The first reptile with a true placenta

In evolution, as in life, some things are easier than others. It seems to be pretty straightforward to evolve complex eyes, which have turned up dozens of times.

Similarly, for some groups of animals it's easy to stop laying eggs and start giving birth to live young. Backboned animals have evolved live birth no fewer than 132 times, and nowadays a fifth of lizards and snakes give birth. Human mothers may disagree, but live birth is clearly not that difficult.

What is difficult, however, is nourishing unborn young the way mammals do. A female mammal allows each embryo to burrow deep into the wall of her womb, where it takes nutrients straight from her blood. This intimate arrangement was long thought to have only evolved once, in mammals.

Not so. It now appears that it evolved at least twice: once in mammals, and once in an obscure African lizard called Trachylepis ivensii.

Ancient cave paintings threatened by tourist plans

Prehistoric paintings in northern Spain could be irreparably damaged if plans to reopen the Altamira cave to tourists go ahead. Local officials want to reopen the cave to boost the local economy, but visitors could heat the caves and introduce microbes that destroy pigments.

The Altamira cave paintings were discovered in 1879 and are thought to be at least 14,000 years old. The paintings have attracted huge numbers of visitors – 175,000 in 1973, the busiest year on record. But the cave was closed to the public in 2002 after photosynthetic bacteria and fungi were found to be consuming pigments at alarming rates.

Plans to reopen the caves could restart the damaging processes. A team from the Spanish National Research Council in Madrid have modelled the effect of visitors over a number of years and say that tourists would increase the temperature, humidity and carbon-dioxide levels in the cave, creating conditions in which microbes would thrive.

In addition, visitors would bring with them organic matter in the form of skin flakes, clothing fibres and dust, which microbes can consume. Air turbulence created by moving people would spread bacterial and fungal spores to other, previously unaffected spaces.

Diabetic rats cured with their own stem cells

A cure for diabetes could be sitting in our brains. Neural stem cells, extracted from rats via the nose, have been turned into pancreatic cells that can manufacture insulin to treat diabetes.

Beta cells in the pancreas produce insulin, which regulates glucose levels. People with diabetes either have type 1, in which native beta cells are destroyed by the immune system, or type 2, in which beta cells cannot produce enough insulin.

To replace lost or malfunctioning beta cells, Tomoko Kuwabara of the National Institute of Advanced Industrial Science and Technology in Tsukuba Science City, Japan, and colleagues turned to neural stem cells in the brain.
First, they extracted a tiny amount of tissue from the rats' olfactory bulb, the part of the brain which deals with smell, or from the hippocampus, involved in memory. Each area is accessible through the nose, both in rats and humans.

Next, the team extracted neural stem cells from the tissue and exposed them to Wnt3a – a human protein that switches on insulin production – and to an antibody that blocks a natural inhibitor of insulin production.

After multiplying the stem cells for two weeks, they placed them on thin sheets of collagen which act as a removable scaffold. This allowed the team to lay the sheets incorporating the cells on top of the rats' pancreas without harming the organ itself.

Within a week, concentrations of insulin in the blood of both type 1 and type 2 rats that had received treatment matched those in non-diabetic rats. Elevated blood glucose concentrations also returned to normal.

The cells successfully tackled diabetes for 19 weeks until researchers halted the treatment by removing the sheets of cells, after which the rats' diabetes returned.

Russian tigers threatened by dog disease

Wild Amur tigers in Russia are falling victim to a viral infection transmitted by stray dogs. The same disease has taken its toll on the lions of the Serengeti, and a mutated version threatens seals around the world. However, vaccination could halt the spread of the virus.

Over the past decade there have been two confirmed cases of Siberian tigers falling victim to canine distemper. The virus causes muscle twitching and confusion, and eventually fatal seizures.

In November 2003 a wild tigress wandered into the village of Pokrovka in Khabarovskiy Krai in the far east of Russia. She was captured by Wildlife Conservation Society staff and treated, but died in captivity (Journal of Wildlife Diseases, vol 46, p 1252). Then last year another tigress entered a different village, Terney. She was shot dead by local police after repeated attempts to capture her failed.

Samples from the two tigers confirm that they were carrying the distemper virus, says Denise McAloose of the Wildlife Conservation Society in New York. McAloose is studying samples from four more Amur tigers that showed similar symptoms, and suspects that some will also turn out to have had distemper. She presented her findings at an international symposium devoted to the International Year of Forests in Ussuriysk, Russia.

Why size matters in the plant world too

Over 60 years ago, evolutionary biologist Bernhard Rensch calculated that males are typically the larger sex in big-bodied species such as humans, whereas females outdo them in small-bodied species such as spiders. Now it turns out that many plants obey Rensch's rule too.

Most plants produce both male and female sex organs, but around 7 per cent are dioecious, meaning individuals are purely male or female. Kevin Burns and Patrick Kavanagh at Victoria University of Wellington in New Zealand measured the leaf and stem sizes of 297 plants from 38 dioecious plant species in herbarium collections of the National Museum of New Zealand and discovered that they follow the sex-size rule.

Why? "Females need to hold the seeds and the fruit," Burns says, adding that female stems also must be large enough to display the fruit and support the animals that spread the pollen or seeds. If metabolism, predators or climate promote the evolution of smaller plants, however, males can shrink because their gametes are smaller.

The sticky bit, says Burns, is why males produce larger leaves in bigger species. Martin Burd at Monash University in Melbourne, Australia, says Rensch's rule can be explained in animals because males compete for females and often the larger fellows win.

"It's possible that successful male plants produce larger flowers or more flowers to attract more pollinator visits," says Burd. Bigger stems and leaves would therefore be needed support the floral display, but this needs to be tested, he adds.

Size might not be the only such gambit adopted by plants and animals to successfully reproduce. Burd has preliminary evidence that both birds and plants evolved similar tactics – of cramming flowers with ovules or increasing egg number per nest – to capitalise on unpredictable changes in their food supply.

New Aurora Pictures

Green auroras illuminate the sky over Whitehorse, in Canada's Yukon Territory, on Monday.

Such auroral displays are triggered when clouds of charged particles from the sun—known as coronal mass ejections (CMEs)—slam into Earth's magnetic field.

A "severe" CME hit September 26, sparking auroras at both Poles and inducing light shows visible in five U.S. states, including Michigan, New York, South Dakota, Maine, and Minnesota, according to NASA.

As solar particles get funneled along Earth's field lines toward the Poles, they collide with molecules in the atmosphere, infusing them with extra energy. The molecules in turn release the energy as light.

Capturing the above aurora required "a long night of waiting-but the activity picked up," photographer Jonathan Tucker wrote on

Physics Nobel Explainer: Why Is Expanding Universe Accelerating?

New Nobel laureates Saul Perlmutter and Adam Riess of the U.S. and Brian Schmidt of Australia contributed to the discovery that the universe is not only expanding but also speeding up.

The finding led to the now widely accepted theory of dark energy, a mysterious force that repels gravity. Measurements show that dark energy accounts for about 74 percent of the substance of the universe.

But more than a decade after the Nobel-worthy find, scientists are still trying to pin down exactly what dark energy is and and thus solve what some experts call "the most profound problem" in modern physics.

(Also see "New Galaxy Maps to Help Find Dark Energy Proof?")

Does Gravity Work Differently?

Until dark energy, physicists were convinced that gravity should be causing the expansion rate of the universe to slow.

"When I throw my keys up in the air, the gravity of the Earth makes them slow down and return to me," said Mario Livio, a theoretical physicist at the Space Telescope Science Institute (STScI) in Maryland, said during the Decade of Dark Energy Symposium, held in 2008.

But by studying the light from distant supernovae, astronomers saw that the supernovae's host galaxies are flying away from each other at increasing speed.

The observation that the universe's expansion rate is actually speeding up, Livio said, is as if "the keys suddenly went straight up toward the ceiling."

So far, one of the biggest challenges for dark energy researchers is marrying observations to theory.

"We have two known, totally unsatisfactory explanations," said Michael Turner, a cosmologist at the University of Chicago.

One possibility is there is no dark energy, and gravity works differently than scientists think.

(See "Dark Energy's Demise? New Theory Doesn't Use the Force.")

But "physicists are conservative. We don't want to throw away our theory of gravity when we might be able to patch it up," Nobel co-winner Riess, an STScI cosmologist, told National Geographic News.

"Basically it all comes down to the fact that there's one relatively simple equation we work with to describe the universe," Riess said.

"Because we see this extra effect, we can either blame it on the left-hand side of the equation and say we don't understand gravity, or we can blame it on the right-hand side and say there's this extra stuff."

Dark Energy a Product of Quantum Vacuum?

The extra stuff—and a leading contender for explaining dark energy—is quantum vacuum energy.

The idea is tied to quantum mechanics, which predicts that even in the vacuum of space, particles are constantly winking in and out of existence, generating energy.

(Related: "Dark Matter Is an Illusion, New Antigravity Theory Says.")

The trick is that no one has been able to unify the math used in quantum mechanics, which describes the physics of the very small, with the equations in general relativity, which deal with large-scale interactions.

"The two theories use two different sets of rule books, [and] we've always known that these two books are incompatible," Riess said.

Unfortunately, "dark energy is one of the few cases in nature that really requires us to [somehow] use both sets of rules."