How long did Neanderthals live? Or woolly mammoths? The identification of genetic markers that predict the lifespan of living creatures allows us to trawl the DNA of extinct species for answers.
Despite what some online scams may tell you, your lifespan can't be predicted precisely unless a disease makes that very short indeed. However, studies have found the density of DNA methylation sites known as CpG sites has a statistical correlation with mammalian lifespan. Dr Benjamin Mayne of the CSIRO Indian Oceans Marine Research Center compared CpG density on 42 genes for 252 vertebrate species with a database of animal longevity. The correlation Mayne found is imperfect (R2=0.76, where 1.0 is an exact match) but a long way better than random chance, showing the relationship holds for fish, reptiles, and birds as well.
Applying the same measures to the genomes of those no longer with us, Mayne concludes in Scientific Reports that Neanderthals and Denisovans could expect to live to 38 if famine, disease, or a saber-toothed tiger didn't get them first. For comparison, chimpanzees live approximately 40 years in zoos, and it is thought to be similar in the wild, although the record is 55, suggesting higher is possible.
Mayne told IFLScience the value he found for Neanderthals and Denisovans is similar to estimates for early Homo Sapiens prior to the invention of modern medicine. Whether vaccines, antibiotics, and plumbing would have allowed extinct branches of humanity to live as long as we do today is a hard question to answer.
Cold temperatures are sometimes associated with much longer lifespans, but Mayne estimates adult woolly mammoths and straight-tusked elephants averaged about 60 years, five fewer than the African elephant.
The database Mayne drew on uses the average age of individuals who appear to survive to their full natural life. In many species, high infant mortality would produce much lower figures if these were included in calculations as we do for human life expectancy estimates.
Even the lifespans of rare or hard-to-find living species can be hard to calculate if they are both very long. Mayne also estimated Pinta Island tortoises (whose most famous member was Lonesome George) averaged about 120 years, while bowhead whales would expect to make it to 270 before whaling and ocean plastics.
The relationship between CpG density and long life might lead those obsessed with immortality to wonder if they could genetically engineer themselves to longer life. Besides the practical difficulties, Mayne told IFLScience: “This is only an association.” It's unclear whether optimal CpG density extends life, or if it is a product of some underlying factor.
The research could have a different practical value, however. Long-lived species need greater protection against over-harvesting, and this could improve quota settings.