NEW ORLEANS -- America's leading genetic experts agree: Jim and John Harbaugh have something in common.

"As brothers, half of their genes are identical by descent, plus an additional increment which will be essentially the same," according to Dr. David Valle, Professor of Genetics at Johns Hopkins University.

"Each parent provides half the DNA, but it's not the same half. It gets split differently," adds Dr. Barry Starr, Director of Outreach Activities at the Stanford University Department of Genetics.

Jim and John Harbaugh are brothers, or to use the more scientific and politically correct term, siblings. The Harbaughs held a press conference on Friday to educate the public on their unique biological condition.

Dozens of photographers and hundreds of journalists, plus a national television audience, watched as John Harbaugh took the stage in a dark business suit and a Ravens-colored striped tie, while his younger brother Jim sat beside him in a 49ers sweatshirt and cap, with khaki pants. The Harbaughs look somewhat alike, sound similar and have chosen the same career path, but their differences are also obvious.

Genetics can help explain why. "Geneticists think in terms of phenotypes, clinically observable characteristics of an individual," Dr. Valle explained. Those characteristics can include everything from eye and hair color to the risk factors for diseases, and even some behavioral traits. Environment also plays a huge role in the development of most characteristics, and the fact that siblings usually share similar environmental conditions often adds to their similarities. Still, genetics sometimes play a surprising role in shaping sibling behavior.

Take emotionality. "A chunk of how emotional you are comes from genetics," Dr. Starr said. Studies on infant siblings raised in similar environments reveal that some babies are more easily upset than others. Such a difference may be a factor in the Harbaugh's conflicting personalities. "John is calm and cerebral, while Jim is quite excitable," noted Dr. Starr.

Intelligence is also impacted in part by genetics, with the important caveat that intelligence is a complex phenomenon that includes a spectrum of abilities and behaviors. "The brain is so complicated, and each gene only affects one tiny element of it," Dr. Starr said. "All of these minor tweaks at all different positions can yield so many outcomes."

When two mentally formidable adults produce offspring, the chances that one or the other provided many of the hundreds of genes that affect intelligence is very high, and of course those parents are also likely to provide an intellectually stimulating environment. Still, there are no guarantees. "Two intelligent parents are likely to have intelligent children, but it is possible that it is not so," Dr. Starr explained.

Intelligence and a certain type of emotional makeup are key components to successful coaching. So is competitive drive. Jim Harbaugh said that his mother "competes like a maniac" at the Friday press conference. Could that kind of competitive drive, or some other coaching attributes (organization, self-discipline, the ability to give boring sound bites) also be passed down genetically?

"Geneticists see roles for genes in almost everything," Dr. Valle warned. It's possible that the complex behaviors that yield managerial or motivation prowess have genetic underpinnings, but it is not scientifically testable from a logistics standpoint. "We would need a large grant and a lot of money," he said.

It's safer to assume that Jim and John Harbaugh learned the skills that brought them high-level coaching success, rather than inheriting them. "Discipline and drive speak to the lessons instilled by their parents," Dr. Valle said. As for coaching talent in general, "that set of skills, whatever they are, is truly amazing."

Still, genetic factors paved the Harbaugh brothers' way into the NFL. An individual's height is determined to a degree by environmental factors like nutrition, but genes play an obvious role. Dr. Starr said that a combination of anywhere from 10 to 30 genes influence height, with one particular gene affecting height by a factor of 2 to 3 percent. For young men pursuing athletic careers, taller is typically better. "Jim happened to get more of the tall genes than John. That had a direct effect on their football careers."

While John lacked the size needed to play in the NFL, he was athletic enough to play at University of Miami. Studies of siblings separated at birth reveal that many of the traits associated with athleticism, like cardiovascular capability, are passed down genetically. That athletic ability led to more opportunities for a football career, which of course increased the likelihood that one or the other Harbaugh brother would work his way through the coaching ranks and achieve success at a high level.

In other words, those of us fascinated by the Harbaugh brothers are looking at their story in exactly the wrong way. The odds of two brothers facing each other as Super Bowl coaches are not astronomically low. In purely mathematical terms, they are actually pretty good, at least as compared to any two random strangers.

The scientists agree. "The relative risk of them being successful coaches is much higher than two people picked from the general population," Dr. Valle said, relative risk being a genetic term for any outcome, not an indictment of the perils of coaching in the NFL. "From genetics and the environment, they have better odds than most people," added Dr Starr. "They have the tools and the right situation to get where they are now."

The Harbaugh brothers made the best of their strange spectacle of a press conference, trading quips and knowing glances, sharing the few family tales that have not been shared dozens of times since Jim first joined John in the NFL coaching ranks in 2011. (Their first joint press conference technically took place during the 2011 Scouting Combine, when Jim showed up while John was speaking.) The brothers took the Super Bowl hype in stride and provided a touching moment when they invited their parents and grandfather onto the stage, 97-year old grandpa Joe wearing a half-and-half 49ers-Ravens hat. The Harbaugh family has managed to provide warmth to an event that sometimes descends into noisy spectacle.

Still, there is something strange about our fascination. Brothers who are so similar yet so different, who both excelled at their father's chosen career but chose to go about things a different way: Who could imagine such a thing, except a genetic researcher, or perhaps any parent who has had two children, dating back to Adam and Eve?

One thing genetics cannot tell us is who will win. Our experts were carefully chosen from the San Francisco and Baltimore areas, eliminating bias and ensuring repeatability of results, two major tenets of scientific practice. Dr. Valle is an avowed Ravens fan, which is why he offered this opinion from the field of developmental psychology, which is far beyond his professional expertise. "I'm a Ravens fan, so I think the older sibling is wiser and more likely to be successful."

Dr. Starr and Jim Harbaugh shared an employer for a few years, but that does not mean his loyalties are firmly established. "I'm rooting for the 49ers," he said, "But I'm torn, because I really like Ray Lewis.