In a new interview with NPR, Serena talks about her book, On the Line, which documents her life in tennis, including her on-court relationship with Venus. Serena is close to her older sister, but she says she always felt like the underdog:

Venus was the big star. When we were growing up, it was a lot about Venus—it needed to be about Venus, because she was an incredible player. And that actually, being the little sister, the one that wasn't as strong, wasn't as good yet, gave me encouragement and the fight I have in my game.

While most of us can remember competing against our siblings at some point, being constantly pitted against your sister seems like it could lead to a truly fraught relationship. Not so for the Williams. Serena says she once told Venus that "we'll be sisters later." On the court, they are rivals, but after the game is over they go right back to normal. Serena explains:

In the book I talk about how difficult it was to be there. First of all, I didn't believe I could, and second of all, I was playing my sister. I had to come up with something new, that, right now, we're competitors, but the moment we shake hands and we're done with this match, we're sisters. I'm always happy for Venus, and she's always happy for me.

Serena also talks about an incident early in her career, when she was playing in a tournament at Indian Wells, and her sister was forced to drop out because of an injury. Serena says the angry fans booed and shouted racial epithets. "I was crying in my towel at the changeover. I would cry, and I knew that I had to go on," she recalls. "But I got strength from a lot of the situations like Althea Gibson, who ended up having to sleep in her car because of the color of her skin...And I thought 'wow, this is nothing compared to what they went through,' and I was able to draw strength from that to finish the match."

Serena does mention the recent incident at the U.S. Open, where she threatened a lineman. She offers a weak—but probably honest—explanation for her actions, but she continues to assert that the lineman's call was at fault. When asked "Why do you think that happened?," Serena responds: "A lot of things factored into it... This is a case where I may, not may, I definitely wore my emotions a little too far on my sleeve—on a bad call." She adds, "Just so you know, this is not the first time this happened in tennis, and I definitely think one moment doesn't make your career or define you as a person."

Serena Williams Puts Her Life Story Into 'On The Line' [NPR]

Several studies show small differences among siblings based on birth order. First-borns tend to have slightly higher IQ than second-borns, who score slightly higher than third-borns. First-borns are also slightly taller at the age of 10 than their siblings, meaning they may be better nourished. And parents may have higher expectations for their oldest children: one survey found that 35% of moms thought their oldest would do the best in school,while only 15% thought the youngest would.

Findings like these have led some scientists (including, creepily, eugenicist Francis Galton) to conclude that first-borns are predisposed to run the world. Galton and others have found a high percentage of first-borns in influential political and scientific positions. However, some say younger siblings are the real stars. In his book Born to Rebel, Frank Sulloway uses Darwin and Copernicus as examples of later-borns whose birth order allowed them to take risks and be creative, rather than pleasing parents and other authority figures. The idea that first-borns are high-achieving but law-abiding, while their younger siblings are less conventionally successful but more adventurous, has at this point reached the status of conventional wisdom.

But is it true? Psychology professor Ginger Moore says no. She tells the Times,

There is no doubt that parents treat children differently, and some of that difference may be related to birth order. [...] However, the way that parents interact with their children, the expectations they have of them and the opportunities they give them, most likely have less to do with birth order and more to do with many other factors, such as the child's personality, gender, the number of children in the family, the spacing between siblings and parental age.

The average IQ differences among siblings may be too small to mean much (and IQ test are suspect anyway), and according to Moore, the reason birth order is such a popular explanation for variation among families may be that it's easy to measure. It's also easy to amass anecdotal evidence about. Neil Bush and the famously coked-out Roger Clinton are popular examples of underachieving younger sibs, although to call George W. Bush "more successful" than his brothers is to use an interesting definition of success. But it's just as easy to find examples of later-borns who outshone their siblings. And perhaps most common of all is the family where differences between children transcend birth order.

I'm five years older than my brother, and I remember discovering that most of my friends in college were older or only children. Growing up, I cared a lot about my parents' approval and always did my homework — my brother had to be nagged. I was nerdy while my brother was well-adjusted and popular — supposedly common traits of later-borns. As we get older, however, the picture gets more complicated. I'm probably more of a risk-taker than my brother; he cares more about traditions. He's become more academic than he ever was as a kid; I gave up computer science to pursue creative writing. And some of the closest friends I've made in the last few years have been later-borns. There's pretty much only one way my brother and I currently fulfill birth order stereotypes. We're both at our parents' house right now, and while I'm working, he's sleeping.

Are Eldest Children Really A Cut Above? [TimesOnline]

Psychologists at the University of Ulster and De Monfort University questioned 571 people aged 17 to 25 who had only sisters or brothers, both, or were only children, reports The Daily Mail. Researchers found that subjects who grew up with at least one sister were generally happier, more ambitious, and more emotionally balanced than those who only had brothers. [Aww, I am forwarding this to my sister right now. — Dodai]

"Our explanation for it is that the presence of girls opens up channels of communication and it becomes a much more expressive situation that's positive," said University of Ulster researcher Tony Cassidy, who co-authored the study. "Emotional expression is fundamental to good psychological health and having sisters promotes this in families."

Researchers also found that people with sisters were more successful in their careers, as subjects with sisters were more likely to strive to reach their goals. "It certainly seems there is something about the family situation with the number of girls in it that leads to more encouragement to achieve and be independent," said Cassidy.

Women benefited the most from having sisters in families where the parents were still married, but in divorced families both men and women benefited equally from having sisters. "It seems [sisters'] natural inclination was to express themselves, talk about the separation and encourage other family members to do so as well. It seems to help keep family relationships going," said co-author Liz Wright, research fellow at De Montfort, according to The Times of London. "There was markedly less distress in broken homes with a sister."

Brothers had a less positive effect, and men who grew up with lots of brothers scored the lowest for emotional health. "The more natural trend for boys is not to talk about things," said Cassidy in The Daily Mail. "When there are a number of boys together, it is almost like a conspiracy of silence no to talk, whereas a girl in that context breaks it down."

As for only children, their scores fell between those with only sisters and those with only brothers. "It seems many only children had built up significant social support outside the home by the time they reached their late teens which helped them in a crisis and in other areas of life," said Wright.

Why Having A Sister Makes You Happier And Helps Families Bond [The Daily Mail]
Growing Up With A Sister Makes People More Balanced [The Times Of London]

Now, the order numbers only a hundred nuns, but according to sisters Sisters Virginie Fish and Marcia Hall, a former academic, (interviewed by NPR's Michel Martin) it's still a rich and fulfilling life. The Oblates, who were founded by Mother Mary Lange, a Haitian nun, was an integrated order from inception, and dedicated to good works. Says sister Virginie, who joined the order right out of high school 63 years ago, "We are ordinary women trying to live an extraordinary lifestyle because it it what we feel God is asking of us." Of the order's dwindling numbers she declares, "Jesus had twelve apostles...look what he did with twelve unlikely, uneducated men!" [NPR]

We've discussed sisterhood before; but mostly childhood hijinks and run-of-the-mill adolescent torture. Cyndi Hoffman is 47 years old; Peggy is 33. Are they proof that you're never too old for sibling conflict? What made Cyndi turn in her flesh and blood? Is it because, as author Vikki Stark (My Sister, My Self) said on the Today show this morning (see above clip), older sisters are the "caretakers"? Was Cyndi envious of Peggy? (It was a glowing profile in the Times that prompted Cyndi to phone Peggy's publisher and call bullshit on Peggy's claim that she was a half-white, half-Native American girl who grew up in South-Central Los Angeles as a foster child among gang-bangers and ran drugs for the Bloods.)

Times columnist Tara Parker-Pope points out: "While we choose our friends and rely on our parents, siblings remain in our lives by neither choice nor necessity." As both Parker-Pope and Stark say: The relationship between sisters can powerfully influence the outcome of the womens' lives as adults. If your sister was on her way to becoming a best-selling author in a career built on a lie, would you turn her in? Or is it important to be loyal to your family, no matter what? What do you do when being a good person means being a bad sister?

In Sisters, Love and an Urge to Wring Her Neck, Siblings Behaving Badly, Sibling Battles [New York Times]
In Sisters, Love And An Urge To Wring Her Neck [NBC News]

Earlier: Are First-Borns More Successful Than Younger Siblings?
Older Sisters Are All A Bunch Of Hilarious Sadists
An Open Apology To Our Younger Sisters
Did Faux Memoirist Peggy Seltzer Reveal A Culture Of Narcissism Or Racism?
Female Gang-Banging Memoirist Is More Fiction Than Fact