Human life expectancy has increased so much over the last four generations that 72 can be considered “the new 30”, according to a study led by researchers from Germany.
The study, published today in US journal PNAS, found that mortality at younger ages is now 200 times lower than that of previous generations, with the bulk of mortality reduction occurring since 1900.
The study used already published data to make comparisons between human populations (past and present), and other species, said Susan Lawler, head of LaTrobe University’s Department of Environmental Management & Ecology.
The findings reveal that hunter gatherers at age 30 have the same probability of dying as Japanese individuals at age 72, with the average mortality of hunter gatherers nearer to chimpanzees than to humans in some industrialised countries.
By comparing the longevity of humans with that of other species, including fruit flies, the researchers make the case that the drop in mortality stems not from modifications to genes, but from the environment.
“We have therefore prolonged human life by altering our environment rather than by adapting to the environment,” Dr Lawler said.
But life expectancy still remains a challenge for some populations, with the study finding a large variation between the highest and lowest mortality populations.
The worst case was 19th century slaves on Trinidad, who suffered death rates at all ages that were higher than those for hunter gatherers.
The authors note that we observe more variation among human populations that we see between species, Dr Lawler said.
“If our mortality in Sweden 100 years ago was not very different to that of hunter gatherers, it is obvious that the rate of change is not evolutionary (however revolutionary), and there are certainly some modern human populations whose life spans remain low. Check the data on modern aboriginal people, and weep.”
The study delivers a novel and quirky comparison of data said Rob Brooks director of the Evolution & Ecology Research Centre at University of New South Wales.
“It makes sense that there’s been not just a prolonging of life but a putting off of that increase in mortality rates,” Dr Brooks said.
He added that genetics and environmental issues interacted with one another, meaning genetics were still important to the discussion, with the genes that are killing us now not the genes that killed hunter gatherers.
“Now the genes that are killing us are the ones that kick in our 30s and 40s and especially 80s and 90s – cancer and dementia.”