The common refrain, “She must have good genes,” is, for all intents and purposes, an expression of surrender. After all, when it comes to our genetic makeup, the reigning wisdom is that our DNA structure arrives with the stork and there’s not a damn thing we can do about it.Every school kid learns the principles of Darwin’s natural selection theory, which explains that major evolutionary changes occur over millions of years. In other words, when it comes to genes, you’re pretty much stuck with what you get.MORE: Experience, Not Genetics, Shapes Mood But what if we did have control over these complex blueprints, the factors that are seemingly set in stone and yet responsible for our predetermined likelihood of getting certain diseases, how we’ll age, and what exactly we’ll pass on to our children? The ridiculously fascinating science of epigenetics focuses on recently introduced evidence that suggests environmental conditions can affect how our genes express themselves, and even how we can pass new traits along the next generation (read: our kids), instead of waiting a millennia.This news is kind of awesome, yet totally terrifying at the same time. Here’s why.What Does it Mean?Thousands of different genes make us susceptible to chronic diseases like heart disease, obesity, diabetes and cancer. According to epigenetic theory, whether or not these genes are expressed as diseases is determined by how you live your life. You may be susceptible to obesity or heart disease, but if you take the proper lifestyle measures, you may not succumb to them.Several studies have shown that changing lifestyle causes changes in gene expression. Factors like stress, diet, behavior and toxins could activate chemical switches that turn genes on and off and regulate gene expression.Now, we’re not talking complete magic here (though for the record that some scientists contend that epigenetic research is overblown). There’s no question that some sets of traits—our “genetic code”—really are intractable, such as the ones that dictate your hair and eye color. But doctors and researchers believe the majority of them can be considered “epigenetic code,” meaning those that can be coaxed in certain ways.MORE: Change Your Heart Disease Risk with What You Eat  Besides altering your own predisposition for chronic diseases passed down for generations, “epigenetic inheritance” means that the choices we make now can affect our unborn children. Here comes the double-edged sword: If we make lifestyle choices that change our genes for the better, we can pass them on to our children to set them up for a healthier life. But if we make the choice to say, smoke, eat unhealthy foods, or do drugs, our decision becomes not just a physical one, but quite possibly a moral and ethical decision, too.Epigenetics in Action There is compelling evidence to how lifestyle factors can manipulate our genetic expression. A study performed by scientists at the Salk Institute for Biological Studies and published in the journal, Science, found that an organism’s epigenetic code can not only evolve quicker than its genetic code, it can strongly influence biological traits. Although this particular research was performed with plants, the possible implications for humans are interesting. “We found that these plants have an epigenetic code that’s more flexible and influential than we imagined,” said Joseph Ecker, Ph.D., a professor in Salk’s Plant Molecular and Cellular Biology Laboratory, said in a statement. “There is clearly a component of heritability that we don’t fully understand. It’s possible that we humans have a similarly active epigenetic mechanism that controls our biological characteristics and gets passed down to our children.”QUIZ: Do You Have a Healthy Lifestyle? Considering the possibility that our epigenetic code can be quickly altered, taking a proactive stance could mean more than simply making an effort to eat right and avoid risky lifestyle choices. Stress levels can have a significant impact too. Think about it: The body reacts to stressful situations by activating the nervous system and secreting adrenaline and noradrenaline in an evolutionary adaptation commonly referred to as the “fight-or-flight” response. The ill-effects of stress are well-documented, but a recent Duke study published in Nature underscored previous studies that found that chronic stress didn’t just lead to apparent health problems, but it resulted in actual DNA damage. The DNA injury may contribute to problems like the formation of tumors and premature aging. Stress is proven to contribute to gray hair, after all.How You Can Take Control“Basically, epigenetics is proof of what doctors have been saying all along in terms of controlling diet and stress,” says Dr. Frank Lipman, founder and director of the Eleven Eleven Wellness Center in New York City and an expert in the field.He believes we’re moving closer to a future where doctors will incorporate epigenetics into your treatment plans—i.e. if breast cancer runs in your family and you carry the gene, you should eat X-Y-Z to help avoid it—but in the meantime, he advocates sticking to a mainly plant-based diet and avoiding dairy and any meats that aren’t organic, grass-fed or free-range.According to Lipman, the worst offender, especially if you don’t want to stimulate those premature aging genes, may be sugar. “Sugar is the most pro-aging food substance out there,” Lipman says. Beauty-wise, make sure to supplement your diet with fish oil pills (Omega 3 fatty acids), vitamin D3, probiotics and a good multivitamin, he says. And besides getting regular exercise, aim to limit everyday stressors. While you might not be able to control the 97 emails you get per day, you can make it a rule to turn off electronics at night and even on the weekends.MORE: Where to Get Your Omega-3s When it comes to pregnancy, concerned moms-to-be might pick up a copy of our own Dr. Roizen and Dr. Oz’s guide, “You: Having a Baby: The Owner’s Manual to a Happy and Healthy Pregnancy,” which contains a chapter about epigenetics and how closely a woman’s bodily conditions can affect the baby’s health. “A woman’s choices during pregnancy can help determine whether her baby’s genes for a certain condition are turned on or turned off,” said Dr. Oz in a Fit Pregnancy interview. “If a child is exposed to certain stresses in utero—like an inadequate blood supply or the mother’s obesity—the child’s DNA makes predictions about what the world outside will look like based on that exposure. For example, if the mom has high blood sugar during pregnancy, the child’s genes will adjust to expect the same. If she’s malnourished, they will turn on to store more calories, as the child’s DNA is predicting famine; this can lead to obesity in childhood and later.” So basically, pregnant women desperately trying to avoid weight gain? (Come on, we’ve seen you at Lamaze class.) Ironically, you could be setting your child up for weight battles ahead.Finally, don’t forget the impact of “nurture” over “nature.” A new UCLA study examined how learned coping skills can affect our underlying biology, including gene expression. Psychologists were able to identify the oxytocin receptor gene, which they found to be closely linked to depression and psychological resources such as optimism and self-esteem.QUIZ: What’s Your Self-Esteem? More importantly, lead researcher Shelley E. Taylor pointed out that providing a safe, nurturing social environment may trump an innate tendency towards depression. “The benefits that tending provides to children, especially those with genetic risks, are substantial. From life in the womb to the surprisingly resilient brain of old age, the social environment molds and shapes the expression of our genetic heritage until the genetic contribution is sometimes barely evident,” she explained in a statement. “A mother’s tending can completely eliminate the potential effects of a gene; a risk for a disease can fail to materialize with nurturing, and a genetic propensity may lead to one outcome for one person and the opposite for another, based on the tending they received.”The bottom line? You already know to be good to your children, but don’t forget to take care of yourself, too. They’ll thank you for it later.