9 Things We Learned About Us in 2009
LiveScience looks back at 9 new things we learned about us in 2009.
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For a species that has been studying itself for thousands of years, you might think humans would have learned everything there is to know about, well, us. But science never ceases to reveal more about the complex human body, mind and culture. Here are 9 of the most fascinating things we learned about ourselves in 2009:  

Adults have baby fat. Scientists had long believed the brown fat that babies are born with disappears once they grow up. But a study published this year in the New England Journal of Medicine showed that some adults do indeed retain deposits of this baby fat. And this is the so-called good fat since it burns calories. In fact, the researchers also found that thinner people are more likely to have brown fat, suggesting that it may play a role in regulating body weight. Boosting growth of this fat could potentially become a new way to treat obesity, the researchers said.

Your skin is loaded with bacteria. Scientists are learning more and more about the many bacteria that reside in and on our bodies through the Human Microbiome Project. New results this year showed that different populations of bacteria inhabit different sites on our skin, with some sites more diverse than others. The forearm was the winner in terms of diversity, with scientists finding 44 different bacterial species there.

Late-sleepers are more alert than early-risers. "Morning people" may get out the door earlier, but at a price: They may not stay focused as long as those who stay up late and stay snuggled beneath the covers during the a.m. hours, according to a study that examined the attention spans of both early birds and night owls. The study measured the alertness of both groups at 1.5 hours and 10.5 hours after waking. Results showed that while both groups had about the same attention level at 1.5 hours, the late-sleepers were more focused than the early-risers after 10.5 hours. So if you find yourself naturally rising at dawn, you may want to think twice before scheduling an important afternoon meeting.

Could you speak into my right ear please? If you want someone to do you a favor, you may be better off speaking into their right ear than their left, a study this year suggests. The results showed that people would rather be addressed in their right ear, and they are also more likely to grant favors if the appeal is made to the right ear. This preference may be due to the fact that speech coming into the right ear is mostly processed by the left side of your brain, the hemisphere that is thought to process verbal information.

Multitasking slows you down. If you do a lot of multitasking, you should be good at it, right? Not so, according to research out this year that found those who multitask more frequently are actually worse at it than those who conquer chores individually. In the study, multitaskers took longer to complete tasks, and when they had to switch tasks, they were slower at it. The findings add more evidence to the argument that certain multitasking situations, such as texting while driving, may not be wise, and even can be dangerous.

Infants cry in their native tongue. Even when babies are only a few days old, their cries resemble their native language, researchers in Germany found this year. For instance, the cries of French infants have a rising melody pattern from start to finish — a characteristic of the French language. On the other hand, German infants have cries with falling melodies — a pattern found in German speech.   

Most children lack vitamin D. A national survey of U.S. children showed that about 70 percent do not have sufficient levels of vitamin D, a result the researchers deemed "shocking." They pinned the blame for the low vitamin levels on poor diet and too little sunshine. Vitamin D deficiency can put people at risk for bone disorders, such as rickets, as well as heart disease. So, perhaps, a New Year's resolution to get the kids outdoors may be in order.

Cohabiting before marriage may lead to divorce. Moving in with your significant other before marriage may not be the best idea, say researchers at the University of Denver. Their survey found that people who cohabited before wedding were more likely to report a lower quality of marriage, and these couples were more likely to split than those who held out on living together until after they tied the knot.

Why you aren't born walking. Scientists think they know why some animals, such as horses and giraffes, can get up and walk only hours after being born, while humans take about a year before they can move upright on two legs. Although mammals seem to start ambling at different points in their childhood, they actually begin to walk at the same point in their brain development, according to a study released this month.