Along with some truly groundbreaking discoveries, scientists this year told us a few things we already kind of knew.

Here are some of the ultimate "well, duh" findings of 2010:

Meth can harm an unborn child.

Turns out, it's not a great idea for a gal with a bun in the oven to shoot up with methamphetamine. The study, published in the March 17 issue of The Journal of Neuroscience, showed children whose moms abuse meth while pregnant had brain abnormalities that were possibly more severe than those of kids exposed to alcohol prenatally. Perhaps not everyone was aware: Of the more than 16 million Americans over the age of 12 who have used meth, about 19,000 are pregnant women, according to data from the National Surveys on Drug Use and Health.

But wait, there's some substance here: Identifying the vulnerable brain structures may help predict particular learning and behavioral problems in meth-exposed children, the researchers said.

Bullies pick on unpopular kids.

Who'd have guessed? Bullies target kids who are unpopular and less likely to be defended by their peers, a new study finds.

And in elementary school, which this study focused on, kids are only interested in what their same-sex peers think. So, boys will target classmates who are not well-liked by other boys, regardless of what the girls think. Same went for girl bullies. In that way the bullies could gain status by dominating other kids while also staying in the good graces of the in-group.

While the findings are a no-brainer, they do paint a picture of a young, yet strategic, bully who goes out of his or her way to ensure success when taunting, hitting, making fun of and other bully behaviors.

"Bullies do it so strategically that if there is not a good program at the school nothing will change. They won't change their behavior by themselves, because it gives them a lot of advantages," said lead researcher René Veenstra, professor of sociology at the University of Groningen. "You really need a good program that changes the attitude of all the kids in the classroom that makes clear to children that if they want the bully to stop they all have to be part, take joint action." Veenstra and colleagues detailed their findings in the March/April issue of the journal Child Development.

Smoking a lot of weed is bad for you.

Marijuana use can cause mess up your head, suggests a study presented this year at the meeting for the Society of Neuroscience. Results showed the more marijuana a person used the greater difficulty they had in focus and attention

In the study, participants had to complete a card-sorting task in which they were shown four cards that differed in color, symbol and value. Based on the rules they gleaned from the displayed cards, they had to sort a deck of cards. Participants were only told whether their sorting attempts were correct or not. Habitual marijuana users made repeated errors despite feedback that they were wrong. Marijuana users also had more difficulty maintaining a set of rules when sorting, suggesting an inability to maintain focus.

Those participants who began using marijuana before the age of 16, and those who used the most marijuana, showed the greatest impairment.

Friendless kids are sad.

That's essentially what a three-year study of 130 girls and 101 boys in third through fifth grades found. Compared with friendless children, those who had pals were less likely to report depressed feelings. Particularly for those shy and withdrawn kids, having a friend seemed to stave off the blues.

"Having one friend can be protective for withdrawn or shy kids," said lead author William M. Bukowski, a psychology professor and director of the Concordia Centre for Research in Human Development. "Our study confirms the value of having friends, which are like a shield against negative social experiences."

Guys prefer casual sex to dating.

Why in the world would a guy rather have a fling than a series of dates where commitment may be involved? A study out this year in the journal Sex Roles suggests it comes down to context.

While overall numbers showed both genders preferred traditional dating to hooking up, of those college students who strongly preferred traditional dating, there were significantly more women than men (41 percent versus 20 percent). Of those who preferred casual sex, there were far fewer women than men (2 percent versus 17 percent).

When participants were asked to consider the possibility of a long-term relationship, both guys and gals preferred dating over hooking up. However, when that relationship possibility wasn't mentioned, men chose hooking up and women dating. Guys also indicated that even with hook-ups (which are meant to be string-free), they feared their casual-sex partners would seek a relationship. Women indicated the opposite, wanting a relationship and worrying about becoming too attached to a noncommittal other. Who knew?

Sitting in front of the TV all day can make a teen fat.

Too much television, video games and Internet can increase body fat in teens, according to a five-year study of 744 adolescents published in the American Journal of Epidemiology.

And, yes, the reason could have to do with sitting on your butt more during free time than being active. And, yes, those teens who showed an increase in screen time over the study period had the worst body-fat outcomes.

"Our findings show that youth are at greater risk of increased body fat if screen use increases through high school," said lead author Tracie A. Barnett, a professor at the Université de Montréal's Department of Social and Preventive Medicine and a scientist at the Sainte-Justine Hospital Research Center. "One possible reason is that teens who increase their screen time are simultaneously reducing involvement in, and opportunities for, more active pursuits."

Teens who decreased veg-out time during the study showed the healthiest body-fat profiles.

Novel way to lose weight: Eat less and exercise more.

Shortly after the year started, in early January, Australian researchers announced the only reliable way to lose weight was to eat less, exercise, or do both. But the eye-rolling should be directed toward the magical, fat-burning promises made by some products and eaten up by some consumers.

The researchers intended to disprove the idea that a person can lose weight by simply tricking his or her body into burning calories from fat, not carbohydrates, and thus make stored fat evaporate. Their study showed that mice, genetically altered to burn fats rather than carbohydrates, had body compositions similar to that of normal mice. That's because their bodies simply converted the unused carbs into stored fat.

"Our data urges a correction in people's concept of a magic bullet — something that will miraculously make them thin while they sit on the couch watching television," said Greg Cooney, one of the study researchers and a scientist at Sydney's Garvan Institute for Medical Research.

Caffeine affects kids' sleep.

That stuff we drink in the morning to stay alert seems to do just that. Kids who consume caffeine sleep less, and the more they consume, the less they sleep, a study found. A survey of children's snack and beverage consumption revealed that kids ages 8 to 12 took in the equivalent of nearly three cans of caffeinated soda per day. They also slept an average of 8.47 hours per night, less than is recommended by the Centers for Disease Prevention and Control (CDC).

The survey, conducted by William Warzak, a psychology professor at the University of Nebraska Medical Center, and colleagues, queried parents of 200 children ages 5 to 12. Despite caffeine’s diuretic effect, the kids who drank it didn’t appear prone to bed-wetting.

Kids who study abroad drink more alcohol.

Hey, parents, if you send your kids abroad (to study), a pond away from parental guidance and punishment, they're going to live a little. In October, researchers reported in the journal Psychology of Addictive Behaviors that students doubled how much they drank while they were away, upping their consumption from about four alcoholic drinks per week while at home to about eight weekly drinks abroad.

The findings also support the idea that students younger than 21, the legal drinking age in the United States, take advantage of relaxed drinking laws abroad. The underage students in the study nearly tripled their drinking, whereas students over 21 doubled their intake of alcohol.

Kids raised by gay couples do just fine in school.

So lesbian and gay parents aren't harmful to their kids … really? A study published in August in the journal Demography found that children being raised by same-sex couples have nearly the same educational achievement as children raised by married heterosexual couples.

This finding should be among the most no-duh announcements out there. However, that is not the case, as many remain convinced, against all available evidence, that gay parents are dangerous to children

Stanford sociologist Michael Rosenfeld used the 2000 Census to figure out rates at which children repeated a grade during elementary or middle school. Nearly 7 percent of children raised by heterosexual married couples were held back a year, while about 9.5 percent of children living with same-sex partners repeated a grade.

In fact children of gay and married heterosexual couples were less likely to be held back than their peers raised by opposite-sex unmarried couples and single parents. Another study out this year, this one a review of past research, also suggested kids raised by lesbians do just fine.

You can follow LiveScience Managing Editor Jeanna Bryner on Twitter @jeannabryner.