Solar eclipses offer opportunity for science, as well as for awe and wonder

A lucky gap in the clouds. Kevin Pimbblet, Author provided

A solar eclipse is a rare event to witness first hand. A wag might add that once you’ve factored in the British weather they’re rarer still, however observers in some areas of the UK managed to peer through the clouds and experience a partial solar eclipse from Exeter and Truro in the South-West to Nottingham in the Midlands, and Hull and Newcastle and the North-East.

The reason solar eclipses are rare is due to the orbit of the moon around the Earth, which is inclined by about five degrees to Earth’s orbit around the sun. This means that not only must the moon be a new moon in order to put it in the sky during daylight hours, but it must also be in just the correct arc of its orbit that it is aligned directly between the Earth and the sun.

A lunar eclipse, where the Earth comes between the sun and the moon, darkening the moon by blocking the sun’s light, can be seen by most people on the dark side of the Earth. But not everyone on the daylight side of the Earth will see a solar eclipse, because the shadow of the moon on the Earth’s surface covers only a band across the planet. To witness complete totality during an eclipse observers must be in an even more narrow band just 250km (150 miles) wide. This is why the best views were restricted to the islands of Svalbard and the Faroes this year.

Scientific opportunities in the dark

Scientifically speaking, eclipses have had a rich history in helping scientists conduct certain types of experiment and making unique discoveries.

A total solar eclipse was used to test gravity as described by Newtonian physics against predictions made by Einstein’s new theory of General Relativity. Both forms of gravitation predict that light can be bent around the sun, but by different amounts. In order to see other celestial objects – such as background stars – near the disk of the sun, the only thing to do was await a total solar eclipse. This happened in 1919, when Arthur Eddington and others simultaneously made measurements of the positions of stars close to the sun during an eclipse. They found that light was bent by the extent predicted by general relativity, rather than classical Newtonian physics. This proved to be the first of many spectacular successes for general relativity.

The sun is not the only celestial body to be eclipsed – or occulted – by the moon. In 1962, a lunar occultation technique was employed at the Parkes Telescope to determine that a quasar (a bright point-like object that appeared like a star) consisted of two elements. This use of occultations yielded the positions and further details of these elements which led to an astronomical revolution. Quasars are exceptionally powerful extra-galactic objects.

Eclipse concepts in use elsewhere

Today we can use the idea of occultations even to predict the weather. This uses Global Positioning Satellites (GPS) that constantly transmit their positions to listening stations worldwide. All that is required is for part of the atmosphere to occult and block the signal between one satellite and another. This results in refraction, where the radio signal is bent through the atmosphere. Critically, the amount of refraction is highly dependant upon the conditions in the atmosphere, for example water vapour density and ambient temperature. So based on these factors we can produce an instantaneous mapping of the current weather, and additional data to predict the future weather, based on the degree of refraction encountered.

Further away from home, we can use the idea of occultations to help derive the size of other planets orbiting distant stars. When a planet passes in front of a distant star in the line of sight to Earth, it creates an apparent partial eclipse that causes a dip in the observed light from that star. We can deduce the size of the planet by measuring how much light is blocked out during its transit.

So while solar eclipses are not a common sight, they’re certainly an opportunity for scientists to learn more about the world and the laws that govern the Universe – naturally occurring phenomena that we’re lucky to have the opportunity to observe from time to time.

Five things Discworld will teach you about science

Terry making Jack and I honorary wizards of Unseen University. Warwick University

One evening, in a Mongolian restaurant, Terry Pratchett, Jack Cohen and I came up with the idea of a popular science book based on Discworld. We all felt that this would be an attractive way to explain science to non-specialists, and that this was a worthwhile thing to do. Unfortunately, as Terry pointed out in his usual direct manner, Discworld runs on magic. It has no direct relation to science.

Eventually the three of us got round this obstacle: the wizards of Unseen University accidentally create a containment field that keeps magic out. Inside is Roundworld, our planet/universe, and it runs on science. From the point of view of Discworld, things we take for granted start to look very strange. The result of this comparing and contrasting was The Science of Discworld, which became a series of four books that we wrote with Terry.

So here are five examples of what Discworld can teach us about science.

Round worlds

Discworld is flat, carried by four elephants standing on a turtle. This is the sensible way to make a world: it’s shaped the way it appears to be, something stops it falling, and it is self-propelled. Roundworld is a silly shape for living on, things ought to fall off, and it swims through space unsupported, which is surprising for a large rock.

The science that explains why round – but a bit flattened – is a sensible shape for a world includes gravity, momentum, and the behaviour of rotating liquids. There’s also the psychology of why we think our senses convey a complete view of reality, rather than a limited and transformed one.

Much more sensible. mdpettitt/flickr, CC BY

Chaos butterfly

In the 17th Discworld novel, Interesting Times, Terry investigates the workings of chaos, including aspects of “chaos theory”, the mathematical discovery that deterministic laws can have apparently random effects. He gives the famous quantum weather butterfly a cameo role as Papilio tempestae. It flaps its wings … and freak gales cause road chaos.

This alludes to the famous “butterfly effect” in chaos theory link, where the flap of a butterfly’s wing can change the weather to something totally different. His suggested solution is “finding that bloody butterfly … and getting it to stop”.

Weather forecasters find it more effective to simulate the weather many times with slightly different random perturbations, in effect trying to find out which butterfly wins. Of course butterflies don’t cause hurricanes – but they affect where and when they occur, all else being equal.

Cat in a box

The witch Nanny Ogg’s cat Greebo is a recurring character of the books. He is tough and streetwise, though Nanny considers him a big softie. When Greebo gets shut in a box in Lords and Ladies, Terry tells us there are three states for a cat in a box: alive, dead, and absolutely bloody furious.

This is an allusion to Schrödinger’s cat, the famous thought experiment in which a cat in a box that you cannot see into is simultaneously both alive and dead because of quantum mechanics … that is, until you open the box and find out which.

Terry’s joke puts quantum observations in a new light. For starters, “alive” and “dead” are not the only alternatives, even in classical physics.

God of evolution

Discworld has a god for almost everything, from Flatulus, god of the winds, to Bilious, the “Oh God of Hangovers”. In particular it has a god of evolution, which puts the science/religion debate in a typically Pratchettian light.

In The Science of Discworld III: Darwin’s Watch the Reverend Charles Darwin writes Theology of Species instead of The Origin of Species. The result? Roundworld stagnates.

While getting it back on track in time to avoid an inbound comet, the wizards introduce Darwin to the god of evolution. Darwin particularly admires the wheels on his elephant. This encounter opens up the entire topic of evolution and why creationist objections are nonsense.

Ate by eight

On Discworld, the number eight is special: the number of magic. There is an eighth magical colour, octarine. The eight son of an eighth son has to become a wizard – even when the midwife gets the sex wrong. No one dares mention the number by name because of the evil god Bel-Shamharoth: you might get ate, OK?

In Roundworld, the number eight is also key, but for a different reason: it plays a key role in atomic structure. Electrons surround the nucleus in concentric shells (energy levels). In principle successive shells can contain up to 2, 8, 18, 32, 50, and 72 electrons, but in practice they tend to fill up when they have eight electrons. The number of electrons in the outer shell determines the atom’s chemical properties. Noble gases have eight outer electrons (only two for Helium since it fills only the first shell) and seldom combine with other elements. So it is a magic number, in a way.

It has been a privilege and an honour to be part of Terry’s Discworld universe, and it is typical of his generosity that he allowed us to do so. And so we mourn his passing, while celebrating his achievements.

Explainer: what are fundamental particles?

The epoch of the leptons existed for nine seconds after the Big Bang. Big Bang by Shutterstock

It is often claimed that the Ancient Greeks were the first to identify objects that have no size, yet are able to build up the world around us through their interactions. And as we are able to observe the world in tinier and tinier detail through microscopes of increasing power, it is natural to wonder what these objects are made of.

We believe we have found some of these objects: subatomic particles, or fundamental particles, which having no size can have no substructure. We are now seeking to explain the properties of these particles and working to show how these can be used to explain the contents of the universe.

There are two types of fundamental particles: matter particles, some of which combine to produce the world about us, and force particles – one of which, the photon, is responsible for electromagnetic radiation. These are classified in the standard model of particle physics, which theorises how the basic building blocks of matter interact, governed by fundamental forces. Matter particles are fermions while force particles are bosons.

Matter particles: quarks and leptons

Matter particles are split into two groups: quarks and leptons – there are six of these, each with a corresponding partner.

Leptons are divided into three pairs. Each pair has an elementary particle with a charge and one with no charge – one that is much lighter and extremely difficult to detect. The lightest of these pairs is the electron and electron-neutrino.

And then some. James Childs, CC BY

The charged electron is responsible for electric currents. Its uncharged partner, known as the electron-neutrino, is produced copiously in the sun and these interact so weakly with their surroundings that they pass unhindered through the Earth. A million of them pass through every square centimetre of your body every second, day and night.

Electron-neutrinos are produced in unimaginable numbers during supernova explosions and it is these particles that disperse elements produced by nuclear burning into the universe. These elements include the carbon from which we are made, the oxygen we breathe, and almost everything else on earth. Therefore, in spite of the reluctance of neutrinos to interact with other fundamental particles, they are vital for our existence. The other two neutrino pairs (called muon and muon neutrino, tau and tau neutrino) appear to be just heavier versions of the electron.

J J Thomson’s 1897 cathode ray tube with magnet coils – used to discover the electron. Science Museum London, CC BY-SA

Since normal matter does not contain these particles it may seem that they are an unnecessary complication. However during the first one to ten seconds of the universe following the Big Bang, they had a crucial role to play in establishing the structure of the universe in which we live – known as the Lepton Epoch.

The six quarks are also split into three pairs with whimsical names: “up” with “down”, “charm” with “strange”, and “top” with “bottom” (previously called “truth” and “beauty” though regrettably changed). The up and down quarks stick together to form the protons and neutrons which lie at the heart of every atom. Again only the lightest pair of quarks are found in normal matter, the charm/strange and top/bottom pairs seem to play no role in the universe as it now exists, but, like the heavier leptons, played a role in the early moments of the universe and helped to create one that is amenable to our existence.

Force particles

There are six force particles in the standard model, which create the interactions between matter particles. They are divided into four fundamental forces: gravitational, electromagnetic, strong and weak forces.

A photon is a particle of light and is responsible for electric and magnetic fields, created by the exchange of photons from one charged object to another.

The gluon produces the force responsible for holding quarks together to form protons and neutrons, and for holding those protons and neutrons together to form heavier nuclei.

Three particles named the “W plus”, the “W minus” and the “Z zero” – referred to as intermediate vector bosons – are responsible for the process of radioactive decay and for the processes in the sun which cause it to shine. A sixth force particle, the graviton, is believed to be responsible for gravitation, but has not yet been observed.

Anti-matter: the science fiction reality

We also know of the existence of anti-matter. This is a concept much beloved by science fiction writers, but it really does exist. Anti-matter particles have been frequently observed. For example, the positron (the anti-particle of the electron) is used in medicine to map our internal organs using positron emission tomography (PET). Famously when a particle meets its anti-particle they both annihilate each other and a burst of energy is produced. A PET scanner is used to detect this.

Each of the matter particles above has a partner particle which has the same mass, but opposite electric charge, so we can double the number of matter particles (six quarks and six leptons) to arrive at a final number of 24.

We give matter quarks a number of +1 and anti-matter quarks a value of -1. If we add up the number of matter quarks plus the number of anti-matter quarks then we get the net number of quarks in the universe, this never varies. If we have enough energy we can create any of the matter quarks as long as we create an anti-matter quark at the same time. In the early moments of the universe these particles were being created continuously – now they are only created in the collisions of cosmic rays with the atmosphere of planets and stars.

The famous Higgs boson

There is a final particle which completes the roll call of particles in what is referred as the standard model of particle physics so far described. It is the Higgs, predicted by Peter Higgs 50 years ago, and whose discovery at CERN in 2012 led to a Nobel Prize for Higgs and Francois Englert.

The Higgs boson is an odd particle: it is the second heaviest of the standard model particles and it resists a simple explanation. It is often said to be the origin of mass, which is true, but misleading. It gives mass to the quarks, and quarks make up the protons and neutrons, but only 2% of the mass of protons and neutrons is provided by the quarks, and the rest is from the energy in the gluons.

At this point we have accounted for all the particles required by the standard model: six force particles, 24 matter particles and one Higgs particle – a total of 31 fundamental particles. Despite what we know about them, their properties have not been measured well enough to allow us to say definitively that these particles are all that is needed to build the universe we see around us, and we certainly don’t have all the answers. The next run of the Large Hadron Collider will allow us to refine our measurements of some of these properties – but there is something else.

The great collider. Image Editor, CC BY

Yet the theory is still wrong

The beautiful theory, the standard model, has been tested and re-tested over two decades and more; and we have not yet made a measurement that is in contradiction with our predictions. But we know that the standard model must be wrong. When we collide two fundamental particles together a number of outcomes are possible. Our theory allows us to calculate the probability that any particular outcome can occur, but at energies beyond which we have so far achieved it predicts that some of these outcomes occur with a probability of greater than 100% – clearly nonsense.

Theoretical physicists have spent much effort in trying to construct a theory which gives sensible answers at all energies, while giving the same answer as the standard model in every circumstance in which the standard model has been tested.

The most common modification implies that there are very heavy undiscovered particles. The fact they are heavy means lots of energy will be needed to produce them. The properties of these extra particles can be chosen to make sure that the resulting theory gives sensible answers at all energies, but they have no effect on the measurements that agree so well with the standard model.

The number of these undiscovered and as-yet-unseen particles depends on which theory you choose to believe. The most popular class of these theories are called supersymmetric theories and they imply that all the particles which we have seen have a much heavier counterpart. However, if they are too heavy, problems will arise at energies we can produce before these particles are found. But the energies that will be reached in the next run of the LHC are high enough that an absence of new particles will be a blow to all supersymmetric theories.

Solar eclipse: a rare opportunity to bask in the moon's shadow

As visible from Europe (weather permitting). Luc Viatour, CC BY

A total solar eclipse is an extraordinary visual and emotional experience, from the moon’s first bite out of the sun’s unblemished disc, to the moment that the daylight sky becomes dark and the sun’s blazing light is muted. The temperature drops, the moon’s shadow can be seen speeding across the Earth’s surface, and there is a sudden silence as animals settle down to sleep under the impression that night has fallen.

Yet the fact that we see a solar eclipse at all is something of a miracle. Ours is the only planet in the solar system whose moon appears from the surface to have the same angular size in the sky as that of the sun: it is 400 times smaller, but also 400 times closer. This cosmological coincidence allows the moon to completely block out the sun to reveal the ethereal beauty of its tenuous outer atmosphere, the corona, to those fortunate enough to be standing in the shadow of the moon.

John Couch Adams, who discovered Neptune, wrote in 1851:

The appearance of the corona, shining with a cold unearthly light, made an impression on my mind which can never be effaced, and an involuntary feeling of loneliness and disquietude came upon me.

I consider myself extremely fortunate to have witnessed four total solar eclipses so far. This, my fifth, will be the first solar eclipse visible in Europe since 1999, and the last until 2026. A total solar eclipse happens somewhere on the planet on average every 18 months, but for the moon’s shadow to pass over inhibited land is far less common.

Central eclipses. Fred Espenak/NASA, CC BY

A rare solar eclipse in Europe

The solar eclipse will begin in the mid-Atlantic at sunrise, travelling north-east between Iceland and the UK and Ireland, before ending at the North Pole. The only islands from which totality – the moment when the moon entirely eclipses the sun leaving only a fiery halo – will be visible is remote Svalbard in the Arctic and the Danish-owned Faroe Islands, where I intend to be.

In the UK and Ireland, depending on your location, the maximum coverage will be a partial eclipse of between 85-97% of the sun’s disk, with the degree increasing towards the north. However, even almost entirely occluded in this way, the sun is still bright enough to cause severe eye damage and so precautions must be taken. A partial eclipse is best viewed through special eclipse glasses (not sunglasses), or by projecting the sun’s image onto a piece of white card using a pinhole projector – do not look directly at the sun.

The Faroe Islands, North Atlantic - one of the few places to witness the total eclipse. Erik Christensen, CC BY-SA

Scientific riches

Aside from being the most awe-inspiring sight in nature, solar eclipses also have immense scientific value. The element helium was discovered as a result of solar eclipse observations, decades before it was detected on Earth. Einstein’s theory of general relativity was proven correct thanks to a solar eclipse, when a star’s apparent position in the sky was “shifted” due to the gravitational influence of the sun. And the technique of spectroscopy led to the discovery that the sun’s corona holds a temperature of over 1,000,000°C – a thousand times hotter than its surface. This has become known as the coronal heating problem, something scientists are still grappling with today. Even now in the 21st century, with advanced scientific instruments both on the ground and in orbit, we cannot reproduce the conditions that nature provides during totality.

A colossal coronal ejection in 2012 gives some indication of the forces involved. NASA, CC BY

The technology we have come to depend upon is at the mercy of catastrophic explosions that originate in the sun’s atmosphere. Solar flares and coronal mass ejections are a consequence of the sun’s contorted coronal magnetic field which, when stretched beyond breaking point, spews plumes of radiation and charged particles in the direction of Earth, putting our electronic infrastructure at risk. Studying the inner corona during a solar eclipse allows us to quantify the state of the sun’s magnetic field, which will help us understand how solar storms get accelerated and the origins of the solar wind, among other things.

It’s a bit late to start planning a North Atlantic trip now, but bear in mind that in August 2017 the moon’s shadow will traverse the entire continental US, from Oregon to the Carolinas, making it one of the most accessible total eclipses of a generation. If you possess any sense of wonder and adventure, then you owe it to yourself to find a way of experiencing this fascinating phenomenon first hand. Then you can join in the chorus heard after the moon’s shadow has passed: “When is the next one?”

The dusky dottyback, a master of disguise in the animal world

Same fish, different colour. N Justin Marshall, Author provided

The cautionary tale of the wolf in sheep’s clothing warns that a familiar exterior can hide malicious intent. Like humans, other animals also deceive one another in this way, and our new study in Current Biology reveals that the dusky dottyback fish, Pseudochromis fuscus, is a true master of disguise.

A dottyback (rear) eying up a damselfish (front) Christopher E Mirbach

The dottyback is a small coral reef fish that lives on reefs from Madagascar to Australia. On the reefs off Lizard Island on the Great Barrier Reef, adults are either yellow or brown. Yellow dottybacks are often found on live coral among yellow damselfish, while brown dottybacks are often found on coral rubble amongst brown damselfish. Both brown and yellow dottybacks primarily prey upon damselfish juveniles.

Previous work had found that yellow and brown dottybacks are different morphs of the same species, but why the different morphs had evolved wasn’t known. It might be for camouflage from predators against the differently coloured habitats. Or, like a wolf in sheep’s clothing, perhaps the colour of the different morphs is to match the similarly coloured adult damselfishes, allowing them to sneak up on their young. There were reports of yellow dottybacks turning brown when placed on coral rubble, suggesting that something interesting was going on.

Video abstract for Current Biology (video by Alex Vail)

Hunter or hunted?

To disentangle the possibilities of why the dottyback morphs were coloured differently, we created artificial reefs made of either coral rubble (brown) or live coral (yellow), stocked them with either yellow or brown damselfish and introduced either a yellow or brown dottyback.

After two weeks we found that the yellow dottybacks on reefs with brown damselfish turned brown, and vice-versa. This colour change happened regardless of the dottybacks' habitat, so it was the colour of the damselfish driving the change.

A brown dottyback in its natural habitat Christopher E Mirbach

In most fish, colour change derives from an increase or decrease in abundance of one pigment type. By analysing skin samples in dottybacks we found they changed colour by altering the relative abundance of two different pigment types – something not previously reported in other fish species.

So it seemed as though dottybacks were changing colour to resemble adult damselfish in order to more easily prey upon their young. To test this, we carried out some aquarium experiments.

Black/brown (melanophores) and yellow (xanthophores) pigment cells in dottyback skin Fabio Cortesi

To catch a wolf

First, we stocked tanks with yellow or brown adult damselfishes, juvenile damselfishes, and a yellow or brown dottyback and left them for 24 hours. Checking how many juveniles had been eaten by the dottyback, we found that adult dottybacks the same colour as adult damselfish were much more successful at catching young damselfish snacks compared to those dottybacks with mismatched colouration.

Next, we placed a dottyback in a tank with one brown and one yellow juvenile damselfish. Again, dottybacks would more often catch juveniles that were the same colour as themselves. This suggests that juvenile damselfish lower their defences when dottybacks resemble their adults of their own species.

A yellow dottyback in its natural habitat Christopher E Mirbach

At this point we could see the dottybacks colour change was to mimic the colour of damselfish adults and lure in their young to be eaten. Could there be other benefits, however, such as protection from predators?

To test this idea, we put pictures of yellow or brown dottybacks in front of live coral or coral rubble backgrounds. We calibrated these pictures for the visual system of the coral trout, Plectropomus leopardus, which preys upon adult dottybacks and damselfishes. Using these and control images, we tested whether the dottyback’s colouration helped them avoid ending up as another fish’s lunch, as well as helping them find their own. Sure enough, dottyback colour morphs in their usual habitat (for example, yellow dottyback on yellow coral) were less vulnerable to the trout’s attacks than if their colour was mismatched to the colour of their habitat.

This sort of mimicry has been suggested in other species, such as the mimic octopus (Thaumoctopus mimicus) but this is the first time it’s been quantitatively proven. At least for the time being, this study shows that the dottyback is the reigning master of disguise in the animal kingdom.

Internet Explorer: reports of its death are greatly exaggerated

The end of IE? Wake up and smell the coffee. yukop, CC BY-SA

There are claims that Microsoft is to retire its web browser Internet Explorer and replace it with an all-new browser called Spartan with the upcoming release of Windows 10.

As of February 2015, Internet Explorer (IE) browser market share slipped to second place with around 17%, while Google’s Chrome browser boasts over 42%. One clear challenge for Microsoft is that it has always been committed to producing its own browser for its own Windows operating system (supporting IE on Apple Macs for a brief period). Apple on the other hand is happy to produce versions of its Safari browser for both Mac OS X and Windows, and Google produces versions of Chrome for every popular desktop and mobile operating system.

Perhaps Microsoft feels it’s time to take some action – in which case what is it trying to accomplish?

A quick history

Internet Explorer (IE) was introduced as an add on for Windows 95 and was a key part of the internet boom of the 1990s. Bundled free in all subsequent versions of Windows, IE soon gained dominance, winning the browser war against its older competitor, Netscape.

With a browser share that grew to be as substantial as Microsoft Windows' dominance of the operating system market, Microsoft was subject to numerous anti-trust litigation cases in the US and Europe. Nevertheless some of the HTML elements introduced in IE, and the fact it was more forgiving of badly coded websites than Netscape, meant that IE had a lasting influence on web design and the way websites were designed. Especially for internal corporate websites, which often used Windows based systems.

I don’t always use IE, but when I do…

In the 2000s, disquiet over Microsoft’s anti-competitive behaviour and IE’s lack of proper standards support led to a flourishing of competitors, boosted by the open sourcing of Netscape, which would become the basis for the popular Firefox browser. In reaction to Microsoft’s approach of pushing its own technologies and ignoring open standards, the appeal of more rigorous web standards compliance demonstrated by other browsers including Opera, Safari and Chrome have since carved away at IE’s dominance. Additionally, IE became one of the worst offenders for security vulnerabilities. Since then, it’s become the browser everyone loves to hate.

Time for a realitIE check

Trident, Internet Explorer’s layout engine which turns HTML and code into readable web pages, is showing its age. Benchmarking sites show that it is the performance laggard of the competing products. It took until 2008 and Internet Explorer 8 before the browser passed the web standards compliance test, Acid2.

With 20 years of history, Microsoft’s hands are to some extent tied by the many organisations that have created web-based programs that rely on IE, or on particular implementations of features in certain versions of IE. Even versions changes can introduce problems; switching to a new browser and layout engine altogether is something else.

Whenever new applications, operating systems or technologies in general are introduced, there is always the demand for backwards compatibility due to the considerable investment in developing services to run on corporate systems, or on products built for others, dependent on IE-specific features. By failing to properly support and adhere to open standards throughout its long history, Microsoft has made a rod for its own back.

As stated in a Microsoft developer blog, the new Spartan browser will be based on the relatively standards-compliant Internet Explorer 11 engine, but purged of all the code required to support this 20-year legacy. The result is, one hopes, a modern layout engine that adheres to modern standards.

Spartan will, when required, load in the older Internet Explorer engine for backwards compatibility. So the question one might ask is, with so many older IE-compatible sites out there, how often will Spartan be using its new engine, and how often will it relapse to Internet Explorer’s Trident to perform its duty for legacy systems? This means two sets of code to maintain and keep secure. And with Trident living on inside Spartan, to what extent can IE truly be considered “dead”?

Microsoft have a long way to go to improve their web browser performance, but this is certainly a step in the right direction – even if, with a 20-year-legacy millstone around their neck, they may find themselves held back from further progress for some time to come.

Who do you think you are? Most detailed genetic map of the British Isles reveals all

Yorkshire: not in the top five distinct areas. Robert Lowe, CC BY

The history of Britain’s population is a familiar story to many. It tells of an ancient people (retrospectively dubbed the Celts) and subsequent invasion and settlement by the Romans, Anglo-Saxons, Normans and Vikings. And many people today still identify strongly with one or another of these groups.

However, historical records have their weaknesses. For example, it’s very difficult to know to what extent an invasion amounted to mass settlement replacing an existing population, and how much it was a small elite converting that existing population to a new way of life.

For some years, geneticists have been able to answer similar questions on a continental scale. Now, enough data has been collected to start to tackle some of these issues on a national level. The People of the British Isles (PoBI) project examined differences at more than 500,000 positions in the DNA of more than 2,000 people from the UK, thus creating the most detailed genetic map of any country in the world.

In a paper published in Nature, the authors describe how they looked for regional differences in genetic patterns and inferred ancestry from various past migrations.

European movements, as understood by historians. Many of these distinctions are now supported by genetic data. Nature

Splitting the population

First, they split the samples into the two most-different groups possible, without considering where each sample came from. This process was repeated, splitting off the next most distinct group and then the next, producing an increasingly subtle picture of diversity.

By then plotting these groups onto the map, it became clear that many of them were clustered in particular regions, suggesting a clear geographical pattern to genetic diversity in Britain. So, for example, the first split separated Orkney from the rest of the British Isles. This means that Orkney is more genetically distinct from the rest of the UK than any other regions are from each other.

It’s important to remember that these groups have much ancestry in common, and are in no way pure representations of historical peoples. In fact, those historical peoples themselves cannot be truly defined. However, similarities between modern populations in the UK and continental Europe can suggest where past migrations came from. To this end, DNA was collected from ten other European countries, and these too were divided based on their genetic diversity. These European groups were then compared to the British ones.

It wasn’t all Vikings

‘Viking’ times. mararie, CC BY

When compared to the various continental groups, 25% of DNA from Orkney appears to have come from the groups found in Norway.

This supports the long-held belief that Norse Vikings settled Orkney, but also shows that the majority of Orcadian ancestry predates this settlement.

However, Orkney was not the only area of the country to have been conquered by Vikings. The Danelaw was a large area of northern and eastern England, ruled over by Danish Vikings. Interestingly, the study found no genetic signature of this, suggesting that the Danelaw was overwhelmingly inhabited by pre-existing English people, and ruled over by a very small number of Danes.

Neolithic Skara Brae on Orkney. The DNA of these pre-Viking people still accounts for much of today’s Orcadian DNA. John Lord, CC BY

Scottish, English and Welsh

After Orkney, the second split separated Wales from the rest of the UK; the third, north from south Wales; the fourth, the far-north of England, Scotland, and Northern Ireland collectively from the rest of England; and the fifth, Cornwall from most of England. This shows that the “Celtic” groups are all genetically distinct from “Anglo-Saxon” England, but also from each other, and, for example, the Scottish and English are more similar to each other than either is to the Welsh.

Scottish and English more similar to each other than to the Welsh. khrawlings, CC BY

However the “Celtic” groups all had large contributions of ancestry from the same three continental groups (centred on France, Belgium and Germany), suggesting some common, but very ancient ancestry from Pre-Saxon peoples. Indeed, these three groups also contribute significant ancestry across the UK, suggesting that these pre-Saxon people were widespread, and nowhere were they completely replaced.

Another very notable feature is that, even after the population was split into 50 groups, almost half the samples remain in one large group, covering most of central, southern and eastern England. As this region has little in the way of geographical or political barriers, it appears that freedom of movement over the centuries has homogenised the genetics of its people. The people of this region have much ancestry from pre-Saxon groups, but also 10-40% from continental groups who barely contributed to the Welsh gene-pool at all. It seems altogether very likely that these were the Anglo-Saxons.

Outside the history books

The study also found evidence of migrations not found in history books. These include contributions from France, Spain and Scandinavia, after the peopling of Britain, but probably before the Saxon invasions, and even a later one from France into Wales which didn’t seem to go through England.

So by drawing such conclusions from high-resolution data, the PoBI project uncovers the movements of ordinary people, rather than the ruling classes emphasised by traditional approaches. They also provide a proof-of-principle for similar work around the world, and some applications for modern healthcare geneticists. Michael Dunn, Head of Genetics and Molecular Sciences at the Wellcome Trust, said:

These researchers have been able to use modern genetic techniques to provide answers to the centuries old question – where we come from. Beyond the fascinating insights into our history, this information could prove very useful from a health perspective, as building a picture of population genetics at this scale may in future help us to design better genetic studies to investigate disease.