Superheroes are capable of preposterous feats: They leap tall buildings in a single bound and battle hordes of oversized enemies into the ground. Even if their actions are beyond belief, they typically have a backstory that makes them at least thinly plausible—a scientific explanation for why they can do things no one else can.
Most of us are content to accept these creation stories as they come. Not Stanford biologist and superhero enthusiast Sebastian Alvarado. He has taken the fantastical science underlying superheroes like Captain America and the Incredible Hulk and translated it into real biological terms—and he's found it's not all entirely far-fetched.
Take Captain America. In the comic books, a pipsqueak named Steve Rogers receives injections of "Super-Soldier Serum" and intense doses of "Vita-Rays" and emerges as a strapping, be-masked world-beater. Yeah, right.
Or, why not? The key to Captain America's transformation, Alvarado suggests in a recent Stanford news report, might be epigenetic modification—tinkering with the part of our genomes that controls gene expression. He says we know which genes can increase muscle mass and blood oxygen-carrying capacity—essential modifications if you're to become Captain America—and we have superhero-y tools like "zinc finger nucleases" and "CRISPR/Cas9 systems," which could perform the same role as "Super-Soldier Serum," selectively turning those genes off and on. The Vita-Rays are even easier to explain: Some pharmaceuticals can be activated by ultraviolet light, just like Vita-Rays activate Super-Soldier Serum. Ta-da!
Similarly inventive thinking gets you the Incredible Hulk. In the story, an accident leads physicist Bruce Banner to receive intense exposure to gamma rays. In real life, that kind of event would effectively shatter your DNA, and when your DNA recombined, it could possibly create some novel epigenetic changes. Banner becomes the Hulk when he gets angry, which implies that perhaps hormone surges control his Hulk genes. And his skin turns green because—maybe—of the horrific bruising that would likely happen when your body quickly grew to many times its original size.
Alvarado cautions that even the basic science behind these mechanisms has only been tested in mice and shouldn't be tried at home. Oh come on! It's not like Steve Rogers had any guarantees, and here maybe economics—rather than biology—has something important to say: You almost certainly don't get to be a superhero without taking some risks.