Last October, a study published in the journal Nature concluded that the upper limit of human age seems to be stuck at about 115 years. But now a rival group of researchers have presented evidence of the opposite - that there is no detectable limit to human lifespan.
The lives of the oldest human beings have fascinated researchers for many centuries, but it's only in recent decades that we've been able to start to analyse the genetic basis for extraordinary lifespans.
Now, a team of McGill University biologists led by Bryan G. Hughes and Siegfried Hekimi have analysed the lifespans of the longest-living individuals in four different countries - the USA, the UK, France and Japan - for each year since 1968.
The conclusion of their research is that there is no evidence of any hard limit to human lifespan. If one exists, it has yet to be reached or identified. "We just don't know what the age limit might be. In fact, by extending trend lines, we can show that maximum and average lifespans, could continue to increase far into the foreseeable future," Hekimi said.
Technology, medicine and living conditions
Average lifespans have been shown to rise alongside per capita income - a fact illustrated beautifully by statistician Hans Rosling in the video below - and it seems that maximum lifespan seems to follow the same trend, says Hekimi. Technology, medicine and improvements in living conditions could all increase the upper limit.
"It's hard to guess," Hekimi adds.
"Three hundred years ago, many people lived only short lives. If we would have told them that one day most humans might live up to 100, they would have said we were crazy."