When do chemical systems become biological ones? What needs to happen for molecules behaving stochastically to join in networks and cooperate to produce non-random or directed chemical pathways? Biological systems consist of networks of interacting molecules over a large number of time and length scales, and with error tolerance: The larger and more organized the molecules, the more they behave cooperatively. The evolution of biological systems results in interconnected networks optimized for robustness. Such systems are often not the optimal solution, but rather an adjacent one, stable to perturbations. Indeed, before the first genetically regulated ones, such systems had to self-encode into a replicating system. What mechanism led to self-encoding chemistry and was this the seed for biological evolution? This question is perhaps the most important. Finding the first system that is able to evolve is a big challenge.
The first evolving systems started without all the error-correction mechanisms of biology, and chemical reactions do not proceed with 100% yield; they are inherently noisy. Sometimes the reaction produces byproducts, other times, small changes in the conditions lead to changes in products.