplies. However, a new study carried out with long-lived Italians indicates that we have not yet reached the peak of human longevity. "If there is a fixed biological limit, we are not close yet," said Elisabetta Barbi, a demographer at the University of Rome. Barbi and his colleagues published their research on June 28 in the journal Science. The current record for the longest human life expectancy was set twenty-one years ago, when Jeanne Calment, a French woman, died at the age of 122. No one has lived any longer since then, as far as scientists know. In 2016, a team of scientists from the Albert Einstein School of Medicine in the Bronx made the daring statement that Calment's case was more atypical than it seemed. They argued that humans had already reached a fixed limit of life expectancy, which was about 115 years, according to their calculations. Several critics lashed out against that investigation. "The data set was insufficient and the statistics showed serious failures," said Siegfried Hekimi, a biologist at McGill University. Anyone who studies the limits of longevity faces two major statistical challenges. There are not many people who live until advanced ages and people with that amount of years often lose track of how long they have actually lived. "At those ages, the problem is to be able to make sure that the age is real," Barbi explained. Barbi and his colleagues searched the records of Italy to find all the citizens who had reached the age of 105 between 2009 and 2015. To validate their ages, the researchers tracked their birth certificates. The team ended up collecting a database of 3 836 Italian seniors. The researchers located the death certificates of the subjects who died during the study period and determined the rates at which several age groups were dying. It has long been known that the mortality rate is somewhat high in childhood and decreases during the first years of life. He goes up again with the adults in his thirties and finally shoots up between the ages of 70 and 89. If the mortality rate continued to increase exponentially in the ages of extreme old age, then the duration of human life would have the type of limit proposed by the Einstein faculty team in 2016. Jeanne Calment set the current record for human life expectancy in 1997, when she died at the age of 122. According to what scientists know so far, no one has lived longer. However, that's not what Barbi and his colleagues discovered. They noticed that among the oldest Italians the mortality rate stops increasing: the curve suddenly flattens and stagnates forming a kind of plateau. Researchers also found that people born in later years have a slightly lower mortality rate when they reach 105 years of age. By Carl Zimmer The New York Times.