In 2013, deep inside South Africa’s Rising Star cave system, scientists discovered the remains of Homo naledi, an ancient human species with a brain just one-third the size of ours. Yet some evidence suggests they may have intentionally placed their dead there. If true, this would push the birth of burial rituals back hundreds of thousands of years and challenge the idea that complex emotions like grief require big brains. Were these ancient humans performing funerals? Or are we reading too much into the evidence? This is the story of Homo naledi and a discovery that forces us to rethink what it truly means to be human.

People who experience long periods of intense grief after the death of a loved one seem to have a higher risk of dying within the next decade than those who come to terms with their loss more easily.

Numerous studies have linked bereavement to poor health outcomes, such as . But most of these only tracked the bereaved for a few years after their loss, says at the University of Zurich in Switzerland, who wasn’t involved in the latest research.

Now, at Aarhus University in Denmark and her colleagues have examined how grief is linked to mortality up to a decade later.

The researchers used a national registry to obtain information on people who were being treated for a terminal condition. They then recruited more than 1700 of these people’s loved ones, such as a parent or partner, to complete a series of surveys – taken before their death and six months and three years after. These asked the loved ones – who were aged 62, on average – questions, like whether they were trying to avoid reminders that the person was ill or dead.

The team found that 670 of the loved ones were persistently experiencing low levels of grief after the death, such as feeling slightly confused about their role in life, while 107 of them were persistently experiencing high levels of grief, such as overwhelmingly feeling this way. The remaining participants experienced either grief that declined or delayed grief that kicked in some time after their loss.

Next, the researchers analysed the loved ones’ medical records 10 years after their loss. The death rate in the high-grief group was 88 per cent greater than in the low-grief one.

Free newsletter

Sign up to Health Check

Sign up to newsletter

“There’s a saying that bereavement breaks hearts,” says Maercker. The findings support the idea that prolonged, intense grief puts a strain on the body, leading to earlier death, he says. It may also bring about lifestyle changes, as bereaved people might be more likely to .

Why excessive positivity is bad for your health and mental well-being

There are real benefits to a positive mindset, but the idea that we should always look on the bright side has gone too far. Research into toxic positivity can help restore balance

Only 17 per cent of the loved ones had been diagnosed with a medical condition at the start of the study, but Nielsen says this was more common among people in the high-grief group. Higher rates of pre-existing conditions may partly explain why members of this group were more likely to die during the follow-up period, she says. It is also possible that poor health may intensify grief, says Maercker.

Offering extra support to people experiencing severe, prolonged grief – regardless of whether they have a condition themselves – could save lives, he says.

Archaeologists are questioning whether a deep response to death is our sole preserve

When it comes to living a long life, it seems not all organs are created equal. żěè¶ĚĘÓƵs have found that having a youthful brain or immune system may be key – more so than having a slowly ageing heart or lungs.

We already knew that organs age at different rates, but it is unclear which ones have the biggest influence on lifespan, says at the Icahn School of Medicine at Mount Sinai in New York.

So, Oh and his colleagues analysed the levels of nearly 3000 proteins in blood samples collected from more than 44,000 people who enrolled in the UK Biobank study when they were between 40 and 70 years old.

Using genetic data from past studies, the team was able to build a picture of where these proteins were in the body, pinpointing dozens of proteins that are especially abundant in 11 areas: the immune system, heart, brain, liver, lungs, muscles, pancreas, kidneys, gut and fat tissue. The high levels of these proteins indicate they are important in the proper functioning of these organs and body systems.

Next, the team trained machine-learning models to guess how old the participants were based on data from about half of them, creating a separate model for each of the 11 parts of the body. While these estimations generally matched the participants’ ages fairly well, some models overestimated or underestimated it, supporting the idea that organs age at different rates, says Oh.

The researchers used the trained models to predict the organ and immune system ages of the remaining half of the participants, who were followed for an average of 11 years after their blood was sampled.

Free newsletter

Sign up to Health Check

Sign up to newsletter

Oh and his colleagues found that having one prematurely aged organ, or an aged immune system, was linked to a 1.5- to 3-fold increased risk of death during the follow-up period, with the risk rising alongside the number of aged areas.

For the most part, having organs like a heart or lungs that appeared to be substantially younger than expected wasn’t linked to a reduced risk of death during the study period. The exceptions were those with the most youthful brains or immune systems, whose risk of death was reduced by about 40 per cent – rising to 56 per cent if both of these parts of the body were particularly youthful.

“The brain and immune system coordinate a lot of other things around the body, so if those go wrong, it’s not too surprising they might have outsized effects on lifespan,” says at Columbia University in New York.

How to tell if your immune system is weak or strong

New blood tests can reveal whether your immune system is fighting fit by looking at the balance of different immune cells, but there may be a simpler way of gauging your immune health

But it is unlikely that protein markers perfectly reflect the ageing process, says Cohen. “We may have incomplete knowledge of what proteins really come from what organs, and the proteins from a given organ might be better represented in the blood than other organs; that could be why certain organs pop out as more important,” he says.

What’s more, the participants were mainly wealthy and of European ancestry, so further studies involving more ethnically and economically diverse people should verify the findings, says at King’s College London. Oh says the team is planning research that addresses this.

Even if the findings hold true, we don’t have ways to specifically reduce ageing of the brain and immune system, says Oh. However, identifying markers of brain and immune ageing could help to develop drugs that target these to boost longevity.