Long-lived worms can transmit their extended lifespan to the next generation by passing on changes in the way their genes are used, rather than differences in DNA itself.

A study has shown that nematode worms can inherit a "memory of longevity" from their parents, even though their genome remains unchanged.

It is not clear if the same processes apply to humans, but Anne Brunet from Stanford University, who led the study, noted that some genes that affect the lifespan of nematodes were later found to influence human longevity too. "In several cases, the worm has proved to be a good model for humans, who live 2,000 times longer," she said.

Her team is now looking to see if the results in the worm Caenorhabditis elegans translate to species that are evolutionarily closer to humans, such as fish and mice.

The discovery is an example of "epigenetic inheritance", where organisms pass on changes in the way genes are used rather than in the genes themselves. As animals develop, their DNA and proteins become annotated by molecular marks that act like Post-It notes, dictating which genes are read without changing the underlying text. The marks are meant to be stripped away with each new generation, but some stay behind.

Brunet says her study and others show that epigenetic inheritance has broad implications for complex traits like longevity, or possibly even diseases like Alzheimer's, cancer and diabetes. "These have very different causes, including genetic factors and what we do to ourselves. But maybe we're missing a component: what our parents and grandparents have done," she says.

Studies like this could help to improve techniques such as cloning or reprogramming cells to become stem cells, which depend on correctly erasing or maintaining epigenetic marks. Eventually, scientists may even be able to manipulate these marks to boost lifespan or reduce the risk of diseases that pass from one generation to the next.

The latest discovery, published on Wednesday in the journal Nature, began when Brunet's student Eric Greer was working with worms that had mutations in one of three genes – ASH-2, WDR-5 and SET-2. This trio controls how DNA is packaged, converting it from a tightly packed form into a loose, open one where genes can be more easily read.

If any one of the trinity of genes is faulty, various stretches of DNA close up. This restricts access to several genes, including some that are involved in ageing. As a result, the worms live around 20-30% longer.

Greer bred the mutant worms so some of their offspring had working copies of all three genes. But even though their genes were normal, they still lived longer than usual, a trend that continued for three generations.

In recent years, scientists have found several examples of epigenetic inheritance, in everything from the symmetry of flowers to the hair colour of mice. But, said Brunet, "We didn't expect that a complex trait like longevity could be inherited in a non-genetic manner."

"It is beautiful work," said Prof Emma Whitelaw from the University of Adelaide. "Transgenerational epigenetic inheritance is an area of much controversy, and it is difficult to rule out undetected genetic differences."

In Greer's study, the fact that the long life disappears after three generations makes it very unlikely that genetic changes are involved. "This will stimulate researchers to take the notion more seriously," said Whitelaw.

Epigenetic inheritance is often portrayed as a revolution in evolution. It seems to hark back to the discredited ideas of Jean-Baptiste Lamarck, who suggested that traits acquired by parents would be transmitted across the generations.

"The discovery that epigenetic changes can carry across generations has made people realise that not everything is written in the genes," said Brunet. "That's not to say that Lamarck was right, but we now understand that there's epigenetic memory for some traits."

Dr Bas Heijmans from Leiden University Medical Center stressed that epigenetic inheritance "is by no means contradictory to the modern view of evolution … Natural selection will have allowed epigenetic inheritance to evolve if it increased Darwinian fitness."

Epigenetic inheritance could give organisms a short-term advantage, by giving the next generation advance notice of the challenges that the current one is facing. "If there's a famine, it might be advantageous to have this information passed on," said Brunet.

The long-term consequences of this are not clear. The long life of Greer's worms, like most other examples of epigenetic inheritance, disappears after a few generations. They are unlikely to have a lasting impact on the fate of the species. "It's not a long-term evolutionary thing," said Brunet.