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Some chickens have sexual-identity issues, waddling around with half-male and half-female plumage.

Now researchers have figured out the cause of the gender-confusing traits: Half of their bodies are full of female sex cells, while the other half contains mostly male cells.

"This research has completely overturned what we previously thought about how sexual characteristics were determined in birds," said study researcher Michael Clinton of the University of Edinburgh, Roslin, in Scotland. "We now believe that the major factors determining sexual development are built into male and female cells and derive from basic differences in how sex chromosome genes are expressed."

Previously, scientists thought whether an animal became male or female occurred during embryo development when genetic and other factors instructed gonads to become ovaries or testes. These organs, in turn, released hormones that signaled to the brain and reproductive tract, "You are female (or male)." In chickens , those same hormones were also thought to signal gender to tissues that would become feathers and muscles. 

The new research, however, suggests "in birds, sex determination occurs in cells across the entire body, not just in the gonads," Lindsey Barske and Blanche Capel of Duke University Medical Center write in an accompanying perspective article in the same issue of Nature.

In addition to plumage color, the male and female cells also are involved in wattle length (fleshy growth hanging from the head or neck) and comb height.

Sexual identity
In most mammals, including humans, females have two X (sex) chromosomes, while males have one X and one Y. For birds, the sex chromosomes are labeled as Z or W and females have dissimilar chromosomes (ZW), while males have matching ones (ZZ).

Since all the tissues in the body are exposed to the same hormones, the researchers suspected the cells must just respond differently to the hormones. In other words, the body's cells are set in their sexual identity no matter whether they get a squirt of female or male hormones.

"So that made us think the cells must have a sex identity," Clinton said.

The research team included University of Edinburgh scientists Debiao Zhao and Derek McBride.

Female and male cells
To test this idea, they transplanted female chicken cells into a developing male embryo and male cells into a developing female embryo. They did this by inserting the cells into a tiny hole in the eggshell, sealing it up and waiting a week before analyzing the tissues of the developing chicken embryos .

Results showed that ZW donor cells (female) "knew" they were gonads but they didn't get incorporated into the testes, and ZZ donor cells (male) didn't get incorporated into the ovaries and also didn't express the female hormone called aromatase in the host's ovary.

That suggests "their sexual identity was already fixed by the time they arrived in the host tissue," Barske and Capel write.

As for why chickens evolved this system in which sexual appearance is controlled primarily by the sexual identity of cells rather than hormones, Clinton speculates that it's just a simpler system compared with the hormonal one that mammals use.

"We think all birds will be like this, and it's possible other vertebrates will have elements of this system," Clinton told LiveScience.

LANCASTER, Calif. - Authorities say a man was stabbed in the neck with a meat thermometer after asking a woman to silence her cell phone during a screening of the film "Shutter Island" at a Southern California movie theater.

Los Angeles County sheriff's spokesman Steve Whitmore says the stabbing happened Feb. 27 during a screening of the Martin Scorsese film in Lancaster. He says the two suspects remain at large.

Whitmore says the victim had complained about a woman sitting nearby who was talking on her phone during the movie. He says the woman left with two men, but the men returned minutes later and stabbed the victim in the neck.

Two other people in the theater came to the victim's aid and also were hurt. The man was hospitalized with serious injuries.

The sheriff's office says it knew the weapon used was a meat thermometer because the suspects left it behind. No further details were released.

WELLINGTON, New Zealand - The rare spirits that went under the gavel at a recent online auction in New Zealand weren't aged brandies or hard-to-find liqueurs.

Instead, two glass vials purportedly containing the ghosts of two dead people sold for $2,830 New Zealand dollars ($1,983) at an auction that ended Monday night.

The "ghosts" were put up for bidding by Avie Woodbury from the southern city of Christchurch. She said they were captured in her house and stored in glass vials with stoppers and dipped in holy water, which she says "dulls the spirits' energy."

She said they were the spirits of an old man who lived in the house during the 1920s, and a powerful, disruptive little girl who turned up after a session with a spirit-calling Ouija board. Since an exorcism at the property last July led to their capture, there has been no further spooky activity in the house, she said.

The auction attracted more than 214,000 page views and dozens of questions before the winning bid, Trademe auction site spokesman Paul Ford said Tuesday. The name of the winning bidder was not released.

Woodbury said that once an "exorcist's fee" has been deducted, the proceeds of the spirit sale will go to the animal welfare group the Society for the Prevention of Cruelty to Animals.

WELLINGTON, New Zealand - The rare spirits that went under the gavel at a recent online auction in New Zealand weren't aged brandies or hard-to-find liqueurs.

Instead, two glass vials purportedly containing the ghosts of two dead people sold for $2,830 New Zealand dollars ($1,983) at an auction that ended Monday night.

The "ghosts" were put up for bidding by Avie Woodbury from the southern city of Christchurch. She said they were captured in her house and stored in glass vials with stoppers and dipped in holy water, which she says "dulls the spirits' energy."

She said they were the spirits of an old man who lived in the house during the 1920s, and a powerful, disruptive little girl who turned up after a session with a spirit-calling Ouija board. Since an exorcism at the property last July led to their capture, there has been no further spooky activity in the house, she said.

The auction attracted more than 214,000 page views and dozens of questions before the winning bid, Trademe auction site spokesman Paul Ford said Tuesday. The name of the winning bidder was not released.

Woodbury said that once an "exorcist's fee" has been deducted, the proceeds of the spirit sale will go to the animal welfare group the Society for the Prevention of Cruelty to Animals.

Just past Dracula’s castle, deep within Romania’s Carpathian Mountains, the Transfagarasan Highway is a 55-mile stretch of roadway so scenic and wickedly winding that it rendered Jeremy Clarkson  glib host of the BBC’s popular automotive show "Top Gear" practically speechless. That ‘s no small feat, since for more than 20 years, Clarkson has made it his business to bomb around the world’s most breathtaking roads.

Surveying the twisted tarmac zigzagging below its summit from the cockpit of his Aston Martin DBS, he chuckled with pure delight, exclaiming to the camera, “That’s the most amazing road I’ve ever seen!” If he’d had a tail, it surely would have been wagging.

This serpentine motorway is just one of many mind-bogglingly crazy roads around the globe. And these exciting — albeit potentially perilous — paths offer travelers a refreshing diversion in an era of monotonous interstates and traffic-controlling roundabouts.

From the seemingly insurmountable Alps to the craggy coastline of the Amalfi, the steep hills of New Zealand to the arctic expanses of northern Canada, dramatic geography has left us with some of the world’s more brilliantly engineered pieces of pavement.

Or not so brilliantly engineered. Take, for instance, Bolivia’s ill-conceived Yungas Road, a rickety route connecting the high-altitude capital of La Paz with the low-elevation rainforest town of Coroico. This dangerous pass poses such a harrowing journey (largely unpaved, single lane, no guardrails, 2,000-foot drops) that it claims an estimated 200 drivers  lives annually, rightfully earning it the nickname El Camino de la Muerte (“The Road of Death”).

Back in Romania, the  Transfagarasan ’s own bloody history began with its creation. Built in the 1970s under President Nicolae Ceauescu as a means to mobilize armed forces in the event of a Soviet invasion, this roadway —connecting the remote regions of Transylvania and Wallachia in an endless series of bends, tunnels, and viaducts  exists at the cost of six thousand tons of dynamite and 40 road workers’ lives. Dracula might have approved, but to this day locals bitterly refer to the highway as Ceau?escu’s Folly.

Given those figures, Bolivian bus tours and Transylvanian road trips might not top your to-do list. But the next time you’re zoning out in cruise control or find yourself verbally engaging the Garmin GPS’s female navigator just to stay awake, think of the demanding, dangerous, and downright crazy roads ahead. Then thank your lucky stars for the carpool lane.