HOW ONE HUNDRED BECAME THE NEW NINETY

THE FIRST CENTENARIANS Perls recruited to his study were born around 1900, when the average life expectancy was about 46 – achingly low, mainly because infant mortality was tragically high. Families could count on losing about a quarter of their children, mostly to infectious diseases, says Perls.

But with improvements to public health – clean water, sanitation, education, better nutrition – and the advent of vaccines and antibiotics, an otherwise doomed quarter of the Greatest Generation not only had a chance to survive infancy and thrive, but also to age.

They lived through the Depression

and the Second World War and, as they matured, so did medicine. Screening for early signs of heart disease and cancers, the western world’s big killers, became routine, as did new preventive treatments, such as drugs for high blood pressure, and surgical interventions.

Another boost to longevity came in the late 1970s and early ’80s, says Perls, as the lethal perils of smoking became widely known and more people kicked the habit. With a broader understanding of behaviours that could be bad for the heart, more people started exercising and improving their diets.

For Perls, these factors explain how the prevalence of centenarians in North America has jumped from one in 10,000 people to about one in 5,000. He suspects it will rise further as baby boomers reach their 10th decade, but by how much is unclear. The factors that might predict a century-long life are varied and mysterious.