Ravens Coach John Harbaugh, above, and his brother Jim, the 49ers’ head coach, will face each other for the first time Thanksgiving night. (Nick Wass/AP)

John Harbaugh was born in 1962 and Jim Harbaugh was born in 1963. The two brothers shared a bedroom for 18 years, and this week on Thanksgiving Day they will share a football field for three hours.

The first pair of brothers to be head coaches in the NFL will meet for the first time.

John is in his fourth year coaching the Baltimore Ravens and Jim is in his first season with the San Francisco 49ers. To further hype the 49ers-at-Ravens game Thursday, it might help if the brothers really, really, really, really, really, really, really didn’t like each other, like King John I and Richard the Lionheart.

Alas, apparently they are rather close and do like each other.

The Harbaughs are part of a growing tradition of U.S. sporting family dynasties.

Just in the last generation, there have been two sublime sibling combos: In tennis, Venus and Serena Williams; in football, Peyton and Eli Manning. Of course, sports and entertainment often produce prodigious family connections. Here is an abbreviated list of significant sibling combos among athletes and actors:

Best Baseball Trio (1930s-1950s): Joe, Vince and Dom DiMaggio.

Best Baseball Trio (1960s-1970s): Matty, Jesus and Felipe Alou.

Best Baseball Trio (1990s-2000s): Yadier, Bengie and Jose Molina.

Best Boxing Brothers: Wladimir and Vitali Klitschko.

Best Boxing Brothers With Fewer Teeth: Leon and Michael Spinks.

Brother-Sister Card Sharks: Howard Lederer and Annie Duke.

From Jocks to Ex-Jock Broadcasters: Cheryl and Reggie Miller, John and Patrick McEnroe, Sterling and Shannon Sharpe.

Richest Twins: Mary-Kate and Ashley Olsen.

Richest Twins (NFL): Ronde and Tiki Barber.

Why? Why? Why?: Paris and Nicky Hilton.

Yes, They Are Brothers: Albert Brooks and Super Dave Osborne.

You Can’t Overlook the Baldwin Boys: Alec, Stephen, William and Daniel.

Where Did All These Arquettes Come From?: Rosanna, Patricia, David, Alexis and Richmond.

There Are More Wayans in Hollywood Than There Are Wangs in Hong Kong: I do not have room to list all of them here.

Best Fictional Sibling Rivalry: Frasier and Niles Crane.

In terms of bitter sibling rivalries at the highest level of their professions, perhaps none in the last century equals that of two sets of sisters:

Olivia de Havilland and Joan Fontaine.

Ann Landers and Abigail van Buren.

Between them, de Havilland and Fontaine garnered seven Academy Award nominations for best actress. But they had an uneasy relationship as adolescents and an estranged relationship as Hollywood leading ladies.

In fact, de Havilland, 95, and Fontaine, 94, reportedly have not spoken since 1975.

(Personal disclosure: I haven’t talked to my brother Steve in nearly three months, but that’s because he’s too busy and I’m too lazy.)

As for the Ann Landers-Dear Abby feud, first let me ask discerning readers this:

What are the chances that two sisters simultaneously would write newspaper advice columns? To me, it’s a statistical improbability — I’d find it more plausible if two siblings discovered plutonium and won “American Idol” in the same lifetime.

Anyway, Eppie Lederer began writing Ann Landers in 1955, and her twin sister Pauline Phillips started writing Dear Abby several months later. By 1958, they were no longer speaking to each other — frankly, they could’ve used some advice — and it was a fractious bond until Eppie passed away in 2002.

Meanwhile, in Elmore, Ohio, this year, it was brother vs. brother for mayor. Incumbent Lowell Krumnow beat his older sibling, councilman Jim Krumnow, 384-245, in the recent election. This was a case of two brothers who just don’t like each other — to avoid political discussions, Jim didn’t even go to the last two Christmas parties at Lowell’s home.

That won’t be the case with John and Jim Harbaugh. On Friday after Thanksgiving, they’ll be together to celebrate their parents’ 50th wedding anniversary. They’ll eat turkey a day late and, perhaps, watch some game film.

Ask The Slouch

Q. So Bud Selig might add another playoff team in each league. How long until they simply do away with the wild card in favor of a Major League Baseball Postseason Security Council, a la the United Nations, with the Yankees and Red Sox named permanent members? (Ian Squires; Washington)

A. You sound smart enough to be MLB’s new secretary-general.

Q. Did you ever get married because there wasn’t anything to watch on TV except soccer? (Bud Huston; Willoughby, Ohio)

A. October 1984. But that was before truTV.

Q. Since the NBA season probably won’t happen, shouldn’t we let the kids who left college early for the draft go back to school so they can resume getting paid? (Rob Mueller; Brookfield, Wis.)

A. Pay the man, Shirley.

You, too, can enter the $1.25 Ask The Slouch Cash Giveaway. Just e-mail asktheslouch@aol.com and, if your question is used, you win $1.25 in cash!