ATLANTA — Not since Sister Sledge hit the charts with ”We Are Family” (1979) has siblinghood been celebrated quite so loudly as today. The bonds of blood have become big headlines — and figure to stay that way at least until one Harbaugh falls.

We have brothers in conflict: The Super Bowl pitting San Francisco’s coach Jim Harbaugh against Baltimore’s John. Or is that the other way around? Anyway, by the time the hype mill is done machining that story line, Cain vs. Abel will look like “Leave it to Beaver” by comparison.

And now, we have brothers together in the outfield: We’re officially up to our armpits in Uptons, the Atlanta Braves trading for Justin to join free-agent acquisition B.J. The Braves are banking much on the power of brotherly glove.

A French writer once declared that, “A brother is a friend given by Nature.”

Justin Upton, the younger and more outgoing of the two, put the sibling relationship bluntly: “I wouldn’t be the player I am if (B.J.) cut me any slack,” he said to USA Today a few years back.

The Uptons tell a story that is oh-so common among sporting brothers and sisters, one that helps explain why there are so many examples of family ties in athletics. There are benefits to growing up together in a sports-centric household, feeding off each other’s competitive instincts, transforming the natural sibling rivalry into training for bigger games to come.

Because of the three years separating them, the Uptons played little organized ball together: One year on a fall travel team, the Tidewater (Va.) Mets, when Justin was a high school freshman and B.J. a senior.

Their competition consisted of childhood games in the front yard, when B.J. hit tennis balls pitched by Justin over neighbors’ roofs. Then they’d flip it around, and older brother would routinely strike out the younger. Often, to keep Justin on his toes, B.J. would drill him with a high, hard Wilson. Because that’s what big brothers do.

There is an expectation that joining the two at Turner Field will spark all kinds of beneficial interaction. They are well past the stage of Justin getting upset with his brother and running inside crying.

“I think there’s no question, talking to both of them, how much admiration they have for each other and how much they’ve looked forward and dreamed of this opportunity to play together,” Braves general manager Frank Wren said. “I do think it will drive them, I think it will push them.”

Anticipating the joy of going to work every day with his brother, Justin sees the arrangement as a significant emotional tailwind. “The more energy you can bring to the yard every day makes you a better player,” he said last week.

Forty years ago, Joe Niekro joined his older brother Phil in Atlanta for a couple of years — the two also played briefly together for the Yankees in 1985. Hall of Famer Phil counts those three seasons with his brother among the best of his 24-year career.

“You’re spending a lot of time with each other doing what you love to do — playing baseball. It doesn’t get much better than that,” he said.

When reunited in Atlanta, Phil was able to reintroduce his brother to the family tradition — the knuckleball. They won 539 games between them, the most by any brother combination in baseball (the Perrys, Gaylord and Jim, had 10 fewer).

And for that brief slice of time they played together, “When you saw me, you saw Joe; and when you saw Joe, you saw me. We were inseparable, like twins almost,” Phil said. Joe died in 2006.

Another Hall of Fame Brave, Henry Aaron, can speak to the B-side of playing with your brother, when one is galactically more gifted.

No brother combination has more career home runs than the Aarons. Henry had 755. Tommie had 13.

Try to imagine how difficult it was to be the baseball-playing brother of the great Henry Aaron, and then to be paired with and compared with him on a regular basis (as he was in Milwaukee and Atlanta for parts of seven seasons between up to 1971).

“He was having some tough times playing here (in Atlanta),” Henry said of his brother, who died in 1984 at the age of 45.

“He was a terrific ballplayer. I had been in the big leagues a long time, and I’m sure everything I had done, people were thinking he would do. It hurt him in a way. I think if he had the opportunity to play on another club, he would have done much better.”

As least the Uptons are a more equally matched set.