There are some stories that stay with you forever, the big scientific moments that change the course of history. These are not those moments – but we can’t stop thinking about them anyway.

Push my button

Surgeon Stuart Meloy was performing a pain-relief operation on a woman’s spine when she started exclaiming emphatically. “You’re going to have to teach my husband to do that,” the woman said. This inspired Meloy to invent an implant to help women who are unable to achieve orgasms in the usual way. New Scientist broke the news in 2001, sparking a frenzy of worldwide media excitement. But 13 years later, Meloy was still struggling to raise funds for a full clinical trial, and the “orgasmatron” never reached a climax.

Monkey pleasure

We aren’t the only primates capable of coming up with creative ways to pleasure ourselves. In a study of long-tailed macaques (Macaca fascicularis) in Bali, Indonesia, at the University of Lethbridge in Alberta, Canada, and her colleagues filmed hundreds of examples of male and female monkeys using stone tools as sex toys, rubbing or tapping them on their genitals. According to at the University of Western Australia, the Balinese monkeys get plenty of food handouts from humans, and this frees up time for sexual experimentation. But some monkeys in other places have unusual kinks, too: another study reported a wild macaque in Japan rubbing its genitals on the back of a sika deer.

Head transplants

In 2015, surgeon Sergio Canavero announced plans to carry out the first human head transplant, intended to extend the lives of people with muscle and nerve degeneration or widespread cancer. He claimed his technique could overcome technical hurdles, including how to fuse the spinal cord and prevent the body’s immune system from rejecting the head. In the following two years, Canavero published animal experiments supposedly backing up his methods, but other surgeons remained highly sceptical. A human head transplant never did happen, but Canavero has reportedly moved on to an even bolder ambition:

Rats driving

Have you ever wondered if a rat can drive a car? Kelly Lambert at the University of Richmond in Virginia has. She and her colleagues built a tiny car with three copper bars that would steer it left, forward or right. Sure enough, 18 rats learned to drive towards food rewards. They even found it relaxing, as measurements of their stress hormones indicated. Lambert proposed that driving challenges could replace traditional maze tests when using rat models to study neuropsychiatric conditions.

The sniff test

Humans are more similar to rats than we like to think. In a psychology experiment, and his colleagues at the Weizmann Institute of Science in Rehovot, Israel, surreptitiously filmed 153 volunteers. After shaking hands with someone of the same sex, people smelled their shaking hand more than twice as much as they did before the handshake. Puzzlingly, after shaking hands with someone of the opposite sex, people were more likely to sniff their non-shaking hand. The team suspected that humans use chemical signals all the time without being aware of it.

Urine fountains

Communication through scent is, of course, widespread in mammals, but some never-before-seen behaviour in dolphins took biologists by surprise in 2025. While studying Amazon river dolphins (Inia geoffrensis), or botos, in Brazil, Claryana Araújo-Wang at CetAsia Research Group in Ontario, Canada, saw a male “flip his belly up out of the water, expose his penis and then proceed to urinate into the air”, she told New Scientist. They saw dolphins do this a total of 36 times, and most of the time another male was nearby and would pursue the stream of urine. The purpose of this behaviour hasn’t yet been established, but hormones in urine might signal a male’s social position or physical condition, said Araújo-Wang.

Giving the finger

As for human modes of communication, many of us struggle to put our smartphones down – so the last thing we’d want is for them to crawl across the table towards us. Nevertheless, Marc Teyssier at the University of Paris-Saclay in France and his colleagues gave phones this ability in 2018, with a robotic appendage dubbed the MobiLimb. It plugs into a device’s USB port and, for some reason, looks eerily like a human finger, giving it a spooky quality reminiscent of Thing from The Addams Family. The MobiLimb can stroke your wrist, wave, wag like a tail or, most disconcertingly, drag the phone around. Thankfully, the idea hasn’t taken off.

Horror frog

If you find the thought of a phone with a finger horrifying, wait until you hear about the nightmare-inducing hairy frog Trichobatrachus robustus. In 2008, researchers reported that these frogs can break their own bones to produce claws that burst through their skin. at Harvard University’s thought these weapons were for defence, but two years later, that they were used in fights between males – and that the frog’s unusual hairs were a kind of armour to protect its vulnerable parts from sharp claws.

Corpse shrinking

In 1957, when New Scientist was 1 year old, we reported on a new method for shrinking an adult human body to the size of a baby. At an exhibition of inventors in Winnipeg, Canada, the unnamed inventor of this process claimed it would make disposing of dead bodies simpler, as they could be slid into underground tubes and take up less space. The method involved applying high pressure to the corpse and squeezing out fluids so its flesh could be compressed into a mould. “All this is, of course, highly ingenious but it is uncertain why the inventor thinks that his newly proposed form of burial is in any way better than the current and very popular method of cremation,” the writer mused.

Transient anus

We may take it for granted, but the anus, which allows food to pass through the body, was an evolutionary breakthrough, both figuratively and literally. The earliest animals, like jellyfish today, had only one gut opening, where food went in and waste came out. In 2019, scientists discovered that the warty comb jelly (Mnemiopsis leidyi, pictured top) forms an anal opening when it needs to defecate, but it vanishes straight afterwards. This, they suggested, could represent how the anus evolved in the first place.

Fart science

Flatus – gas expelled from the anus – has been a topic of endless fascination for many readers (and journalists). In 2001, we featured the work of Michael Levitt at the Veterans Administration Medical Center in Minneapolis, a leading authority on the subject. He developed a “Toot Trapper” that reduces odours by trapping certain gases using activated charcoal. We also reported on a device for monitoring gas emissions from dogs, used to test dog snacks that were supposed to reduce flatulence. In 2016, researchers in Australia worked out which foods cause the smelliest farts by mixing faeces with different foods. They recommended eating less protein and more slow-release carbohydrates to minimise hydrogen sulphide production. In 2022, at the Mayo Clinic in Rochester, Minnesota, and his colleagues worked out that some poos float because of gas from gut microbes, confirming a hypothesis first put forward by Levitt 50 years earlier.

Brew your own

Even stranger things go on inside some people’s intestines, as we found out in 2019. A 46-year-old man started experiencing unexplained mental fogginess, dizziness and memory loss, and had to give up his job. Later, doctors found high levels of alcohol in his blood when he hadn’t been drinking. Eventually, they realised his gut contained high levels of Saccharomyces cerevisiae – brewer’s yeast – which got him drunk any time he ate a lot of carbohydrates. This rare condition, known as auto brewery syndrome, had been triggered when the man took antibiotics for a thumb injury, which disrupted his gut microbiome. This year, a study reported that another man with this condition fully recovered after getting a transplant of faeces from a healthy donor. Both articles were written by Alice Klein, who we also have to thank for the monkey sex toys, car-driving rats, smelly farts and floating poos. Thanks, Alice!

It is the year 2036. A patient struggling with depression and anxiety is referred to her local psychobiotics clinic where the consultant prescribes a course of personalised pills to improve her symptoms. But rather than acting on her own cells, let alone those in her brain, the pills work by administering specific strains of microbes in her gut.

This future vision of doctors tweaking the contents of your digestive tract to improve complex and hard-to-treat psychological disorders might seem far-fetched. But research over the past couple of decades has revealed the far-reaching impact of the ecosystem of bacteria, fungi, viruses and other microbes that lives within us. Perhaps most surprising has been the associations scientists have discovered between the gut microbiome and our mental health. Now they are exploring whether harnessing this intricate ecosystem could help people feel better.

Growing evidence

The notion that your “gut feeling” connects with your psychological experience of the world is well established in popular imagination. But until recently, scientists were deeply sceptical—particularly of the notion that the multitude of microbial cells inside us could have an impact on mental health. “Fifteen years ago, there was sniggering at the back of the seminar room when people presented their research,” says Professor Phil Burnet, a neuroscientist at the University of Oxford, UK.

But the field of microbial neuroscience has accelerated rapidly over the past decade, thanks to an explosion of lab studies and trials in humans that involve microbiota. Some explore live beneficial microbes known as probiotics, others formulations of microbe food, or prebiotics, to fertilise specific bacterial strains. Meanwhile, heat-treated microbes, or postbiotics, are also being developed.

Together, these studies paint a picture of deep and important connections between the — from as many as 5000 different species — in your digestive tract and your physical and mental health. “How can we use this to maintain wellbeing or treat brain disorders?” asks Burnet. “Within the gut-brain circuit, the gut microbiome is the most accessible component.”

What happens in vagus

The neurons that operate the gut are sometimes referred to as our “second brain”. Known as the enteric nervous system, in humans it contains an estimated 500 million neurons, more than . It operates autonomously to control digestion but is also in constant bidirectional communication with the brain via the vagus nerve.

This second brain and its connection with the one inside your skull is one way that gut microbes can affect mental health. There are others too: via metabolites they produce passing into the blood and crossing the blood-brain barrier, by impacting gut hormones and by stimulating the immune system.

“The microbiome is endlessly complicated, and what I suspect is that there is more than one mechanism for the clinical effects that we see,” says Dr Richard Day, V.P. Medical Affairs and Clinical Development within R&D at ADM, a company that researches and markets pre-, pro-, and postbiotics. “We’re still on that journey to unpick the mechanisms of action.”

The fact that the gut microbiome is capable of impacting the brain is, however, clear.

Some of the strongest evidence comes from research into mood disorders, with studies showing associations with gut microbiome composition. Now, scientists are moving beyond these observational studies to experimental interventions to find out more.

A mechanistic study led by the University of Oxford, for example, found that giving participants a probiotic had measurable effects on their cognitive and emotional processing.  Other studies are exploring the gut-brain axis in clinical populations. In 2023, for example, researchers at King’s College London and ADM published a study in JAMA Psychiatry, exploring the effects of a probiotic in people with major depression. “Together, these studies paint an increasingly compelling picture of the gut-brain connection,” says Dr Malwina Naghibi, Head of Clinical Development at ADM.

A two-way street

This connection works both ways: mental health can affect digestive health and vice versa. Irritable bowel syndrome (IBS), for example, has an established relationship with anxiety, and this link is being actively explored. In , ADM’s researchers gave adults with IBS either a live or a heat-treated strain of gut bacteria. Both produced similar results in patients, providing researchers with vital clues on how bacteria—alive or dead—interact with the gut and nervous system (see Box, right).

scientists are relishing the challenge of exploring this new frontier

These studies are typical of a proliferation of mostly small, but rigorous clinical trials testing the impact of the gut microbiome on , (ADHD) and . There is even into whether it plays a role in Alzheimer’s disease.

What’s needed now are larger studies over longer periods that can show how robust any impacts really are. “There is just this explosion of research at the moment,” says Naghibi.

The sniggering at the back of seminar rooms has gone quiet, but there is still a long way to go. Microbial neuroscience is a field in its infancy, psychobiotics even more so. Yet scientists are relishing the challenge of exploring this new frontier. “I think this is the most exciting part,” says Naghibi.

MICROBIAL AFTERLIVES—THE SCIENCE OF POSTBIOTICS

The new kid on the block in microbiome research is postbiotics. Unlike probiotics (live microbes) or prebiotics (microbe nutrients), these are preparations of microbes inactivated by heat or other methods, sometimes also together with the soup of cell fragments and metabolites they produce (see graphic). Even though the microbes are no longer alive, they can still exert biological effects. ADM scientists, for example, have shown that heat-treated bacteria produce to live ones in people who have IBS.

These effects can be rapid. A of postbiotics and the gut-brain axis noted physiological changes within an hour of administration. And findings from other trials suggest that the effects of postbiotics wear off when participants stop taking them. This suggests a direct effect rather than a permanent change to the microbiota, though much more research on mechanisms is needed.

Meanwhile, postbiotics are being investigated in a wide range of conditions. The ADM team, for example, has conducted a trial of 72 people exploring whether postbiotics can reduce the symptoms of allergic rhinitis.
The advantage of postbiotics over probiotics is that they don’t need to be kept alive, meaning they can be added to foods or drinks. Why swallow a pill if you could take postbiotics in the milk on your cereal? 

Learn more at:

Discarded sex hormones can be returned to the bloodstream by bacteria in the gut – and now, a study has found that there are far more of these sex-hormone-recycling bacteria in the guts of people in industrialised societies than in those of hunter-gatherers and non-industrial farmers. This might mean that, as a result of urban living, some people have higher blood levels of certain sex hormones, which would have profound health effects.

“We don’t how the body would respond to this increased input,” says Rebecca Brittain at Jagiellonian University Medical College in Poland. “But the implications could be quite large.”

Sex hormones, such as oestrogens, circulate in the blood. When levels are too high, cells in the liver add a chemical tag that results in a hormone being excreted, often via the gut. But that tag happens to be a sugar molecule that certain bacteria feed on. So, some bacteria in the gut cut off the tags, using enzymes called beta-glucuronidases.

Once a tag is removed, a hormone can be reabsorbed by the body and end up back in the bloodstream. Studies suggest that substantial proportions of excreted sex hormones are recycled by gut bacteria in this way.

In 2011, to describe all the gut bacteria that can alter oestrogens, and thus potentially affect blood levels in both sexes. Earlier this year, it was proposed that be used to describe the gut bacteria that can affect testosterone levels.

The latest study from Brittain’s team has compared the oestrobolomes of hundreds of people from 24 populations around the world, using data from previous studies in which their gut microbiomes were sequenced. These populations included, for example, hunter-gatherers in Botswana and Nepal, rural farmers in Venezuela and Nepal, and city dwellers in Philadelphia and Colorado.

Free newsletter

Sign up to 91ɫ��Ƭ Check

Sign up to newsletter

Specifically, Brittain’s team looked for genetic sequences coding for beta-glucuronidase enzymes, measuring the overall proportion of these sequences and their diversity. The results suggest that the oestrogen-recycling capacity of gut microbes in industrialised populations is up to seven times greater than in the hunter-gathering and rural farming populations, with twice the diversity too.

The team also found that there is up to three times the recycling capacity in babies who are fed formula than in those who are breastfed, with up to 11 times the diversity. People’s age, sex and BMI, however, made no difference to their oestrobolomes.

Brittain’s team and others are now trying to establish if the higher recycling capacity suggested by the gene sequences really does correspond with higher levels of oestrogen recycling and, most crucially, if this results in higher blood levels of the hormones. It could be, for instance, that people’s bodies can adjust hormone levels to partially or completely compensate for higher recycling.

But if some individuals do have higher blood levels of oestrogens throughout their lives because of their microbiomes, it could have a big impact on their fertility and health, increasing the risk of certain cancers, for instance. But in some cases, these effects could be beneficial. “The assumption is usually that higher oestrogen recycling is harmful,” says Brittain. “I don’t think that’s a fair assumption. For some people with really low oestrogen levels this could be a good thing.”

A better understanding of our hormones and sleep could improve both

The hormonal changes of puberty, the menstrual cycle and menopause can all affect our sleep, but there are also subtler ways that hormones and sleep interact

“It is an interesting study that adds to the growing evidence of the importance of the gut microbiome function in human health and development,” says at Wake Forest University School of Medicine in North Carolina, who is investigating the possible links between the microbiome and the risk of breast cancer.

But it does have limitations, she says, including the fact that all the industrialised populations were in the US. “Additional cohorts, perhaps from Europe, could have strengthened the industrial associations,” says Cook.

Brittain says that she and her colleagues will try to identify the lifestyle factors responsible for the differences they found. “We would love to know so much more about these individuals, but the data didn’t exist, so we’ll do our own study,” she says.