Hello, I'm Hank Green and this week in Sci Show News we're up to our elbows in the science of weird disorders and strange behaviors including a chemical that makes men stay faithful, new insights into what makes some behavior contagious and in response to your requests the truth about a disease that makes people allergic to meat.  
 
Who's hungry?

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Lets start with perhaps the most inscrutable behavior of them all, mating behaviors. Scientists think that they've identified a hormone that makes men faithful to their partners. Let me say it again, there is a hormone that makes men not want to have sex with other attractive women.  
 
German scientists - of course they're German- reported this week that heterosexual men in committed relationships become uncomfortable around women that they find attractive after they had been given a dose of the hormone oxytocin.
 
Oxytocin is a hormone that in women stimulates contractions during childbirth and triggers the production of breast milk; it's sometimes known as the "nurturing hormone" for this reason, but it's affect on men is less clear.
 
In the new study done in the University of Bonn, researchers gave either oxytocin or a placebo to two groups of  committed, straight men. Forty-five minutes later, the men were introduced to a female experimenter that these subjects described as hothothothothot.
 
The experimenter then moved closer to the subjects and the men were asked to indicate how comfortable they felt and respond accordingly. The married men given the hormone moved away from the woman while the ones given the placebo as well as single men tested in a separate experiment were perfectly happy to be closer.
 
What surprised scientists is that oxytocin is thought to stimulate intimacy and trust among people, not unease. So what’s the secret? Well, it turns out that men are basically no different from prairie voles. 
 
Previous research on voles--which if you don't know, are like mice but more adorable--has shown that oxytocin plays a key role in monogamist behavior in males. As with females it seems to influence behavior that helps keep family bonds strong.

So, does that mean we've found a drug that keeps men from acting like philandering jerks? I can think of some women who wouldn't be opposed to that, including at least a couple who are on close, personal terms with David Petraeus.

But science can only do so much, people. The German scientists conclude that men's ability to remain faithful, regulated in part by their levels of oxytocin, is a biological trait that humans have retained throughout their evolution from the earliest mammals. The research was published in this week's issue of the Journal of Neuroscience, and you can find it in the links below.

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While we're talking about why we really do stuff, let's look at two new insights into why behavior becomes contagious.

Yawning is probably the most famous form of contagious behavior; when you see someone yawn, you usually do it, too. It's such a wide-spread reflex that the inability to yawn when someone else does has been used as an indicator for neural disorders, like autism.

Why we do this isn't really clear, though there are lots of theories that sometimes are taught as facts.

So this week, we learned that the reflex goes back very far in our evolutionary history. In the journal PLLS1 a pair of Italian biologists said that they'd documented contagious yawning in Bonobos, the great apes that are closely related to chimps, and to us.

While studying Bonobos in captivity, the scientists found the apes regularly yawned within a minute of seeing another ape do the same. What's more they found that the reflex was much more contagious among individuals that shared close personal bonds, especially family members than among apes from different groups.

This mirrors the responses seen in humans who are more apt to yawn when they see a friend or family member do it than when they see a stranger do it.

None of this sheds a lot of light on what if any evolutionary purpose contagious yawning might have, but researchers say the cause might be purely emotional.

Responding physically to some one else's physical behavior is a sign, they said, of empathy. The ability to share an emotional state with some one else, which reinforces all important social bonds.

But you know what behavior is definitely totally useless but we can't help doing anyway? I mean, besides from watching reality TV? Contagious itching.

Believe it or not,  a team of British scientists has put a lot of time and thought into the study of why people suddenly feel itchy when they see someone else scratching themselves.

In the journal PNAS psychologists say that they showed videos to 51 volunteers of people either scratching themselves or just tapping their arms and legs. About 65% of the subjects who saw the scratching videos started scratching themselves. Which, the scientists say, makes itching  the most contagious behavior ever measured. More than yawning which averages 50% of people, or laughter, at 47%.

They also used questionnaires and other tools to conduct personality tests of the subjects and found that the ones that reacted most strongly to the contagious itching also scored the highest for neurosis, which they define as a tendency to experience negative emotions.

So the psychologists say, itching may be a whole different glass of so called social contagion. More contagious than other behaviors, but also more likely to turn into compulsion, unlike yawning and laughing.

And now, all across this great nation that is the viewers of SciShow, you're all yawning and scratching yourself.

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Finally, the weirdest disorder you'll hear about this week, I hope. Some of you have been asking to learn more about a strange new disease that's gotten some attention lately. A vector born disease that causes a sudden and severe allergy to meat.

The media, ever so good at headline writing are describing it as a kind of reverse zombie plague that turns people into vegetarians. Well I've looked into it, and, brace yourself, it's kinda true.

The condition was first reported last year, but it wasn't until July that the mystery behind it finally seemed to be solved, by one Dr. Susan Wolver and her colleagues at Virginia Commonwealth University.

After investigating several strange cases of people in the southeastern United States going into unexplained allergic shock, they determined that all of the patients had 2 things in common. They had all eaten red meat and had all been bitten by or lived in the range of a kind of arachnid found in the south called the lone star tick.

It turns out that the saliva of this tick contains a sugar that's also found in certain kinds of meat. A sugar, known as alpha-gal is produced by most mammals, like cows and pigs and deer, but not by primates. We humans cannot make it on our own.

The tick bite caused the patients' immune systems to form antibodies to this new sugar and as a result, whenever people ate meat, their natural defenses started to attack the alpha-gal, that they had ingested from the meat. 

And the unholy terror that their immune systems unleashed caused some pretty severe symptoms, like hives, difficulty breathing, swollen tongue, and like I mentioned, shock.

Unlike other tick-borne diseases, like Lyme disease, this condition appears to be permanent, and untreatable. Patients can still eat the meat of non-mammals, like chicken, turkey, and fish, so they're not doomed to a life of vegetarianism, if you were worried about that.

Still, the disease is one for the record books. It's the first known allergy to be transmitted by an animal bite. It's also the only food allergy that's triggered by a sugar instead of a protein.

The interesting thing here, is that if the world suddenly, you know, came down with this disease, on a planet-wide scale, that might not be a good thing for like, dairy farmers and people who really like red meat, but it would be a good thing for the earth as a whole.

If you want to learn more about the tremendous impact that eating red meat has on the world, you can check out our over-population video. 

A fascinating conundrum. I know that here in Montana it would kind of destroy the economy, so I'm not really sure where I come down on this.

If you could infect the entire world with this disease, would you do it? I'm curious, down in the comments. And if you have any other comments or questions or ideas, we're on Facebook and Twitter, and of course down in the comments below.

And if you want to keep getting smarter with us here at SciShow, you can go to https://youtube.com/scishow and subscribe.

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