The Earth-Moon-Sun system... what a joy to behold! It's a little hard to understand at first, but these interactive flash simulations make it a whole lot easier. Say thanks to McGraw-Hill.
"Thank McGraw-Hill"
That's nice, children. :-)
Lunar Phases
Earth Seasons
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Identical twins form when a fertilized embryo splits into two embryos early in development. These twins get the same genes from their parents, but such siblings aren't the same people.
Identical twins form when a fertilized embryo splits into two embryos early in development. These twins get the same genes from their parents, but such siblings aren't the same people.
nojustice/iStockphoto
I have a friend who looks just like me. We both have light brown hair that we wear pulled back, often in pigtails. We dress in the same types of sporty clothes. Our glasses have thick rims and a blue tint. We are both journalists, athletes and moms to little kids. Even our husbands look alike, and even they get my friend and me mixed up sometimes. Everywhere we go, strangers ask us if we’re twins.
My friend and I are not even related. But it’s fun to feel like I’m looking in a mirror when I look at her. And the attention we get helps me imagine what life must be like for actual twins.
Being a “pretend twin” is also fun for me because I’ve always wondered what it would be like to have a sibling who seemed just like me, but was actually a different person altogether. And I’m not the only one who is fascinated by these rare pairs. Lots of scientists are, too.
“It’s a unique birth situation,” says Nancy Segal, a psychologist and twin researcher at California State University, Fullerton. She’s the author of two books about twins and a twin herself. “You feel a little bit special.”
Twins offer scientists the perfect opportunity to study what makes people who they are, Segal says. That’s because twins share more in common than ordinary siblings. Yet, twins still end up being different from each other in important ways — both physically and socially.
By probing these similarities and differences, scientists can begin to figure out which qualities we are born with and which ones result from our experiences. In science, these questions lie at the center of a classic debate called “nature vs. nurture.”
“People study twins not because they’re interested in generalizing about twins,” says Matthew McGue, a psychologist at the University of Minnesota, Twin Cities. (The neighboring Minnesota cities of St. Paul and Minneapolis are called the Twin Cities.) Rather, he says, scientists study these people pairs to learn about the human condition.
I think twins are really cool. there's not much to opionate about but i would like to say that being a twin would be awesome. my moms and twin and her and her sister laugh the same. it's really cool!
-Abbie
WOW!!!! THAT WAS A MOUTHFUL!! =]
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