Their new research found that it is possible to design a mechanism for copying chemical information very accurately without relying on biological enzymes to assemble and separate sequence copies. Instead, the researchers relied only on simple kinds of attachments—molecular binding and unbinding reactions that they designed—and mechanical forces.
Having shown that information can be made to chemically self-replicate, says Schulman, the question becomes, what kinds of messages can be copied in this way?
"Our theoretical work suggests that not just linear sequences but also patterns in two dimensions, similar to wallpaper patterns that repeat every so often, could also be replicated," she says.
The crystals used in the study simply copied information verbatim from layer to layer as they grew, which in itself is insufficient to kick-start a Darwinian evolutionary process. But crystal growth that produces complex patterns resulting in 2- or 3-dimensional structures would, in this context, correspond to a rudimentary "genotype-phenotype" relationship, thereby enriching the Darwinian evolutionary process by introducing complex forms that would be subject to selective pressures, Winfree says.
"Our findings show that there is a bewildering variety of imaginable ways that chemical systems could self-replicate and evolve," he says. "This really puts into question whether or not the way biology does things now is the only possible way that life could be organized on a molecular level."
The PNAS study, "Robust self-replication of combinatorial information via crystal growth and scission," was funded by the Miller Institute of Basic Science, the National Science Foundation, and a National Aeronautics and Space Administration astrobiology grant. Bernard Yurke, a Distinguished Research Fellow at Boise State in Idaho, is also a coauthor of the paper.