Sara Blersch got her hazel eyes from her mom and her sense of humor from her dad. Research suggests she may also have inherited their entrepreneurial tendencies--her parents founded Chainsaws Unlimited, a power-tool retail store, in 1978, and Blersch followed in their footsteps by founding her own floral design and greenhouse retail business, Daffodil Hill Growers, six years ago.

It's no secret that children of entrepreneurs are especially likely to go into business for themselves. But Scott Shane, a professor of entrepreneurship at Case Western Reserve University and author of the new book Born Entrepreneurs, Born Leaders: How Your Genes Affect Your Work Life, says entrepreneurial prowess may have as much to do with nature as nurture.

"If you ask people whether they think there's such a thing as a 'born entrepreneur,' most people say yes," Shane says. "There's a widespread belief that there is some underlying, innate component to entrepreneurship, and we wanted to see if there was some literal truth to it."

Shane and other researchers studied rates of entrepreneurship in hundreds of pairs of identical twins, who share 100 percent of their genes, and fraternal twins, who share 50 percent of their genes. They discovered higher rates of shared entrepreneurial tendencies among the identical twins and determined that roughly 30 to 40 percent of the tendency to be an entrepreneur is innate, not taught.

"We expected there would be a genetic component to entrepreneurship," Shane says. "We were surprised to find that the magnitude of that genetic component was pretty sizable."

That came as no surprise to Dave Brautigan, chief operations officer of Atlanta Refrigeration Service, who describes himself as a "serial entrepreneur." Brautigan remembers helping his grandmother bind books for the small publishing company she owned with his grandfather, and spent weekends and summer vacations making service calls with his dad, who co-founded Atlanta Refrigeration Service in 1969.

So it was no surprise that when he got to college, Brautigan launched a business of his own, Crescent Marketing Service, a marketing company that netted exclusive rights to distribute door-hanger bags to dorm rooms on 13 college campuses. He sold the company after graduation and shifted his focus to his dad's company, expanding it to the U.S. Virgin Islands and taking it from eight employees in 2002 to 109 today.

Brautigan says it's easy to identify the shared traits that make him and his dad successful in business--both are determined, independent extroverts who relish hard work. What's tough is pinpointing whether those characteristics are inherited or learned.

"I want to say it's genetic, because I can remember sitting at a barstool when I was really little and just chatting with whoever was there while my dad made a repair at a restaurant," Brautigan says. "I've never had a problem with public speaking or engaging people in conversation. But I wonder if I was left alone, playing video games, if I would have developed the same trait."

If it's clear that there's some genetic component to the tendency to be an entrepreneur, what's less clear, Shane says, is the exact mix of factors that lead to that tendency. "We're saying that there's a genetic component here, but there are many paths to get the same genetic effect," Shane says.

Inherited genes may lead to certain physiological effects, which could account for personality traits common among entrepreneurs, such as extroversion and openness to new experiences, Shane says. For example, people with low levels of the "feel good" chemical dopamine in their brains are more likely to seek new or novel activities, such as starting a business.

But genetic tendencies are influenced by a variety of environmental factors, and Shane says it's nearly impossible to completely separate nature from nurture.

For example, it's not clear whether a child born with perfect pitch ends up being a professional singer because of his innate musical talent, or because that talent led to voice lessons, artistic scholarships and other opportunities that made the career more likely.

"Even if a person has this innate makeup that makes him or her more likely to be an entrepreneur, genes interact with environmental stimuli," Shane says.

Blersch says this is where it gets tricky for her family, too. She knows she shares her dad's willingness to take calculated risks and his gift of gab, both of which have served them well in business. But she doesn't know whether she was born with these traits or if she learned by watching him.

"My dad is such a people person, and I think that's really important when you're in business for yourself," Blersch says. "We can both see someone's face once and remember their name, and we can talk to them about what they bought last week and how they liked it. But I don't know whether that's a nature thing, a nurture thing or a little bit of both."

Shane says molecular testing is underway to identify genes that may contribute to entrepreneurial prowess. But in the meantime, he says budding entrepreneurs born to a long line of librarians can still find business success. "Environment matters in this equation," Shane says. "Odds are higher that you'll be an entrepreneur if you are genetically predisposed, but that's just odds."

Plus, Brautigan and Blersch both say the lessons they learned from their entrepreneur parents, like work ethic and the ability to think independently, are more important than any innate personality trait.

Still, Brautigan says, his two sons' distinct personalities suggest that there's something to the idea that someone can be a "born entrepreneur." His 2-year-old son is a thinker who's into sports. His 5-year-old son is a natural chatterbox comfortable striking up conversations with anyone who will listen, just like his dad, and a "master negotiator."

"He's the one who will say, 'Hey, the dog got into the garbage. If you give me $3, I'll take it out,'" Brautigan says. "We're like, 'Where did he learn that?'"