For centuries people have pondered the meaning of dreams. Early civilizations thought of dreams as a medium between our earthly world and that of the gods. In fact, the Greeks and Romans were convinced that dreams had certain prophetic powers. While there has always been a great interest in the interpretation of human dreams, it wasn't until the end of the nineteenth century that Sigmund Freud and Carl Jung put forth some of the most widely-known modern theories of dreaming. Freud's theory centred around the notion of repressed longing -- the idea that dreaming allows us to sort through unresolved, repressed wishes. Carl Jung (who studied under Freud) also believed that dreams had psychological importance, but proposed different theories about their meaning.

Since then, technological advancements have allowed for the development of other theories. One prominent neurobiological theory of dreaming is the "activation-synthesis hypothesis," which states that dreams don't actually mean anything: they are merely electrical brain impulses that pull random thoughts and imagery from our memories. Humans, the theory goes, construct dream stories after they wake up, in a natural attempt to make sense of it all. Yet, given the vast documentation of realistic aspects to human dreaming as well as indirect experimental evidence that other mammals such as cats also dream, evolutionary psychologists have theorized that dreaming really does serve a purpose. In particular, the "threat simulation theory" suggests that dreaming should be seen as an ancient biological defence mechanism that provided an evolutionary advantage because of its capacity to repeatedly simulate potential threatening events - enhancing the neuro-cognitive mechanisms required for efficient threat perception and avoidance.

So, over the years, numerous theories have been put forth in an attempt to illuminate the mystery behind human dreams, but, until recently, strong tangible evidence has remained largely elusive.

Whale-watching tourists off western Australia saw more than they expected - and perhaps more than many of them wanted - last week. As two boats of observers took in the action, a humpback whale mother desperately and vainly tried to protect a calf from four predatory orcas.

The video below, shot from a light aircraft that circled overhead as the action unfolded, isn't always easy to make out, but it shows the orcas circling as the humpback attempts to protect the calf by lifting it on to her back. (If you pause the video at about 12 seconds, you can see the whale more or less center of the screen, and the lighter-colored calf just above it.)

According to witnesses, the humpback was spotted with two calves, but the orcas swiftly came on the attack taking one. The mother only succeeded in protecting her second calf for about three-quarters of an hour before it, too, succumbed to the ambush:

"I've been diving for three years and I've never seen anything like it," said Tamar Melen, who watched the 45-minute spectacle unfold metres from the boat. Sadly, the killer whales made off with both calves. Ms Melen, 31, said they grabbed the first in seconds, but the attack on the second lasted half an hour. "It was quite impressive," Ms Melen said. "The first hit was so quick, but then they took their time with the second. It was agonising to watch the mother humpback trying to protect her calf.

A lethal bat-borne horse virus has been detected in a dog for the first time, authorities in Australia said on Tuesday, prompting fears it has jumped species.

"This is the first time outside of a laboratory that an animal other than a flying fox or a horse, or a human, has been confirmed with Hendra virus infection," Queensland state Chief Veterinary Officer Rick Symons said.

So far, 14 horses have died or been put down in Australia since June as a result of the Hendra virus, which was only discovered in 1994.

No humans have yet been infected in the current outbreak, which has affected farms in New South Wales and Queensland, but four of the seven people ever to have contracted the disease have died.

For an opinion or belief, 10 percent is critical mass. If that proportion of the population emphatically embraces an idea, then it will spread rapidly to the majority of the population, scientists have found.

"When the number of committed opinion holders is below 10 percent, there is no visible progress in the spread of ideas," said researcher Boleslaw Szymanski, director of the Social Cognitive Networks Academic Research Center at Rensselaer Polytechnic Institute. "Once that number grows above 10 percent, the idea spreads like flame."

For example, dictators who held power for decades in Tunisia and Egypt were overthrown in a matter of weeks when events pushed public opinion past the 10 percent threshold, Szymanski said.

Radioactivity and gravity may be why the strange football-shaped dwarf planet known as Haumea and its moons are unexpectedly sheathed in crystalline ice, shining in space, researchers suggest.

Haumea, named after the Hawaiian goddess of childbirth, orbits the sun beyond the path of Neptune, with two moons in orbit around it named Hi'iaka and Namaka, two of the deity's daughters.

Haumea is a bizarre dwarf planet world shaped like a cigar, or perhaps an American football, measuring about 1,200 miles (2,000 kilometers) long, and makes one full rotation in less than four hours. This is one of the fastest rotation speeds in the solar system, which gave Haumea its odd shape.

Now, surprisingly, an international research team has discovered that 75 percent of Haumea's surface is covered with crystalline water ice.

The human brain is big, and it's powerful, able to dream up innovative solutions to complex problems. Yet our brains don't age well: As we grow older, they tend to shrink and become increasingly vulnerable to cognitive dysfunctions such as memory loss and dementia. A new magnetic resonance imaging (MRI) study comparing humans and chimpanzees finds that chimp brains maintain their size as they age. Slowly losing our minds, it turns out, may be the evolutionary price we pay for having bigger brains and longer life spans.

As far as researchers can tell, humans are the only animals subject to specific brain maladies such as Alzheimer's disease, which in the United States afflicts nearly 50% of people over the age of 85. But even normal, apparently healthy human brains show the effects of aging, such as the buildup of amyloid-β plaque deposits and loss of neural connections, especially in regions linked to learning and memory. And previous studies of human brains have suggested that these brain regions, which include the frontal lobe and the hippocampus, are especially prone to shrinkage with age.

Although few similar studies of other primates have been conducted, recent research with rhesus monkeys has shown only very limited shrinkage with age. Nevertheless, the evolutionary lineages leading to humans and rhesus monkeys diverged about 30 million years ago, leaving scientists in the dark about when the human pattern of brain aging might have begun.

Scientists engaged in the search for extraterrestrial intelligence (SETI) work under the assumption that there is, in fact, intelligent life out there to be found. A new analysis may crush their optimism.

To calculate the likelihood that they'll make radio contact with extraterrestrials, SETI scientists use what's known as the Drake Equation. Formulated in the 1960s by Frank Drake of the SETI Institute in California, it approximates the number of radio-transmitting civilizations in our galaxy at any one time by multiplying a string of factors: the number of stars, the fraction that have planets, the fraction of those that are habitable, the probability of life arising on such planets, its likelihood of becoming intelligent and so on.

The values of almost all these factors are highly speculative. Nonetheless, Drake and others have plugged in their best guesses, and estimate that there are about 10,000 tech-savvy civilizations in the galaxy currently sending signals our way - a number that has led some scientists to predict that we'll detect alien signals within two decades.

The old adage "Looks can be deceiving" certainly rings true when it comes to people. But it is also accurate when describing special light-sensing cells in the eye, according to a Johns Hopkins University biologist.

In a study recently published in Nature, a team led by Samer Hattar of the Department of Biology at the Krieger School of Arts and Sciences and Tudor Badea at the National Eye Institute found that these cells, which were thought to be identical and responsible for both setting the body's circadian rhythm and the pupil's reaction to light and darkness, are actually two different cells, each responsible for one of those tasks.

"In biology, as in life, you can't always trust what you see," said Hattar. "You have to delve deep to find out what's really going on. This study has shown that two structurally similar neurons are actually quite different and distinct, communicate with different regions of the brain and influence different visual functions."

The findings are significant, Hattar said, because doctors sometimes use pupillary light reflex (the pupil's response to light and darkness) as a way of diagnosing patients who may have sleep problems, and those clinicians now must recognize that the cells controlling pupillary response and those controlling the sleep-wake cycle are different.

And with no Scotty to beam them up, allocated 15-year time looks daunting

Houston: With the space shuttle now history, NASA's next great mission is so audacious, the agency's best minds are wrestling with how to pull it off: Send astronauts to an asteroid in less than 15 years.

The challenges are innumerable. Some old-timers are grousing about it, saying going back to the moon makes more sense. But many NASA brains are thrilled to have such an improbable assignment. And NASA leaders say civilization may depend on it.

An asteroid is a giant space rock that orbits the sun, like Earth. And someday one might threaten the planet.

But sending people to one won't be easy. You can't land on an asteroid because you'd bounce off - it has virtually no gravity. Reaching it might require a NASA spacecraft to harpoon it. Heck, astronauts couldn't even walk on it because they'd float away.

The development of a new cell-culture system that mimics how specific nerve cell fibers in the brain become coated with protective myelin opens up new avenues of research about multiple sclerosis. Initial findings suggest that myelin regulates a key protein involved in sending long-distance signals.

Multiple sclerosis (MS) is an autoimmune disease characterized by damage to the myelin sheath surrounding nerve fibers. The cause remains unknown, and it is a chronic illness affecting the central nervous system that has no cure.

MS has long been considered a disease of white matter, a reference to the white-colored bundles of myelin-coated axons that project from the main body of a brain cell. But researchers have discovered that the condition also affects myelinated axons scattered in gray matter that contains main bodies of brain cells, and specifically the hippocampus region, which is important for learning and memory.