"In terms of the probability you'll live through the year, it's astronomical the improvement that we've made," said Oskar Burger, an evolutionary anthropologist at the Max Planck Institute for Demographic Research, Germany.
"The probability that you'll live through the year in our evolutionary past that was experienced at age 30 or even 20 is now typical of people who are 70.
"Seventy-two is the new 30," he said.
According to a 2002 study, life expectancy at birth has been increasing steadily at a rate of three months each year since 1840. That's a remarkable pattern, says Burger, especially for a trait that is so complicated and dependent on so many variables.
Burger and colleagues wanted to get a deeper, more evolutionary perspective in order to better understand the underlying biology of what determines how long we live.
They began by gathering results from a study published in 2007 that compiled the life-expectancy patterns of several well-studied hunter-gatherer populations, the 'Discovery News' reported.
They compared those numbers with data from Sweden and Japan, where people today are born with some of the longest life expectancies in the world.
Researchers compared populations of hunter-gatherers who live like our ancestors did and rely exclusively on their own foraging skills, to those that have some access to Western clothing, food and medicine experience a big boost in survival.
For developed nations, improvements have been even more dramatic, with the biggest gains in infant mortality. For today's babies in the longest-lived places, the chances of surviving are 200 to 300-fold better than for people born into conditions like those our ancestors faced.
The scale of improvement drops in later decades, but the differences are still significant.
A 65-year old hunter-gatherer has about a 5 per cent chance of dying over the next year, for example, compared to a less than 1 per cent chance of death for a 65-year-old person living in Japan.
Through age 15, hunter-gatherers experience rates of death more than 100 times higher than do today's Japanese. Over the course of the entire lifespan, mortality rates are 10 times higher.
The study findings appear in the journal Proceedings of the National Academy of Sciences.
