  Each living species carries a complex DNA sequence that determines their
unique features and functionalities. It is generally assumed that life started
from a random pool of oligonucleotides sequences, generated by a prebiotic
polymerization of nucleotides. The mechanism that initially facilitated the
emergence of sequences that code for the function of the first species from
such a random pool of sequences remains unknown. It is a central problem of the
origin of life. An interesting option would be a self-selection mechanism by
spontaneous symmetry breaking. Initial concentration fluctuations of specific
sequence motifs would have been amplified and outcompeted less abundant
sequences, enhancing the signal to noise to replicate and select functional
sequences. Here, we demonstrate with experimental and theoretical findings that
templated ligation would provide such a self-selection. In templated ligation,
two adjacent single sequences strands are chemically joined when a third
complementary strand sequence brought them in close proximity. This simple
mechanism was a likely side-product of a prebiotic polymerization chemistry
once the strands reach the length to form double stranded species. As shown
here, the ligation gave rise to a nonlinear replication process by the
cooperative ligation of matching sequences which self-promoted their own
elongation. This led to a cascade of enhanced template binding and faster
ligation reactions. A requirement was the reshuffling of the strands by thermal
cycling, enabled for example by microscale convection. Assuming that templated
ligation was driven by the same chemical mechanism that generated prebiotic
polymerization of oligonucleotides, the mechanism could function as a missing
link between polymerization and the self-stabilized replication, offering a
pathway to the autonomous emergence of Darwinian evolution for the origin of
life.
