Why is East Africa so Dry?

Peter deMenocal, a marine geologist at Columbia University, has been investigating about the natural history of eastern Africa for more than a decade. There is evidence of desiccation and gradual change to open savannahs, grass-eating fauna and the appearance of modern humans. Now he and his team have an explanation for that climate change: the tropical oceans.

They analysed planktonic foraminifera (small single-celled organisms) in an old sediment in the Indian Ocean off the west coast of Australia. These calcifying organisms take more and more magnesium when the water temperature goes up. About two million years ago, the level of magnesium grew up, indicating hot climate on the eastern side of the Indian Ocean. But on the other side of the ocean, off the coast of Africa, just the opposite happened: the ocean got colder.

This change in sea temperatures in the Indian Ocean came at an important time, coinciding with a rapid drying of east Africa, and the beginning of modern circulation in the Pacific Ocean. They tested the theory with a series of computer models and there it is: rain over east Africa depends on the conditions in the Indian Ocean and the Pacific Ocean.

Two to four million years ago is a significant time: it is then that the ice ages began, and a lot about humans is related to that period of the Earth. Can this climate change be connected to the evolutionary changes that happened at the same time, including the appearance of Homo Erectus and of animals adapted to the grasslands? Well, there is a lot of changes happening at the same time but it is difficult to prove that they are all related.

By Jeff Tollefson at www.nature.com. Picture by Top-Pics TBK / Alamy.

Lefthanders are Ambidextrous

If you're left-handed, there's good news. Well, most utensils and tools are still almost impossible to use. But at least your handedness is no longer humiliating. Lefties used to be strange creatures, as society considered them criminals. Left-handed children were forced to write with their right hand, although it was very difficult! Now times have changed. No longer shamed or mocked, the left-handed coexist with us peacefully. 

However, doctors continue to study handedness. For example, scientists don't know why the prevalence of lefties has remained consistently at 10% of humanity over time. Or exactly how being left-handed, which relates to brain symmetry, translates into other functions of the brain.

Left-handedness has been seen as a key to the complex anatomy of the brain, so investigators continue to look for links to many other conditions, including immune disorders, learning disabilities and dyslexia, reduced life expectancy and schizophrenia. But it's not so simple.

Brain lateralization, the distribution of function into right and left hemispheres, is crucial for understanding language, thought memory and perhaps even creativity. For many years, handedness has been seen as an external clue to the balance in the brain between left and right.

For right-handed people, language activity is predominantly on the left side. Many left-handers also have left-side language dominance, but a significant number have language predominantly on the right side of the brain.

In general, left-handers have less asymmetric brains, with more perfect distribution over the two hemispheres. Perhaps a more exact way to think about them is as non-right-handers, because many of them are ambidextrous.

By Megan Gibson at www.time.com and Perri Klass at www.nytimes.com. Picture by United Press International; Gary Cameron/Reuters; Jonathan Ernst/Reuters

A Close Look at Mercury

It took six years but on Thursday, March 17, NASA's Messenger spacecraft finally settled into orbit around the small planet Mercury. Now, for the first time, a spacecraft will observe Mercury for at least a year and may answer some questions.

Why, for example, is Mercury so much denser than Earth, Venus and Mars? Scientists know the basic reason: Mercury has less rock and a higher percentage of iron than the other planets, and iron is denser than rock. But how did Mercury end up that way?

Another question is whether there could be ice hiding in craters at Mercury's poles. Radar soundings taken from Earth show that there's something highly reflective inside, and because the crater floors are in perpetual shadow, it's cold enough for ice to exist. The spacecraft's neutron detectors will look for signs of hydrogen — the H in H2O — which would suggest it might be ice.

However, the most mysterious question is why Mercury has a magnetic field. In theory, you need molten iron in the core to generate one, but Mercury is so small, its core should have solidified.

And there's plenty more: Messenger carries no fewer than seven different instruments, including high-resolution cameras that will map just about every inch of the planet in extraordinary detail, picking out objects as small as 18 m across.

But anyone who follows astronomy knows that there's an important rule in space exploration: When you try a new, more powerful instrument on a celestial object you're sure to raise more questions than you answer. That is when the fun really begins.

By Michael Lemonick at www.time.com. Picture by NASA

Origin of Life

Stanley Miller and Harold Urey carried out experiments in the 1950s that were the first serious try to find out how life on earth began. They passed sparks through a combination of methane, ammonia, water vapor and hydrogen — a mixture similar to earth's original atmosphere. At the University of Chicago, they created amino acids, the building blocks of proteins. Their reconstructed atmosphere was probably wrong, and the experiment had never been repeated with a more exact mixture

But everyone was wrong. After Miller left Chicago, he worked with Jeffrey Bada, a chemist from the USA, at the Scripps Institution. When Miller died in 2007, Bada received boxes full of his paraphernalia. He did not worry about them much for some time, but one day...

"It was just a stunning experience," Bada says. "All these little boxes full of equipment and vials from all Stanley's original experiments. It was an unbelievable collection of organic compounds and amino acids."

The new studies are potentially important because they are based on a more realistic picture of conditions on early earth. In particular, they suggest that life might have appeared not in a "warm little pool" but in the violent environment of volcanic eruptions. "We know that the early earth had few continents, but it had a lot of volcanoes, and they were hotter and more powerful than today. They would have been throwing hydrogen sulfide and other gases."

Volcanic plumes would also have initiated powerful discharges of lightning from the skies. And that is essentially what Miller's unpublished experiments showed. And when the scientists analyzed Miller's original samples they found a wide assortment of amino acids, including some that had never been made before. 

The big action now is how go from these simple molecules to self-replicating molecules. It's challenging science. It's just a matter of time before we get to know it.

By Michael Lemonick at www.time.com. Picture by UPI Photo / Landov

Heart Surgery without Surgery

Cardiologists are talking about a major advance: A study suggests that many people with a bad aortic valve, the heart's most important gate, can avoid open-heart surgery and have a new one placed through a tube in an artery. There may be a problem — a higher risk of stroke — and nobody is sure about how long these valves will last.

The aortic valve can harden and narrow with age, making it difficult for the heart to push blood through it. Severe cases are treated with surgery to replace the valve, but that's risky for many older people who have this problem. Without an operation, half die within two years.

Through an artery in the chest a new heart valve is attached to a balloon and advanced across the narrowed, older, diseased heart valve. The balloon is inflated and the new valve left in place.

A test of this gentler treatment in people too sick for surgery improved survival, doctors reported last fall. The new study involved nearly 700 people eligible but at high risk for surgery. Their median age was 84, and they were randomly assigned to get valves replaced through surgery or the new way. Twenty-eight people refused treatment when they learned they had been placed in the surgery group.

In the end, both groups did very well. After one year, about 24 percent of the artery patients and 27 percent of the surgery patients had died — considerably fewer than doctors had predicted.

However, strokes were twice as common in the artery-treated group — 8 percent versus 4 percent.
AP / Marilyn Marchione at www.time.com. Picture by AP / Edwards Lifesciences.

Frogs and Teeth

Dollo’s Law, a theory proposed by the scientist Louis Dollo in the 1800s, says that when a particular property is lost in a species, it never comes back. It explains why humans have no tails, birds and turtles have no teeth and snakes have not regained legs.

But a new analysis about frogs, done by a scientist at Stony Brook University, found that they lost teeth in the lower jaw at least 200 million years ago, but a particular type of marsupial tree frog regained those lower teeth about 20 million years ago.

“It’s a very clear-cut case of re-evolution because of the large time span,” said John Wiens, the Stony Brook biologist who wrote the paper in the journal Evolution.

Dr. Wiens analyzed DNA samples of 170 modern and fossilized frogs to approximate the dates of loss and re-evolution of the teeth. Most frogs have teeth on their upper jaws, which may have made the re-evolution in the tree frog, known as Gastrotheca guentheri, easier, Dr. Wiens said. “They already had teeth in the upper jaw, so they had the enamel, dentine and other necessities,” he said. “There was a way to facilitate new teeth after 200 million years.”

The species is the only known modern frog species with lower teeth, though certain other species with upper teeth have structures similar to teeth on the lower jaw. “That’s a big question now: What’s preventing the other frogs from developing real teeth on the lower jaw?” Dr. Wiens said.

By Sindya N. Bhanoo at www.nytimes.com. Picture by Chris Gash.

Plants Have a Clock

Plants, like many other organisms, have circadian clocks that help them anticipate various environmental and biological events that occur at precise times of the day. Processes like photosynthesis, fragrance emission and time of bloom are all regulated by this timekeeping mechanism.

Now, scientists report in the journal Nature that genes in certain plants keep infections at a distance with the help of the clock as well. Twenty-two genes in the plant Arabidopsis, all connected to the plant’s ability to resist infection, were expressed only from the evening onward, reaching their highest point at the beginning of day.

The timing corresponds with the formation of spores in a funguslike pathogen that attacks the plant and results in a condition known as mildew disease. The disease weakens the plant and forms a repugnant layer of mildew.

“From what we know, the pathogen forms spores at night and disseminates them at the beginning of day, so that’s when the danger of infection is highest,” said Xinnian Dong, a biologist at Duke University and one of the study’s authors. During the day, when the pathogen does not attack, the genes were not expressed.

This is the first time scientists have made a connection between the circadian clock and pathogen resistance, Dr. Dong said. She believes that if we analyze the complexity of the relationship between pathogens and hosts, and their circadian rhythms, there may be practical applications. Pesticide treatments could be timed to have maximum impact, for instance. Or it may even be possible to determine ideal times for administering medications in humans, she said.

By Sindya N. Bhanoo, www.nytimes.com. Picture by Wei Wang and Xinnian Dong.

Lack of Omega-3 = Depression

Reduced levels of omega-3 in mice had consequences on emotional behaviors, French investigators say. The Institut National de la Santé et de la Recherche Medicale and the French National Institute for Agricultural Research say the imbalanced ratio between omega-6 and omega-3 increased continuously over the course of the 20th century.

The team studied mice fed a permanent diet unstable in omega-3 and omega-6 fatty acids. They found omega-3 deficiency disturbed neuronal communication and the neuronal dysfunction was accompanied by depressive behaviors among the malnourished mice.

"Our results can now corroborate clinical and epidemiological studies which have revealed associations between an omega-3/omega-6 imbalance and mood disorders. To determine if the omega-3 deficiency is responsible for these neuropsychiatric disorders additional studies are, of course, required."

The results give the first biological components of an explanation for the observed correlation between omega-3 poor diets -common in the industrialized world- and mood disorders such as depression.

By UPI.com. No credits for picture.

New Wolf Species in Africa

Conservationists in Egypt have discovered a new species of wolf, which shares DNA with Indian and Himalayan cousins. The "Egyptian jackal", as it's known, is not jackal at all, despite the visual similarities with the golden jackal. The discovery throws light on how wolf species migrated through Africa and Europe - proving that grey wolves emerged in Africa about three million years before they spread to the northern hemisphere.

As long ago as 1880 it had been noticed that the Egyptian jackal looked suspiciously like the grey wolf, and some biologists in the 20th century, studying skulls, made the same observation. However, the creature retained its name. Now, the difference has been formalised.

The investigation is published in the journal PLOS One, with author David Macdonald telling Wired.co.uk in an email: "A wolf in Africa is not only important conservation news, but raises fascinating biological questions about how the new African wolf evolved and lived alongside the real golden jackals."

Eli Rueness of the University of Oslo, who also contributed to the study, added: "We could hardly believe our own eyes when we found wolf DNA that did not match anything." However, the new species' DNA is quite similar to wolves found 2,500 kilometres away in the highlands of Ethiopia.

Professor Claudio Sillero, who has worked in Ethiopia for more than two decades, told Wired.co.uk: "This discovery contributes to our understanding of the biogeography of Afroalpine fauna, a group of species with African and Eurasian ancestry which evolved in the relative isolation of the highlands of the Horn of Africa. Rare Ethiopian wolves are themselves a recent immigrant to Africa, and separated from the grey wolf even earlier than the newly discovered African wolf."

By Duncan Geere in Wired.co.uk. Picture by www.muyinteresante.es.

Good Throwing Saved the Human Species

Homo sapiens are an terribly vain species. We love to exhibit our big brains and our opposable thumbs — and we wouldn't be good for much without them. But there's one human attribute that doesn't get enough attention: the ability to throw things really, really far. According to a new study published in the journal Evolution and Human Behavior, not only was a good arm essential for our early survival, it is also an innate talent, deep into us from the moment of birth.

Humanity's rapid rise to the top on a planet with lots of competing species was never a sure thing. We're slow, we're soft and we have good teeth but they're nothing compared with those of the big cats or the great apes. We needed to kill the predators from a safe distance — first with rocks and later with spears.

"The ability to throw great distances was not a small thing," says Geoffrey P. Bingham, an experimental psychologist at Indiana University. "We are the only animals with that talent." Before we pick something up, we begin tensing muscles in the arm and hand to accommodate the anticipated weight. If that weight is finally less than we guessed, we bring more muscle power to the job than is necessary, making the object feel light.

Projectile selection is a talent that some people have in greater abundance than others. Everyone, however, is born with the basic skill set, and all of us get better with practice. "You acquire the ability at the same time you're learning to throw," says Bingham. That was very good news for your most distant ancestors — and very bad news for a long-ago mastodon.
By Jeffrey Kluger, TIME Magazine. Picture by The Bridgeman Art Library / Getty Images.

The Grandfather of Galaxies

Somewhere out —about 13.2 billion light-years away— the Hubble Space Telescope has recently discovered a magnificent red, amorphous mass. It's a galaxy —or it was— but it is not beautiful, it is magnificently old.

The newly discovered star block — a hundred times smaller than our Milky Way — was formed just 480 million years after the 13.7 billion-year-old universe was born, making it the oldest galaxy. As such, it provides astronomers with a look at the universe in a phase when small galaxies were being formed out of hot gas, only to disappear —leaving the skies free for the immense and mature galaxies that would come along later.

Its size, shape and the era in which it formed all suggest that it began its life as a mass of gas trapped in a pocket of dark matter. In those early days, stars took about 10 times as long to form as they did in later epochs. They were typically part of the blue star class — extremely hot stars, heavy on helium, oxygen and nitrogen. Blue stars last only a few million years before ending their lives in massive explosions.

Soon, stabler stars began to form in much larger galaxies as the universe rapidly cooled. Between 480 million and 700 million years after the Big Bang — when UDFj-39546284 was still in the skies — star formation accelerated. It was then when spiral galaxies and the other glorious formations that define the modern universe appeared.

It is not certain what forces drove those changes. The Hubble Space Telescope has a lot more work to do before more answers are revealed — and a lot more images of thousands of other galaxies to analyze.

By Jeffrey Kluger, TIME Magazine. Picture by NASA.

Health Philosphy

In his book The New Evolution Diet Arthur De Vany, who used to work as a professor at the University of California, argues if we really want to be healthy, we should follow Paleolithic humans' lifestyle. He thinks we should eat low-carb food and exercise intensely in order to control insulin.

De Vany has become the grandfather of the growing Paleo movement, a health philosophy. Their slogan could be reduced to “modern life is simply alien to our genes”. We should return to eat wild animals, fresh produce, eliminate grains and milk, and exercising in intense bursts.

There's no doubt that obesity, heart disease and diabetes are a big problem. And there's no doubt that this is a direct result of our sedentary lives. But there was no Paleolithic "lifestyle." Life in Ice Age Europe was different from life on the African savanna, requiring different diets, behaviors and genetic adaptations. Human DNA evolution didn't stop then. In fact, we're still evolving.

Human genetic adaptations actually increased around 40,000 years ago when we developed technology and became more sophisticated, cooperative thinkers. At least 3,000 significant genetic adaptations have occurred since, including the ability of some Africans, central Asians and northern Europeans to tolerate lactose as adults.

The problem, of course, is that even if De Vany and the other paleo believers are right, there's no going back to the world that existed 40,000 years ago. There's not enough wild animals to feed us all, and our genes don't care how healthy we are, but whether we reproduce or not. From an adaptation perspective, people today are doing really well: there are several billion of us.

From TIME Magazine, by Jennifer Pinkowski. Picture: North Wind Picture Archives / AP Images.

Pet Detective

Your pet already lowers your blood pressure and gives you emotional support. What if it could also identify your colon cancer?

In a new study, a Labrador learned how to sniff out cancer and was able to detect colon cancer. It was nearly as efficient as a colonoscopy. The dog was given breath samples of 306 patients, collected before they received colonoscopies; 48 patients had recently been diagnosed with cancer, and the other 258 were either suffering from another colorectal problem or had survived cancer, or were healthy.

The investigators found that the dog was at least 95% as competent at identifying cancer as colonoscopy when smelling breath samples. But the most important advantage of this technique is that the dog was especially good at detecting early-stage cancer, and could discern polyps from malignancies, which colonoscopies can't do. Detection of early-stage cancers is crucial in bowel cancer diagnosis because surgery can cure almost 90% of patients at an early stage.

Although we will not see the routine use of scent dogs in cancer screening (they're too expensive), this investigation suggests that other methods could be developed to pick up the same scent: a specific cancer smell exists and may become very effective tools.

From TIME Magazine, by Meredith Melnick. Picture by Juliet White/Photographer's Choice via Getty Images.

Mosquitoes and malaria

The discovery of a mosquito that spends most of its time outside could cause problems for malaria control.

In sub-Saharan Africa, malaria kills some 710,000 people each year. The most dangerous form of the disease is caused by a parasite, Plasmodium falciparum, which is transmitted by mosquitoes, mainly of the species Anopheles gambiae. The mosquito larvae live in water, but the adult insects spend much of their time in buildings, where they have human blood. Insecticide sprays, bed nets and access to malaria medication have helped to decrease the number of deaths from malaria.

The newly discovered mosquito group — a subtype of Anopheles gambiae, could be responsible for eradication not being successful. The insects spend their time outside, and then avoid insecticide.

For decades, everybody has thought that the mosquito rests indoors and bites people indoors but collection methods might be wrong. Collecting adult mosquitoes outside is notoriously difficult: traps with artificial bait are inefficient, and using human bait is banned. The aquatic larvae are easier to catch, and they reveal details such as the individual's place of birth. So some larvae were collected and raised to adulthood in the lab.

The scientists tested them for genetic markers and mutations, and compared them with adults caught inside. They found that the indoor insects consisted of two previously known types of Anopheles gambiae. But the outdoor mosquitoes had three distinct types — the two known ones and the previously unknown group. And 58% of new mosquitoes picked up the parasite that transmits malaria, compared with 35% of the indoor mosquitoes.

Extracted from an article by Amy Maxmen in Nature News. Picture by Kenneth Vernick.

Water fleas and toxicity testing

The genome of the water flea Daphnia pulex has been sequenced for the first time. Its DNA contains the largest number of genes ever recorded for a multicellular animal, and could help check the toxicity of chemicals or environmental pollutants without experiments on rats or mice.

Daphnia is a small crustacean found in water all over the world and an important food source for fish. The authors of a study have identified 30,907 genes in its genome; more than one-third of them are not seen in any other organism.

This study is relevant because scientists want to investigate toxins that could be dangerous to the environment or to human health. But until now, studies have been limited to traditional model organisms whose genomes have been sequenced, such as fruit fly (Dosophila melanogaster) or mouse (Mus musculus). This is not so good because the genes considered most important by ecological geneticists are difficult to find in traditional model organisms kept under controlled laboratory conditions. Daphnia, however, is an ecologically-relevant organism that, with the genome in hand, will allow scientists to test the environment.

Daphnia has unusual biology that could be used to get a lot of crucial information. For example, Daphnia eggs can lay dormant in sediments for hundreds of years, so scientists can trace past population-level adaptations to environmental stresses, such as metal toxicities from mining. The crustacean can also clone itself, so ecologists will be able to expose individual genetically identical water fleas to different environmental stressors and track changes in their gene expression.

Extracted from an article by Virginia Gewin in Nature News. Picture by Science/AAAS.

Words and Messages

Longer words carry more information, according to research by cognitive scientists. It might sound obvious, until you start to think about it. Why, then, the difference between short 'now' and long 'immediately'?

For many years, linguists have believed that the length of a word was associated with how often it was used, and that short words are used more frequently than long ones. It was believed that the relationship between word length and frequency of use was based on an impulse to minimize the time and effort needed for speaking and writing.

But Steven Piantadosi and colleagues at the Massachusetts Institute of Technology say that, to give information, it is more efficient to shorten the least informative words, not the most frequent ones. After analyzing word use in eleven different European languages, they found that word length was related with their information content, not with how often they are used.

Measuring the information of a word isn't easy, especially because it can vary depending on the context. The MIT group invented a method for estimating the information content of words in digitized texts by looking at how it is correlated with the preceding words.

But, why do scientists study this? Well, some linguists think language was not born to communicate; in fact, language is about establishing social relations. This study by the MIT is a ferocious counterattack by those who think languages are adapted to deliver information efficiently.

Extracted from an article by Philip Ball in Nature News. Picture by iStockphoto.com/Pgiam.

An Explanation for Mass Extinction

The Permian–Triassic extinction devastated life on Earth 250 million years ago: it killed 96% of marine species and 70% of land-based vertebrate organisms. The reason may have been a volcanic explosion in coal deposits in Siberia. Some days later, ash from the eruption, raining down onto the Canadian Arctic, sucked oxygen from the water and threw toxic elements.

Stephen Grasby, a geochemist, and his colleagues have found three distinct layers of coal ash -fine particles that are freed when coal burns- in rock sediments just before the Permian–Triassic extinction.

 Experts have said for years that volcanoes in Siberian were responsible for the extinction event. There, some rock formations were formed by volcanic activity occurring about the same time as the mass extinction. But with volcanic eruptions so common in history, extra factors must have been involved. In this case, about 500,000–750,000 years before the extinction event, magma went up underground and hit a coal deposit. The mix was explosive and broke the Earth's surface.

Studies have suggested the volcanoes released 3 trillion tonnes of carbon, enough to cause massive climate change. The eruptions also caused acid rain and created an ozone hole. Toxic ash may have been the final blow.

The discovery is so crucial that other studies of extinction events should be examined for the presence of ash.

Extracted from an article by Gayathri Vaidyanathan in Nature News.

Friends connect on a genetic level

Groups of friends show genetic similarity, according to a study that surveyed variation in two out of six genes sampled among friends and strangers. For some geneticists, the conclusion is difficult to believe, because the scientists have not analysed enough genes to be sure that other explanations are impossible.

James Fowler, a social scientist at the University of California, looked at the data on six genes from about 5,000 individuals, and recorded the variation at one specific point, or single nucleotide polymorphism (SNP), in each gene, and compared this between friends and non-friends.

After investigating genetic similarity due to sex, age, race or common ancestry, friends still used to have the same SNP at one position in a gene called DRD2. Friends also showed more variation at one position in the gene CYP2A6 than non-friends.

The ultimate function of DRD2 or CYP2A6 is not clear. But the authors point out that previous studies have associated both genes -controversially- with social behaviour: DRD2 with alcoholism and CYP2A6 with 'openness'. There might be an evolutionary benefit to having friends with compatible genes, even if you don't have children with them. For example, if people who are naturally less susceptible to bacterial infection meet together, their collective health as a group multiplies because the bacteria have no place to live in.

But not everyone is convinced. Because most genes have modest effects on behaviour or health, many scientists think that thousands of SNPs -not only six- need to be analysed before a correlation can be confidently made. 

Adapted from an article by Amy Maxmen in Nature News. Picture by Nana Taimour.

Female tears prevent sex in men.

Women's tears contain chemical signals that reduce testosterone levels in men, according to a study by a neuroscientist in Israel. Testosterone is a hormone found in mammals, reptiles and birds. It is the principal male sex hormone.

The existence of pheromones -chemical signals that produce a social response- in humans has been debated for a long time. Investigation has shown that human sweat communicates information about identity, genetic relatedness, emotional states and health status. Mouse tears contain sex pheromones, but scientists have not previously demonstrated that human crying is a form of chemical communication.

In the study, women watched sad films alone and captured their own tears. Later, 24 men smelled jars containing those women's tears or another substance. Men who sniffed tears judged pictures of women's faces to be less sexually attractive than did the other men. In a separate experiment, 50 men sniffed either tears or the second substance. Smelling tears reduced their sexual response and levels of testosterone in their saliva. The study also exposed 16 men to tears and measured their brain activity using magnetic resonance imaging. Men who sniffed tears showed lower activation in brain regions implicated in sexual arousal.

Robert Provine, who studies the evolution of behaviour at the University of Maryland, says that the results are consistent with previous suggestions that crying could reduce aggression. Testosterone is also responsible for hostility, and reducing aggression could be evolutionarily adaptive.

The results are fascinating. Perhaps more studies on the subject are needed.

Adapted from an article by Janelle Weaver in Nature News. Picture by Punchstock.

Vacunas por decreto

Vacunarse por orden judicial.

Si hacéis un tanteo entre gente menor de 20 años es bastante probable que la mayoría no sepa cuáles son los síntomas del sarampión. Los pocos que lo saben no pasarían la prueba de explicaros además qué ocurre cuando tienes parotiditis y que secuelas puede dejar la rubeola. No es que esta generación esté menos informada en cuestiones de salud que la generación de sus padres, sino que gracias a la vacunación generalizada no han tenido la experiencia de ver a nadie con este tipo de enfermedades infecciosas que antes eran más habituales y que se solucionan con dos dosis de la vacuna llamada triple vírica. Mientras la mayoría de la población esté vacunada el virus no tiene suficientes organismos donde hospedarse y reproducirse. Pero si en una zona concreta muchos padres deciden no vacunar a sus hijos, existe la posibilidad de que se produzca un nuevo brote de una de ellas, con mucha facilidad de sarampión pues es una de las enfermedades más contagiosas que existen.

Esto es lo que ha sucedido en un barrio de Granada, ante lo cual el juez ha decidido obligar- incluso usando la fuerza si fuera necesario- a los padres a vacunar a sus hijos por motivos de salud pública-para proteger a toda la comunidad-aunque sea en perjuicio de los derechos de este grupo de padres. Las asociaciones de vecinos advierten que mientras no se cumpla dicha orden muchas madres no se atreven a sacar a sus bebés de casa por miedo al contagio. Los padres objetores alegan motivos ideológicos y la posibilidad de acogerse a métodos naturales para reforzar el sistema inmunológico de sus hijos. Los médicos de la zona tratan de explicar a la población cuáles son las ventajas médicas de vacunarse, tanto a nivel individual como colectivo.
 
Cada grupo deberá representar uno de los roles y escribir un manifiesto como “comentario” en el blog, que después se expondrá en clase antes de empezar el debate.