 The breakthrough technology known as CRISPR-Cas9 is effectively a genetic cut and paste tool, enabling scientists to snip out, insert, and reorder DNA, the basic building blocks of life. Scientists in China have already used the technology to create miniature pigs that are being sold as pets, and a pair of beagles with double the muscle mass, like little Snoopys on steroids. But the bigger promise lies in the potential to combat diseases. Labs around the world are trying to develop CRISPR-based treatments for hemophilia, cystic fibrosis, certain types of cancer, and certain forms of blindness. Other researchers are looking to eliminate infectious illnesses like malaria, Lyme disease, and Zika virus by altering the creatures that spread them. Still other scientists are working to produce pigs that could function as human organ donors, engineer crops that can thrive in the warmer habitats created by climate change, and even revive extinct species like the woolly mammoth, or at least an elephant that really likes the cold. How can one tool potentially do all that? It starts with DNA. DNA stores genetic information in the form of two long strands of smaller molecules, twisted into that familiar double helix. The order of those molecules determines what cells produce, as this genetic code gets translated into amino acids, which produce proteins, which create the cells, muscles, hair, hormones, and bones that make up us. Even small changes to the code can lead to dramatic differences, potentially activating or deactivating certain diseases among much else. CRISPR works by harnessing a defense system in bacteria. Those single-celled organisms are under constant threat from viruses. When they successfully invade, viruses can inject their own strands of DNA in an effort to hijack the cell, converting it into a tiny little virus factory. Bacteria, however, developed a clever trick to combat future invasions. Those that survive the attack copy and store bits of that viral DNA, creating what science writer Carl Zimmer describes as a molecular most wanted gallery. The cell then produces short strands of RNA, one of which carries along that virus' genetic mugshot, within an enzyme that acts like a pair of genetic scissors. If that bit of viral DNA reappears, the RNA latches on, and the enzyme snips it out, disabling the virus. What researchers realized is that they could harness this tool not just to snip out bits of viral DNA, but really any short sequence of DNA they chose. Better still, scientists discovered they could add their own DNA sequence, swapping it in for the bit they snipped out. Researchers have long used earlier genome editing techniques for similar aims, but CRISPR on the whole is proving to be simpler, more reliable, and much cheaper. But the capabilities of CRISPR have also begun to raise concerns as well, because if we can engineer swole dogs, couldn't we also build designer babies, optimized, say, to get into the UFC or the NBA or, say, Harvard? A growing number of scientists and policymakers have called for a moratorium on making changes to human DNA that could be passed along. Altering the human germline for clinical purposes is a line that should not be crossed at this time. At least until safety issues are worked out, and there's a broader consensus that this kind of research should move forward. Meanwhile, the Obama administration has also called for a broader overhaul of the rules covering biotechnology research, in large part driven by the growing power of tools like CRISPR. But it will be no small trick to craft a modern set of rules that can encompass these rapidly advancing technologies, separate valid ethical concerns from knee-jerk genetic engineering reactions, and to ensure safety without sacrificing the very real promise of CRISPR to prevent disease and save lives. I'm just doing one line. I'm just doing the first line. Have, uh, rubber face from Tyson's Chain Sack on it. If I don't get it on the first take. Um. I don't even remember what the f*** I'm saying. You gotta read it. It's coming. It's coming. But the big- But the bigger promise lies. Leather face! You're dead. You're dead. You're dead.