Humans live much longer than chimps due to a slower epigenetic ‘clock’

Breakthrough advances in medicine and better nutrition have dramatically improved the longevity of the average human over the past two centuries. But that’s not to say that some couldn’t go on to live a long life even before the advent of modern medicine. As long as they were spared by disease, wars, and other risks that can bring an untimely death, humans could live to see their 70s, 80s, and even reach 100 years old as far back as ancient Rome.

The longevity of humans is somewhat exceptional among primates. Chimpanzees, our closest living relatives, rarely make it past age 50, despite them sharing over 99% of our DNA. In a new study, researchers think they’ve found our secret: chemical changes along our genome that occurred around 7-8 million years ago when our ancestors branched away from the lineage of chimps.

Slower ticker

There are tens of thousands of genes in the human genome, but that doesn’t mean all of them are active. For instance, through the methylation of DNA across certain sites of the genetic sequence, genes are locked in the “off” position. These modifications, known as epigenetic changes (‘epi’ means ‘above’ in Greek), do not alter the DNA sequence itself but, rather, simply regulate the activity of genes.

DNA methylation involves attaching small molecules called methyl groups, each consisting of one carbon atom and three hydrogen atoms, to segments of DNA. When DNA gains or loses a methyl tag, such events mark time. In fact, the changes are so consistent that methylation can be used as an “aging clock”. Previously, scientists were able to estimate a person’s chronological age based on their gene activity within less than four years.

In a new study, researchers at Duke University and George Washington University have analyzed age-related epigenetic changes in chimpanzees. They analyzed over 850,000 methylation sites in blood from 83 chimpanzees aged 1 to 59.

Just like in humans, aging also leaves its epigenetic signature on the genomes of chimps, the authors of the study found. More than 65,000 DNA sites changed in a clock-like fashion across the primates’ lifespan, some gaining methylation and others losing it.

The DNA methylation pattern was so reliable that the researchers could tell a chimp’s age from their genomes with an error within 2.5 years — much more accurate than other methods, such as estimating an animal’s age by measuring the amount of wear on their molars.

When compared to the epigenetic aging clock of humans, the researchers found that a chimp’s clock ticked faster. The authors aren’t sure that these changes actively contribute to aging or merely track the aging process. However, they hope they might eventually learn more about how gene regulation could be involved in physical and cognitive decline that often accompanies aging.

The findings appeared in the Philosophical Transactions of the Royal Society B.

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