Humans

Mosquitoes may pick up on the fragrances in body washesbrizmaker/iStockphoto/Getty Images
The body wash you use in the shower may react with your natural odour to make you more attractive to mosquitoes.
Mosquitoes use various methods to find a target for their next blood meal, such as detecting an animal’s body heat, odour and the carbon dioxide they emit.
To learn if the body wash we use may have an effect, Clément Vinauger at Virginia Polytechnic Institute and State University and his colleagues selected varieties from the brands Dial, Dove, Native and Simple Truth.Advertisement
First, they placed two strips of nylon on one of the forearms of four volunteers and wrapped that area in foil, to collect the participants’ natural odour.
Next, the researchers washed part of each participants’ other forearm with about 1 gram of one of the body washes for 10 seconds, before rinsing it with water for a further 10 seconds. They then similarly applied two strips of nylon and foil to these forearms, to collect the wash’s scent. The researchers repeated this with the three other body washes.
One hour after each sample was taken, they took two strips – one from each of the body wash-exposed areas and one from the body wash-free areas – for chemical analysis while the other body wash-free and body wash-exposed strips were put in separate cups.
The researchers placed these inside cages with 16 to 25 female Aedes aegypti mosquitoes, which can transmit yellow fever, that were free to visit either cup.
The Simple Truth body wash appeared to increase the attractiveness of all of the participants, measured by the number of times the mosquitoes landed on their body wash-exposed strips compared with their body wash-free strips. The Dove wash had a similar effect, but the increase in attractiveness was only pronounced for three of the participants.
Dial’s body wash similarly made the participants more attractive to mosquitoes, but to a lesser extent than Simple Truth’s or Dove’s.
In contrast, the mosquitoes tended to avoid the strips washed in the Native body wash, but displayed a particularly strong aversion towards one participant’s Native-washed strip.
This suggests the body washes’ fragrances and the participants’ individual odours combined to create a scent that was detectable to the mosquitoes.
“Our study highlights the importance of the interaction between the specific soap chemicals and the body odour of each person in determining whether a person would become more or less attractive to mosquitoes after applying soap to their skin,” says Vinauger.
The experiment’s chemical analysis suggests that the compounds benzaldehyde, benzyl benzoate and γ-nonalactone may repel mosquitoes.

The researchers are planning to repeat their study with a larger group of participants and more body washes, and will investigate how long a wash’s potential mosquito-attracting or mosquito-repelling effects last after it is washed off the skin.
“The discovery that personal care products may cause mosquitoes to be attracted or repelled by the user opens the door for developing user-friendly mosquito repellents,” says Walter Leal of the University of California, Davis.
“The chemicals in such products may not directly affect mosquito behaviour, but they may disrupt the specific ratio of human emissions that attract mosquitoes,” he says. “Regardless of the mechanism, reducing human-mosquito interactions mitigates the transmission of vector-borne diseases.”
New Scientist contacted the four body washes’ manufacturers for comment but received no reply prior to publication.

Topics:Mosquitoes/Hygiene More

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MORE than 2300 years ago, Aristotle argued that happiness was the highest good. Later, the US founding fathers considered its pursuit to be an unalienable human right. These days, you will find countless books promising to reveal the secrets of a happy life. But have millennia of philosophical and scientific enquiry taught us anything about how to achieve that?
First, let’s look at how people who study happiness measure it. One of the most common strategies is to ask people to rate statements such as “In most ways, my life is close to my ideal” and “If I could live my life over, I would change almost nothing”. These aim to capture someone’s overall satisfaction with life, rather than their mood on a specific day.
That makes sense, says Richard Layard, co-director of the Community Wellbeing Programme at the London School of Economics, because asking people to sum up their general contentment is often more practical than measuring their emotional state over an extended period. The other thing, says Layard, is that general contentment fits better with philosophical definitions of happiness as an overarching quality, as opposed to transient pleasures.
Using this kind of scale, psychologists have attempted to identify the specific ingredients that contribute to happiness. Contrary to the idea that “money can’t buy happiness”, income does play a role: it is easier to feel pleased with your lot when you don’t have to worry about bills and can treat yourself to luxuries.
We are also influenced by the riches of others – we are less happy if we know our neighbour is earning more than us. … More

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IMAGINE a child, running barefoot through a forest, and a broken glass bottle buried just beneath the soil. What’s worse: that a present-day child steps on the shards, or that a child in 100 years from now does?
This question, posed by philosopher Derek Parfit in the 1980s, was intended to clarify our moral obligations towards unborn generations. Knowingly risking harm to a future person, he argued, is just as bad whether it is today or in a century.
Parfit’s ideas inspired a branch of moral philosophy called longtermism. It rests on three premises: future people matter, there could be a lot of them and we have the power to make their lives better or worse. Ensuring the future goes well should therefore be a key moral priority of our time.
All of which seems reasonable, at first glance: it apparently promotes the universal values of stewardship, the duty to posterity and being a “good ancestor”. But longtermism has proven controversial, with some critics arguing that it is a “dangerous ideology” that permits or even encourages the suffering of people alive today.
Is that fair? To make up your own mind, the first thing you need to know is that longtermism comes in different flavours. Many of the most strident criticisms focus on the implications of “strong longtermism”, a variant introduced in a 2021 paper by the University of Oxford’s Hilary Greaves and William MacAskill, which says that it should be the top moral priority of our time.
This would have striking consequences for how money is spent in the real world. Indeed, it is already having an influence. … More

Wine drinkers have a lot of options when choosing their preferred varietyKlaus Vedfelt/Getty Images
Variations in our salivary proteins may explain why different people can like different wines. Researchers have linked the concentrations of two types of proteins to how intense wine drinkers find a wine’s notes, such as fruity or floral, and their preferences for the alcoholic drink.
A person’s wine preferences may at least partially come down to their cultural background, knowledge of the drink and individual taste. But Kate Howell at the University of Melbourne, Australia, and her colleagues … More

Claire Plumridge
PICTURE the scene: you are making a cup of tea for a friend who is on their way and won’t be arriving for a little while. But – disaster – you have already poured hot water onto a teabag! The question is, if you don’t want their tea to be too cold when they come to drink it, do you add the cold milk straight away or wait until your friend arrives?
Luckily, maths has the answer. When a hot object like a cup of tea is exposed to cooler air, it will cool down by losing heat. This is the … More

A pierced deer tooth discovered in Denisova cave in SiberiaMax Planck Institute for Evolutionary Anthropology
DNA that seeped into an elk tooth pendant about 25,000 years ago has yielded clues about the ancient woman who wore it.
The tooth, worn as a necklace bead, probably absorbed DNA from the person’s sweat as it lay against her chest and neck. Marie Soressi at Leiden University in the Netherlands and her colleagues were able to extract that DNA without damaging the tooth through a new process that took eight years to develop. The technique might reveal unprecedented details about the social customs and gender roles of ancient populations, says Soressi.
“For the first time, we can link an object to individuals,” she says. “So, for example, were bone needles made and used by only women, or also men? Were those bone-tipped spears made and used only by men, or also by women? With this new technique, we can finally start talking about that and investigating the roles of individuals according to their biological sex or their genetic identity and family relationships.”Advertisement
Scientists have often suspected that ancient tools, weapons, ornamental beads and other crafted artefacts contain DNA from the people who touched them. But getting DNA out of these objects typically means removing sections for analysis – causing permanent damage. “We absolutely didn’t want to do that,” says Soressi.
To see if DNA could be coaxed out of ancient artefacts without destroying them, Soressi and her colleagues tested numerous combinations of chemicals and heating regimes on 10 previously excavated artefacts from Palaeolithic caves in France. They found that placing them in a sodium phosphate solution and raising the temperature incrementally from 21°C to 90°C (70°F to 194°F) led to the release of relatively large amounts of human DNA with no damage to the specimens.
The team then tested the procedure on another 15 excavated bone specimens from one of the caves. Genetic sequencing revealed DNA from many different humans – probably the scientists and technicians who had worked with the artefacts across the years, says Soressi.
To avoid such modern DNA contamination, the researchers then tried their technique on four tooth pendants excavated by colleagues in Russia and Bulgaria who wore sterile gloves and face masks. Their analysis revealed mostly animal DNA that matched the species used to make the pendants.
One tooth pendant from Denisova cave in Russia, however, also contained human DNA fragments, primarily from a single individual. There was enough genetic material for the researchers to positively identify a female Homo sapiens, in addition to the elk (Cervus canadensis) that provided the tooth.
While the human might have rubbed her DNA into the pendant if she had crafted it, the large quantity of DNA recovered suggests she was the individual who wore it, says Soressi. “As a porous material, that tooth was likely soaking in sweat,” she says. “It worked like a sponge, pulling in that human DNA and trapping it there for 25,000 years.”
The DNA showed that the woman was closely related to an ancient tribe that, thus far, had only been found more than 1500 kilometres to the east.

Daniella Bar-Yosef Mayer at Tel-Aviv University, Israel, finds the paper “very exciting”, in part because it could help explain the purpose of ancient jewellery. For example, it might signal something about the identity of the wearer or their group, or their marital status, she says. “If we find them in different contexts on men, on women or children of this species or another species, or different age groups, that would give us some better clues about what they’re meant for.”
The technique might also help resolve long-running scientific debates about whether certain artefacts were made and worn by Homo sapiens or Neanderthals, she adds.
The study could open the door to DNA analyses of museum artefacts across the globe, says David Frayer at the University of Kansas. “Curators are often hesitant to allow their specimens to be damaged for DNA analysis, however small the extraction,” he says. “The absolute strength of this paper is that [their] procedure gets around that. If it can be extended to specimens cleaned long ago, this would represent a great leap forward for ancient DNA work.”

Topics:DNA/ancient humans More

Around 1 in 10 people are left-handedEva-Katalin/Getty Images
Fewer than 3 per cent of people in China report being left-handed, despite the global average being closer to 10 per cent. Researchers think the difference is probably due to a continuing cultural stigma against left-handedness, which is less of an issue elsewhere, rather than genetics.
Hugo Spiers at University College London and his colleagues are overseeing a long-running study that assesses people’s ability to navigate using the mobile phone game Sea Hero Quest.
As part of this research, more than 400,000 … More

Nataliia Suietska/shutterstock
I LIVED happily without a microwave for 10 years, but, since acquiring one when I moved house last year, I have come to appreciate what a useful gadget it is. I have also realised that much of what I thought I knew about microwaves wasn’t quite right.
Microwave ovens work using electromagnetic waves, also called microwaves, with wavelengths of 12 centimetres or so – much longer than visible light, but shorter than most radio waves. Microwaves create an oscillating magnetic field that puts certain molecules in a spin: namely, molecules like water, which have positively and negatively charged portions. Anything … More