Apple may have arrived late to the party, but with Watch it's brought a gun to a swordfight

It's arrived: Tim Cook's watch of many colours. Kay Nietfeld/EPA

While all eyes and ears were trained on news of its smartwatch, Apple also used its spring Keynote to introduce changes to Apple TV, revisions to its laptop lineup, and a new service that builds on the health monitoring aspects of smartwatches to perform data collection for medical research.

As one digital TV service after another launches many have been left wondering when HBO, whose television dramas are highly sought and widely watched properties, would play its hand. And here it is: a partnership with Apple that makes the entire HBO back catalogue available through the new HBO Go digital streaming service, available exclusively through Apple TV. So while the Apple TV hardware hasn’t been updated for years, the partnership with HBO (and a price drop to £59) is a nice reminder for those who may have overlooked it.

Apple has extended its reach into car dashboards with CarPlay, into home automation with HomeKit, and into health monitoring with HealthKit. Apple hopes that ResearchKit, a new open-source API and service, will form the foundation for apps that can collect health data from larger numbers of volunteers, increasing sample sizes and frequency of data collection, making the data more useful for researchers. Five apps have been developed so far, to investigate Parkinson’s Disease, asthma, diabetes and cardiovascular disease with research groups in leading hospitals. There is an emphasis on privacy, with the user controlling the degree of information that is being shared.

The Macbook Air finally gets updated to a retina display, a faster, more energy efficient processor, and a trackpad that can supply tactile feedback. It is lighter, thinner, has a re-engineered keyboard and somewhat controversially rolls many ports into just one: the USB-C standard port, which will handle HDMI video, external hard drives and other USB peripherals. Inevitably this is going to mean buying another set of cables.

The new Macbook Air with shiny retina screen. Kay Nietfeld/EPA

Watch my watch

In any other keynote this reveal would have been the main news item. But of course the main event was the watch. Seven months since Tim Cook first revealed the device, it’s been a long wait for more technical details. Opinion is still split on whether it will be a hard sell. With fewer people wearing watches anyway, the market is split between those who want a fitness tracker and those that want a beautiful luxury object. Is there a need for a device which essentially duplicates the functionality of a smartphone? Apple has to convince us that the watch offers more, in clear terms of where glancing at a watch is preferred to pulling out a phone.

Usually reserved to only one or two colours, this time Apple offers 20 different combinations of ways to customise the watch in size, colour, watch and strap material – probably a necessity in order to sell a device that by nature of being frequently visible is more fashion than function.

One watch to rule them (but in many colours). Martyn Landi/PA

The styling of the watch itself is reminiscent of the first iPhone, with three versions in two different sizes, 38mm or 42mm high: the cheapest Apple Sport at £299 with an aluminium body and plastic straps, the middle tier Apple Watch from £479 in stainless steel and wrist bands in leather, steel or plastic, and the gold Apple Watch Edition, which starts at £8,000 – perhaps more expensive even than the Apple Lisa from 1983, which sold at US$15,000 at the time. All the information, but smaller and nearer. Apple

Most of the functionality of the watch requires an iPhone within a few metres – maps, messages, Siri and other apps are relayed from the phone using WiFi or mobile data. Apple suggests that the battery will last 18 hours in a typical day.

Not first to market, but best?

Apple invests heavily in research and development to create new devices and interfaces that differentiate its products, at least, until competitors release their responses. Apple’s watch uses an Ion-X glass or Sapphire crystal screen which is pressure-sensitive to varying degrees. The side-mounted dial, which Apple terms a digital crown, enables scrolling and clicking, and a button below it jumps to frequent contacts. It has a “Taptic” engine which provides vibration feedback for certain apps, for example suggesting directions in Maps. The sensors on watch’s underside detect heartbeat and combine with the accelerometer to measure physical activity, something Apple is pitching as a major selling point.

Developers are already creating software that will extend their iPhone apps to interact with and be accessible from the watch, as Apple has with its Apple Pay contactless payment system. Miniature messages appear on the device in what Apple calls Glances, giving the impression of dealing with such messages quickly without the hassle of pulling out a phone.

From watches to smartwatches, with only a little relief. XKCD, CC BY-NC

Will it sell? In the past 18 months customers have bought 5m smartwatches or fitness bands, with Samsung flooding the market with many smartwatch devices, but with fitness bands accounting for the majority of sales. Current estimates suggest that Apple could sell more than 8m watches, eight times as many as its largest competitor.

While many of its features will appear in competitor’s smartwatches in the subsequent years, for the moment the eponymous watch is best in class. To sound a note of caution: like the first generation iPhone, the second generation device will probably be half as deep and run twice as long. You may be unfazed about the risks of being an early adopter, but if the idea of paying another few hundred pounds for the latest model next year isn’t appealing, it may be sensible to wait.

Impulse racing: take the pilots out and solar-powered aircraft get really exciting

From Abu Dhabi, Solar Impulse 2 will travel east to India, China, and across the Pacific. Solar Impulse

An aircraft with a 72-metre wing-span – larger than a Boeing 747 – yet weighing only 2.3 tonnes, the Solar Impulse 2 has set off from Abu Dhabi on an attempt to circumnavigate the globe powered only by the sun.

If the Swiss pilot-entrepreneurs Bertrand Piccard and André Borschberg, who take turns to fly the single-seat aircraft, achieve their objective it will be a remarkable achievement and demonstration of the possibilities of solar power.

A solar-powered aircraft is a huge challenge for which the aircraft’s design must be finely honed by the two key requirements of efficiency and mass. The aircraft is powered by 17,000 solar panels fitted to the wing’s upper surface which charge lithium-ion batteries in order to provide power to the four electric motors driving four-metre propellers.

Set a course for maximum efficiency

While the aircraft’s batteries will be fully charged at take-off, it’s essential that the solar panels can continuously provide the energy required to keep the aircraft airborne. This is complicated as the amount of energy that the panels can convert is dependent on the weather conditions, the angle of the sun in the sky, and of course whether it’s day or night. So with ideal conditions the solar panels must generate an energy surplus in order power the aircraft and keep the batteries charged in order to keep the aircraft airborne during less ideal conditions or nighttime hours. Simply put, Without direct sunlight to provide energy, the system has to be tuned for maximum energy conservation in order not to fall out of the sky.

Efficiency is therefore critical in ensuring that the aircraft can eke out every joule of stored energy: components such as the electric motors, at the heart of the system, must be extremely efficient, so that no watt of power is wasted. This can be achieved by selecting an optimum motor design built with the best materials. Key materials include very powerful permanent magnets, which enable the motor to produce the torque it needs to turn. Also the specialist electrical steels that form the core of the motor which are extremely thin and offer very low electrical losses.

Weight loss for aircraft

It also tends to be the case that a heavy electric motor is the most efficient – so weight management is a real problem for a project such as this. Every kilogramme of mass added to a motor must be carried into the air by the airframe. To carry a larger mass the airframe must be heavier and more sturdy which in turn means that the greater overall weight requires more energy to get airborne, demanding larger batteries which add additional weight – an unsustainable increasing spiral.

However, this can be made to work. Perhaps the most impressive example of this technology to date is the Zephyr solar-powered aircraft, developed by UK firm QinetiQ. Powered by motors developed at Newcastle University, in 2010 the pilotless Zephyr broke the record for the longest ever sustained flight of any aircraft, spending two weeks in the air.

Aircraft not just for travel

Zephyr was never designed to carry a pilot, but instead act as a replacement for satellites. Fleets of aircraft such as these could stay aloft indefinitely at altitudes of 50,000-70,000ft, beyond the reach of commercial airliners. They could offer all the communications and relay services currently provided by satellites but at a fraction of the cost required to build a space-worthy vehicle and carry it into orbit.

Being closer to Earth – flying at altitudes of 25km compared to 36,000km for a geostationary satellite – generates lower losses in communication signals. This offers the possibility of low-cost, extremely high-speed communications, with no need for satellite dishes and large transmitters, and without the need for expensive infrastructure such as mobile phone towers and fibre-optic cables.

Looking at it from this perspective, perhaps the biggest weakness of Solar Impulse 2 is the project’s goal of carrying two people around the world. The human crew are heavy and they need to sleep, eat and drink. They are the limiting factors, not the aircraft’s technology.

While the conversion efficiency of solar panels is steadily improving, and their cost has plunged in recent years, the idea of solar-powered replacements for our fleets of airliners is perhaps fantasy. But the prospect of autonomous, pilotless aircraft with limitless range presents all sorts of opportunities and possibilities for the future.

Quantum weirdness passes the atomic walk test

Confused? You will be. Inga Nielsen/Shutterstock

Quantum mechanics is a funny beast. On one hand it is a hugely successful theory, providing predictions of unrivalled accuracy across the natural world. On the other, it is a theory famed for its weirdness and failure to make sense in everyday terms: under quantum mechanics, light is both a particle and a wave, cats can be both dead and alive, and objects at the opposite ends of the galaxy exert a “spooky action-at-a-distance” on one another.

But is this weirdness really necessary? Could there be a theory more fundamental than quantum mechanics and yet in which only sensible, “non-weird” rules apply?

In particular, if we could find a theory that was “realistic”, that is, based on an intuitive reality in which objects have well-defined properties – for example dead or alive, but not both at the same time – we would solve a whole host of quantum-mechanical headaches in one swoop. But is a realistic description of nature possible? Can we have a theory which does the same job as quantum theory, and yet is free from all its weirdness?

Concrete tests

A key contribution to this discussion came from John Bell in 1960s. In addition to realism, Bell considered theories with a second very natural constraint – locality. Locality is the notion that far-apart objects cannot influence one another instantaneously. Newton described its opposite, non-locality, as “so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it”.

Bell proposed an experiment involving two particles far removed from one another. He proved that, according to all local realistic theories, a certain sequence of measurements on the two particles always return results that, when added together, give a number less than or equal to one. This relationship is known as a Bell’s inequality. Furthermore, Bell predicted that under quantum mechanics, the exact same sequence of measurements can give a value that exceeds one.

Here then was a concrete, testable difference between quantum mechanics and the whole class of theories built on local realism.

Since the initial work of John Clauser and Alain Aspect, this difference has been experimentally tested – with increasingly large distances between the particles. The result is clear: actual measurements of Bell’s ideas give a value higher than one. As this is beyond the realm of possibilities with local realistic theories, such theories cannot be viable descriptions of nature.

Doing the quantum walk

Bell’s tests involve multiple, separated objects and rule out theories which are both realistic and local. But for a single object, locality (its distance from another) isn’t an issue. So could it be that realism and realistic theories can still help us out of quantum paradoxes involving only single objects, such as Schrödinger’s cat?

This is the question addressed in new experiments by my colleagues at the University of Bonn. The team, led by Andrea Alberti, used lasers to first trap a single caesium atom and then drag it back and forth in a sequence of steps known as a “quantum walk”.

An atom takes a quantum walk through many paths at once. Robens et al. Phys. Rev. X 5, 011003, CC BY

Under a realistic description of its motion, the atom has a well-defined position at every point in time, even when we are not looking at it. Provided that we also assume it’s possible to measure the atom’s position without disturbing it, this property leads to another testable inequality – the Leggett-Garg inequality.

By looking for where the atom is not, rather than where it is, the Bonn team were able to perform the most faithful Leggett-Garg test to date. Their results show a clear victory for quantum mechanics – contrary to realistic theories and our own intuition, the quantum-walking atom has to be considered as being in two places at the same time.

A quantum future

Taken together, results like these make the hope of replacing quantum mechanics with something more “sensible” appear futile. By insisting that our new theory be realistic, we inevitably end up with weird results that include the ability to act on distant objects or measurements that disrupt what they are trying to record. And these make our new theory at least as weird, if not weirder, than the quantum theory we are trying to replace.

But rather than feel disappointed at losing our easy way out from quantum’s difficulties, we should feel emboldened in our confidence in quantum mechanics. The measured violations of Bell and Leggett-Garg inequalities stem from the quantum-mechanical properties of entanglement and superposition, respectively. By embracing these properties, we are learning to construct new technologies such as quantum computing, quantum imaging and quantum encryption.

More fundamentally, future research will extend these quantum tests to include ever larger objects. We are confident that quantum mechanics holds at the smallest of scales. Likewise, a realistic description fits the behaviour of objects in our everyday experience. But somewhere in the middle, something has to give, and the sharp lines thrown by these inequalities will be central to investigating boundary between the everyday and quantum worlds.

Are you overweight? The clue's in your poo

Baby it's warm inside ... we have 200 microbes for every human cell Agricultural Research Service

We are all populated by microbes – helpful or otherwise – which form a community known as a microbiome. Recent research by Ryan Newton and co-workers has shown that sewage-based analysis of the human microbiome can be used to diagnose health issues at a population level.

Large-scale monitoring of human populations and their activities takes many forms, from satellite imagery to censuses, providing data that can inform future policies. At this scale, we can collect and store data to assess the health of a nation. Projects such as BiobankUK and the 100,000 genomes project aim to fully describe human genetics and health at the cellular and molecular level, whilst revealing information at an individual and population level. This will result in the creation of a UK disease map, possibly linked to genetic information and factors that significantly affect health.

These projects focus on the human genome – yet we are not just human. Each of us is populated by microbes: bacteria, viruses, fungi and protozoa. Bacterial cells alone outnumber our own by a factor of 20. No one has estimated the number of viruses, but we expect between ten and a hundred times more than the bacteria. In the body, microbial genes outnumber human genes by a factor of 200.

We are now able to look not only at the numbers of microbes in the body, but can also find out what they are and determine their functions. DNA sequencing on very large scales indicates which bacteria dominate different environments and different processes. This sequencing defines the identity of the microbes. When targeted correctly, it can also define function at a molecular level. This is particularly useful in describing the human microbiome and its value to human health.

The microbes that form our microbiome provide protection against disease, top up our immune system, help metabolise our food into simpler more useful compounds and provide some essential nutrients such as vitamin K. The genetic profile of bacteria in faeces provides individual microbial fingerprints. This shows that the microbiome in all humans has a shared essential microbial function whilst having some variability in its microbial composition.

Whodunnit? Microbes in our gut have a distinctive ‘fingerprint’ that reveals their identity

Gut microbes also vary with progressing age, dietary changes, disease states and across differing human populations. Changes in the diversity of the microbiome are associated with certain chronic illnesses such as inflammatory bowel disease. By looking at the microbial profiles of bacteria in the colon we can even show a difference between people with Crohn’s disease and irritable bowel syndrome compared to people with ulcerative colitis.

This type of diagonistic analysis has now been taken a step further. Whilst recognising that faeces are a proxy for the gut microbiome within and among human population, Ryan Newton and co-workers examined sewage samples and compared them to human faecal samples. They showed that sewage effluent accurately reflects a composite faecal microbiome from human populations not only at an individual level but over different demographic scales – city, country, or continent – using 71 cities in the USA as a sampling ground.

Sorting the fat from the lean

Among the core set of organisms detected, significant variation was seen at a population level rather than at an individual level. This variation clustered into three primary community structures distinguished from different groups of microbes: Bacteroidaceae, Prevotellaceae, or Lachnospiraceae/Ruminococcaceae. These distribution patterns reflected human population variation and even predicted whether samples represented lean or obese populations with 81 to 89% accuracy.

So why not just observe the “fat and lean” by sitting at a busy railway station in disguise rather than extract the bacteria from sewage? Well, not everyone in the population will pass the detective’s observation point but almost all will submit their sample to the sewer, to be subjected to sewage molecular “satellite” imagery. And sewage can be used to analyse many more health issues than simply the weight of the population.

Of course there will be limitations to this approach. But as a means for analysing data at a city, country or continental level, the limiting factor may simply be how many samples we can collect and analyse.

The full potential of this technique has yet to be realised but advances in sequencing and bioformatics – coupled with increasing sensitivities of analysis – could make sewage monitoring a routine part of health analysis. This could be used to inform policy at local and national scales and ultimately could even benefit personal health strategies.

Dawn of a new era: the revolutionary ion engine that took spacecraft to Ceres

I've seen the future, and the future's blue. NASA

The NASA spacecraft Dawn has spent more than seven years travelling across the Solar System to intercept the asteroid Vesta and the dwarf planet Ceres. Now in orbit around Ceres, the probe has returned the first images and data from these distant objects. But inside Dawn itself is another first – the spacecraft is the first exploratory space mission to use an electrically-powered ion engine rather than conventional rockets.

The mysterious bright spot of Ceres seen as Dawn approaches. NASA

The ion engine will propel the next generation of spacecraft. Electric power is used to create charged particles of the fuel, usually the gas xenon, and accelerate them to extremely high velocities. The exhaust velocity of conventional rockets is limited by the chemical energy stored in the fuel’s molecular bonds, which limits the thrust to about 5km/s. Ion engines are in principle limited only by the electrical power available on the spacecraft, but typically the exhaust speed of the charged particles range from 15km/s to 35km/s.

What this means in practice is that electrically powered thrusters are much more fuel efficient than chemical ones, so an enormous amount of mass can be saved through the need for less fuel onboard. With the cost to launch a single kilogramme of mass into Earth orbit of around US$20,000, this can make spacecraft significantly cheaper.

This can be of great benefit to commercial manufacturers of geostationary satellites, where electric propulsion can allow them to manoeuvre adding new capabilities to the satellite during its mission. However, for scientific missions such as interplanetary travel to the outer regions of the Solar System, electric propulsion is the only means to carry useful scientific payload quickly across the enormous distances involved.

Inside an ion engine. NASA

Electric space power

There are three broad types of electric propulsion, depending on the method used to accelerate the fuel.

Electrothermal engines use electric power to heat the propellant either by passing a current through a heating element, a configuration known as a resistojets, or by passing a current through the hot ionized gas or plasma itself, an arcjet.

Electromagnetic engines ionise the propellant by turning it into an electrically conductive plasma, which is accelerated via the interaction of a high electrical current and a magnetic field. Known as pulsed plasma thrusters, this technique is in fact quite similar to how an electric motor works.

Electrostatic engines use an electric field generated by applying a high voltage to two grids perforated with many tiny holes to accelerate the propellant, called a gridded ion engine, which is what powers Dawn. Another electrostatic design is the Hall effect thruster, which operates in a similar fashion but instead of high voltage grids generates an electric field at the thruster’s exit plane by trapping electrons in a magnetic field.

Half a century in the making

The concept of electric propulsion has been around for 50 years or more, but was deemed too experimental to commit to major projects. Only now is it beginning to find real applications. For example, keeping geostationary satellites in their correct orbit, to counteract the aerodynamic drag from the very tenuous atmosphere 200km above the Earth. Or interplanetary missions such as Deep Space 1 – the first experimental mission to use ion engines, it was originally intended as a technology demonstrator but performed a successful fly-past of the asteroid 9969 Braille and the comet Borrelly 15 years ago.

Another very successful mission using ion engines was the ESA Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite which for four years until 2013 was able to map in unprecedented detail the Earth’s gravity field.

The Dawn spacecraft, equipped with large solar panels to power its electrical engine. NASA

Future designs

Now that electric spacecraft engines have entered mainstream use, they look set to reduce the cost of deploying satellites. With compact ion engines onboard, satellites can raise themselves from low Earth orbit to their final geostationary orbit under their own power. This will save enormous amounts of fuel required to lift the satellite through conventional chemical rockets, and allow the use of much smaller launch vehicles which will save a lot of money. Boeing was the first off the blocks in 2012 with an all-electric version of their 702 platform satellite fitted with xenon-powered gridded ion engines, and other satellite manufacturers are following suit.

Currently all electric power designs use xenon gas as the propellant, but the search is on for alternative propellants since xenon is enormously expensive and in limited supply. But electrical power is here to stay, and over the longer term, space tugs and even manned missions to Mars based on nuclear electric propulsion will be the next on the drawing board.

New nanomaterials will boost renewable energy

Fossil fuels can only go so far towards meeting our burgeoning energy demands Shutterstock

Global energy consumption is accelerating at an alarming rate. There are three main causes: rapid economic expansion, population growth, and increased reliance on energy-based appliances across the world.

Our rising energy demand and the environmental impact of traditional fuels pose serious challenges to human health, energy security, and environmental protection. It has been estimated that the world will need to double its energy supply by 2050 and it is critical that we develop new types of energy to meet this challenge.

Fuel cells usually use expensive platinum electrodes, but a non-metal alternative could be an affordable solution for energy security. Fuel cells generate electricity by oxidizing fuel into water, providing clean and sustainable power.

Hydrogen can be used as the fuel. First, hydrogen is split into its constituent electrons and protons. Then the flow of electrons generates electrical power, before the electrons and protons join with reduced oxygen, forming water as the only by-product.

This technology has high energy conversion efficiency, creates virtually no pollution, and has the potential for large-scale use. However, the vital reaction which generates reduced oxygen in fuel cells requires a catalyst – traditionally a platinum electrode. Unfortunately, the high cost and limited resources have made this precious metal catalyst the primary barrier to mass-market fuel cells.

The high cost of platinum can make electrodes – as well as engagements – prohibitively expensive. 1791 Diamonds, CC BY

Ever since fuel cells using platinum were developed for the Apollo lunar mission in the 1960s, researchers have been developing catalysts made from alloys containing platinum alongside cheaper metals. These alloy catalysts have a lower platinum content, yet commercial mass production still requires large amounts of platinum. To make fuel cells a viable large-scale energy option, we need other efficient, low cost, and stable electrodes.

We previously discovered a new class of low-cost metal-free catalysts based on carbon nanotubes with added nitrogen, which performed better than platinum in basic fuel cells. The improved catalytic performance can be attributed to the electron-accepting ability of the nitrogen atoms, which aids the oxygen reduction reaction. These carbon-based, metal-free catalysts could dramatically reduce the cost of commercialising of fuel cell technology. Unfortunately, they are often found to be less effective in acidic conditions – the typical conditions in mainstream fuel cells.

Using carbon composites with a porous structure to increase surface area and nanotubes to enhance conductivity, our latest research demonstrates that our nanomaterials are able to catalyse oxygen reduction as efficiently as the state-of-the-art non-precious metal catalysts – and with a longer stability. This first successful attempt at using carbon-based metal-free catalysts in acidic fuel cells could facilitate the commercialisation of affordable and durable fuel cells.

In addition to fuel cells, these new metal-free carbon nanomaterial catalysts are also efficient electrodes for low-cost solar cells, supercapacitors for energy storage, and water splitting systems which generate fuel from water. The widespread use of carbon-based metal-free catalysts will therefore result in better fuel economy, a decrease in harmful emissions, and a reduced reliance on petroleum sources. This could dramatically affect life in the near future.

Warning: the truth behind handshake-sniffing may bum you out

"Lovely day for it." "Woof yes!" Craig Roberts

As we all know, a firm handshake is important in making a good first impression. It’s a sure sign of physical strength and, rightly or wrongly, we use it make all manner of judgements about character, personality and sincerity.

New research now suggests that we take away much more than this – quite literally – because shaking hands may also be a way that we smell each other. As you may have read elsewhere, an Israeli team published a paper that showed that handshakes transfer aromatic compounds thought to be involved in social assessment – that is, making judgements about someone else by virtue of how they smell.

‘Don’t forget to sniff!’ Isa Sorensen, CC BY-SA

They analysed the chemical compounds present on clean surgical gloves and those that had been worn during a single handshake with the bare hands of ten volunteers. A range of chemical compounds were transferred, including some involved in animal interactions or already known to occur in human skin secretions.

So handshakes transfer smelly compounds. And how often we smell our hands following a handshake depends on who we greet. By secretly filming 150 participants, the researchers found that both men and women spent more time smelling the hand they used in the handshake when they greeted someone of the same gender. When they greeted a member of the opposite sex, they spent more time smelling their non-shaking hand.

Smell and social interaction

These new results add to accumulating evidence that our sense of smell plays an important part in social interactions. We can detect whether someone is sick or healthy through their body odour, or whether they are fearful, for example. Women place particular value on smell when judging suitability of potential partners, and prefer armpit odour of men who, among other qualities, are more genetically compatible or socially dominant.

In turn, men find women’s armpit odour more attractive when women are close to ovulation and exposure to vulvar scents collected around ovulation increases their testosterone levels, suggesting that scent might prime men for competition over a fertile woman. Interestingly, women respond to fertile odour in just the same way, suggesting they are also sensitive to smells of potential competitors.

So what exactly might we be assessing when we check out hand odour, and what might we use that information for?

Smell is usually thought to be important in sex and attraction, so it was surprising that sniffing of the shaking hand increased the most after greeting someone of the same sex. The researchers suggested that this could be a way to assess the competition (though they admit they did not ask about sexual orientation of the participants).

That would not completely rule out using hands to sniff out potential partners. Reactions to smells can change depending on context, so perhaps people increase focus on the opposite sex in more socially relevant settings, or if they are single and searching for someone special.

But it’s not about the hands

One problem with all this is that it remains unclear whether there is some particular communicatory value in the smell of a hand. So far as we know, there are no special secretory glands that are unique to the hand – the compounds present on hands are likely to be much the same as those that occur on many other parts of the body.

Bad plan? okili77

Yet we do use our hands to touch other parts of our body which produce specific and localised odours, including our lips, hair and, of course, more intimate areas. The researchers did not provide evidence that these are the source of some of the transferred smell compounds, but it seems plausible. Indeed, studies aiming to promote handwashing report all kinds of bodily traces, including faecal bacteria, on hands of ordinary people on the street.

This could provide the key to understanding hand-smelling. A simple handshake is a world away from the greeting ceremonies of other mammals. They are unconstrained by the social niceties of observing personal space and partake in abundant close-up sniffing, very often in the ano-genital area.

We simply don’t get to do this until we enter an intimate sexual relationship. But because hands wander, they pick up these more intimate odours and make them accessible in a socially acceptable way. In other words, offering a handshake could just be a polite and modern version of inviting someone to “sniff my butt”.