If you were to boil all of biology down to a simple equation, it would be that DNA makes RNA, which makes proteins, which are what make every living thing you can see, smell, touch, and taste (and a lot of things you can’t). This central dogma of biology, built on strings of Cs, Gs, As, and Ts, has prevailed since Francis Crick, James Watson, and Rosalind Franklin discovered DNA’s double helix 65 years ago. Now that’s changing as scientists expand the code of life beyond the four letters provided by nature.

On Thursday, researchers unveiled the latest feat in artificial DNA engineering: an eight-letter synthetic system called “hachimoji” DNA. From the Japanese hachi for eight and moji for letter, the system is made up of four natural nucleotides and four synthetic ones that all fit seamlessly into DNA’s helical structure, maintaining its natural shape. Moreover, sequences spelled with these new letters pair predictably, and can evolve just like natural DNA. The research appears in the new issue of Science.

Previously, scientists had expanded the genetic alphabet to six letters, but the latest addition doubles the amount of information it’s possible to encode in natural DNA, testing the limits of molecular information storage. That could have immediate impacts on the nascent DNA data storage industry and NASA’s search for life elsewhere in the solar system. It also represents a big step toward the far-off vision of creating alternative life forms—organisms that use a genetic language unlike the one used by every other creature that evolved here on Earth.

“Biology is optimized to do what it wants to do, not what you want to do,” says Steven A. Benner, a synthetic biologist at the Foundation for Applied Molecular Evolution in Gainesville, Florida, who led the work. For decades he’s been trying to create artificial Darwinian systems, to understand if the four chemical letters nature wound up with became the language of life by simple chance. Was it, as Crick famously posited, merely a “frozen accident”?

“This paper, for the first time, definitively answers that question,” says Floyd Romesberg, a synthetic biologist at Scripps Research Institute in La Jolla, California, who was not involved in the work but who has created an artificial genetic language of his own. “For a long time we’ve had hints that life evolved from G, A, T, C, not because they were exactly the right raw materials but because they were simply available. Steve’s four letters [S, P, Z, B] are, at least in terms of stability, in every way equivalent to nature’s four letters.”

So now the question becomes whether broadening that coincidental code could make DNA even better. Having more letters to work with theoretically allows for totally novel molecules that don’t exist in nature—any of which could be useful for making new materials, diagnosing diseases, or developing new medicines. A four-letter alphabet gives you 64 possible codons, which yield 20 amino acids, the building blocks of proteins. Six letters takes you up to 216 codons; eight makes it 512. But that’s mostly meaningless unless someone creates the cellular machinery capable of reading hachimoji and spitting out synthetic proteins with new functions.

In the same way that chemists in the middle half of the 20th century took naturally occurring substances—say penicillin from a petri dish of “mold juice,” or pacliataxel from the bark of the Pacific yew tree—and tinkered with them to make them work better in human bodies, biochemists are eager to do the same with proteins. With more building blocks and new techniques to direct evolution, whose inventors won last year’s Nobel Prize in chemistry, scientists could give proteins advantageous properties that the 20 amino acids in our bodies don’t make available. You can think of those 20 amino acids as mud bricks. They’re good for building two-story houses. But say you want to make a skyscraper? Good luck.