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If you want your kid to be an elite athlete, make sure they have older brothers or sisters. That's one of the insights in a new book, The Best: How Elite Athletes Are Made, which digs into the social science of athletic greatness.

The book is a collaboration between sports scientist Mark Williams and sports writer Tim Wigmore. We recently spoke with Wigmore to figure out how we can finally become champion basketball players. Turns out, it's too late for us. But maybe not for your kids. At least, the youngest ones.

"Study after study shows that younger siblings have a much greater chance of becoming an elite athlete than older siblings or only children," Wigmore says.

As kids, little brothers and sisters are usually smaller and weaker than their older siblings, which means they have to work harder to keep up. This forces them to develop skills and tenacity. Michael Jordan had Larry Jordan, his 11-month-older brother, whom he credited in The Last Dance for motivating him to be a better player. Tennis goddess Serena Williams had Venus Williams, also a pro tennis player.

But what about Peyton and Eli Manning?! Everyone knows Peyton, the older brother, is the better quarterback. Not so fast, Wigmore says. Peyton, too, had an older brother, Cooper, who also played football.

Wigmore says another factor that helps younger siblings is more lackadaisical parenting. The research, he says, suggests parents are usually more hands off with their younger ones, giving them more time to informally play — like, for example, pickup basketball — which helps them develop their athletic skills through trial and error. That, he says, can be more valuable than rigid, top-down instruction. Think freewheeling, chicken-chasing Rocky Balboa defeating Soviet bureaucracy-trained Ivan Drago. (Rocky IV is the best Rocky, by the way.)

For what it's worth, Wigmore is an only child. "And that helps to explain why I write about sports rather than play them," he says.

Location matters

Another ingredient that helps create elite athletes: growing up in a midsize town.

"If you grow up in a town of between 50,000 and 100,000, you're 15 times — 15 times — more likely to become an elite athlete than if you grew up in an area smaller or bigger," Wigmore says. Michael Jordan grew up in Wilmington, N.C., which fit the bill during his childhood (these days it's slightly over 100,000 people). During the 20th century, Wilmington produced a huge number of elite athletes, including Sonny Jurgensen, a NFL quarterback Hall of Famer, and Sugar Ray Leonard, an Olympic gold medalist in boxing.

Wigmore says research finds the midsize-city phenomenon all over the world. "Midsized towns have the perfect combination of rural and urban living," he says. "You get the space that you get in rural areas, but you also get the kind of quality of competition and coaching that you get in urban areas."

Midsize towns also fall in the sweet spot when it comes to supply and demand for athletes. They're big enough to have a diverse array of people to recruit from, but they're also small enough that players will be in demand. Coaches may encourage more kids to play — even if they're not good yet — and help them reach their potential. "There's been studies of dropout rates, and they find that if you're in cities with over half a million people, kids are about three times more likely to drop out of a certain sport than kids in these midsized towns," Wigmore says.

When you're born

Jordan had another thing going for him: He wasn't born in July. That, according to Williams and Wigmore, is the worst month to be born in if you want to be an elite athlete. The reason is simple: It usually means you'll be young for your school year, which typically cuts off around then. Being younger than your peers in adolescence can mean fewer inches in height and fewer pounds of muscle, which has obvious effects in various sports. It's known as the relative age effect, and it affects academic achievement as well. Malcolm Gladwell wrote about it in his 2008 book, Outliers.

But interestingly, Wigmore says, there's a small number of athletes for whom being born in July (or whenever the cutoff month is for a school grade) is actually an advantage. Kids born late for their school year have a lower chance of becoming professional athletes — but a higher chance of becoming "super-elites" and winning MVP awards if they do. It's called the underdog effect. It's when the younger kids have to work harder — as if they are a younger sibling — to compete with the older kids. And for some kids, when they do get their growth spurt, they then have the skills, tenacity and, finally, the physical prowess to be a top athlete. It's a bit like being awkward looking as a kid and being forced to develop your personality, and then one day you get over your awkward stage and become the perfect package.

So if you're a parent or thinking of becoming one, move to a town with between 50,000 and 100,000 people, like Dearborn, Mich., or Yakima, Wash. Have multiple kids. Make sure they're old for their grade or have the tenacity to keep up with older kids until they get their growth spurt. And then maybe you can be one of those people crying in the stands, screaming, "That's my girl!"

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