If they traveled slowly, they would die, if fast, they would catch fire. Freeman J. Dyson, a mathematical physicist better known as one of the architects of quantum electrodynamics, took a mid-career detour into theoretical biology that resulted in a thin volume titled Origins of Life . The essence of my father's hypothesis was that life began not once, but twice.
Cells can reproduce but only molecules can replicate.
In modern times, reproduction of cells is always accompanied by replication of molecules, but this need not always have been so. The most striking fact which we have learned about life as it now exists is the ubiquity of dual structure, the division of every organism into hardware and software components, into protein and nucleic acid. I consider dual structure to be prima facie evidence of dual origin. Once metabolism is infected by replication, as the Darwins showed us, natural selection will do the rest. If organisms truly replicated, or reproduced even an approximate likeness of themselves without following a distinct set of inherited instructions, we would have Lamarckian evolution, with acquired characteristics transmitted to the offspring.