Without modern medicine chances are you'd be dead before 40, new research has found.
Scientists in Australia say the "natural" human lifespan is just 38 - the age Britney Spears is right now, and less than half the 81 years the average New Zealander can expect from the day they're born.
They figured this out by looking at DNA from 262 different species, and how long they're known to live. Using this data, they have been able to work out the lifespans of extinct species - including early humans such as Neandarthals and Denisovans.
"Using the known lifespans of 262 different vertebrate species, we were able to accurately predict lifespan from the density of DNA methylation occurring within 42 different genes," said Ben Mayne of Australia's CSIRO research institute.
"There are many genes linked to lifespan, but differences in the DNA sequences of those genes doesn't seem to explain differences in lifespan between different species.
"Instead, we think that the density of a special type of DNA change called DNA methylation, determines maximum natural lifespan in vertebrates. DNA methylation does not change a gene's sequence but helps control whether and when it is switched on."
Using this knowledge, they worked out that early modern humans - the same as us, anatomically - would have lived about 38 years. This is about the same as other early human species, such as Denisovans and Neandarthals.
"In the past 200 years, the average life expectancy of humans has more than doubled because of modern medicine and changes in lifestyle," the study said.
Other famous 38-year-olds include Meghan Markle, Alicia Keys and Chris Evans.
Chimpanzees - a close relative of ours that didn't figure out medicine - have a life expectancy of 39.7 years. The oldest on record lived to 55.
Woolly mammoths would have lived about 60 years, the scientists said, while bowhead whales could live to be 268, well beyond the lifespan of the current known record-holder.
The researchers said knowing how long different species live will help estimate extinction rates and sustainable yields in fisheries, as well as manage biosecurity risks.
"These genes are likely to be good targets for studying ageing, which is of huge biomedical and ecological significance," said Dr Mayne.
The research was published Friday in the journal Scientific Reports.
