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The human population in the U.S. and Canada is getting older—meaning that the proportion of elderly people is growing year by year. By 2050, researchers have projected, a third of the population of these countries will be 60 years old and older. This could pose a strain on socioeconomic systems such as healthcare, retirement benefits, and social security.  

An international group of researchers publishing in the journal Nature has proposed a new measure of “old age.” Projections using the method indicate that the percentage of elderly North Americans in 2050 will only be about half as large as traditional projections say. This Human Bulletin explains how our ever-increasing life spans make “old age” a state that changes with the times.