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Having A Sister Might Make You Less Competitive

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Your siblings shape your development in all sorts of ways. You play with them, fight with them, learn from them, and probably ask them inane questions your parents are too tired to answer. They’re often the peers you spend the most time with growing up, and being the oldest or the youngest certainly plays a role in finding your place in the family dynamic. Your birth order and your sibling’s gender might also influence your personality. 

For men, having an older sister can decrease the likelihood of being a competitive person, according to a recent study in the journal Personality and Individual Differences by Okayama University economist Hiroko Okudaira. Compared to men who were only children, men who had older sisters (but no older brothers) weren’t as interested in competing for prizes and money in a series of tasks across two studies of Japanese students.

In the first study, 135 Japanese high school students solved mazes in exchange for points that could be traded for prizes. Before the task, they had to select whether they would rather get points according to the number of mazes they solved, or be entered into a tournament against other participants, in which you had to solve more mazes than the rest of the group to get points (a competitive environment). Only 38 percent of men who had an older sister entered the tournament, showing a lower preference for competition than men with no older sisters.

In a follow-up study, 232 university students solved math problems for cash, with the same tournament setup. Only 24 percent of men who had older sisters entered the tournament, compared to 48 percent of the rest of the men. 

The second study is limited by the fact that it studied only university students at Osaka University, a very selective college, thus increasing the likelihood that the participants would already have a preference for competition. However, psychologists have long speculated that having siblings of the opposite sex can affect the gender-stereotypical traits you exhibit, and this provides further evidence for that claim. 

Why would having a sister influence your personality? Having an older sibling of the opposite sex has been shown to decrease the stereotypical gender roles you inhabit. Competitiveness is a stereotypically male trait, influenced by testosterone, so having an older sister may mediate that characteristic in boys. However, women with older brothers were not significantly more competitive in either of the tests. Here, birth order may also play a role, as later-born kids are generally less dominant than their first-born siblings.

Sorry guys, but it seems like your bossy older sis will still be controlling you long after you outgrow childhood spats.

[h/t: BPS Research Digest]

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Math Symbols Might Look Complicated, But They Were Invented to Make Life Easier
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Numbers can be intimidating, especially for those of us who never quite mastered multiplication or tackled high-school trig. But the squiggly, straight, and angular symbols used in math have surprisingly basic origins.

For example, Robert Recorde, the 16th century Welsh mathematician who invented the “equal” sign, simply grew tired of constantly writing out the words “equal to.” To save time (and perhaps ease his writers’ cramp), he drew two parallel horizontal line segments, which he considered to be a pictorial representation of equality. Meanwhile, plenty of other symbols used in math are just Greek or Latin letters (instead of being some kind of secret code designed to torture students).

These symbols—and more—were all invented or adopted by academics who wanted to avoid redundancy or take a shortcut while tackling a math problem. Learn more about their history by watching TED-Ed’s video below.

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The Homemaker Who Helped Solve One of Geometry's Oldest Puzzles
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V via Flickr // CC BY-NC 2.0

The next time you find yourself staring at your bathroom floor tiles, thank Marjorie Rice. The San Diego homemaker helped solve one of the oldest problems in geometry: figuring out which shapes could "tile the plane," or seamlessly cover a flat surface in an endless, repeating pattern. Rice's hand-drawn doodles in the 1970s led to major discoveries in the last few years, finally answering the puzzle that had stumped classical thinkers.

Ancient Greek mathematicians believed that certain shapes could tile the plane, without overlapping or leaving any gaps, in a pattern called a tessellation. They proved that all triangles and quadrilaterals, and some convex hexagons (six-sided shapes), could tile the plane. But for centuries, no one knew how many tiling convex pentagons (irregular five-sided shapes) were out there.

The hunt for tiling pentagons began in 1918 when German mathematician Karl Reinhardt described the first five types of tessellating pentagons. For 50 years it was believed that he had found them all, but in 1968, physicist R. B. Kershner discovered three more classes. Richard James, a computer scientist in California, found another in 1975, bringing the total to nine.

That year, Rice read a column by Martin Gardner in Scientific American about the research and began experimenting to find more tiling pentagons. "I became fascinated with the subject and wanted to understand what made each type unique," Rice wrote in an essay about M.C. Escher's use of repeating patterns. "Lacking a mathematical background, I developed my own notation system and in a few months discovered a new type which I sent to Martin Gardner. He sent it to Doris Schattschneider to determine if it truly was a new type, and indeed it was."

Schattschneider, a mathematics professor at Moravian College in Bethlehem, Pennsylvania, deciphered Rice's notation and realized she had found four new types—more than anyone other than Reinhardt. Schattschneider helped formally announce Rice's discoveries in 1977.

"My dad had no idea what my mom was doing and discovering," her daughter Kathy Rice told Quanta Magazine.

It took another eight years for the next type of tiling pentagon to be found, this time by University of Dortmund mathematician Rolf Stein. Then the trail went cold for 30 years.

In 2015, mathematicians Jennifer McLoud-Mann, Casey Mann, and David von Derau at the University of Washington, Bothell, found the 15th class of tessellating pentagon using a supercomputer. Then, in July 2017, French mathematician Michaël Rao completed the classification of all convex polygons, including pentagons, that can tile the plane. He confirmed that only the 15 known convex pentagons could tessellate [PDF].

The immense amount of research and the scale of the recent discoveries makes the achievements of Marjorie Rice all the more impressive. Though she lacked more than a high-school education and access to supercomputers, Rice remains the most prolific discoverer of tiling pentagons to emerge in the century since Reinhardt first attempted to crack the problem.

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