Polypeptide-type dynamic biopolymers (bio-dynamers) have been generated by polycondensation via acylhydrazone and imine formation of amino-acid-derived components that polymerize driven by self-organization. They have been characterized as globular particles, reminiscent of folded proteins, by cryo-TEM, LS, DOSY NMR, and SANS studies. The reversible polymers obtained show remarkably low dispersity and feature double covalent dynamics allowing for fine-tuning of both exchange and incorporation processes through pH control. In the course of build-up, they perform a selection of the most suitable building block, as indicated by the preferential incorporation of the more hydrophobic amino-acid component with increased rate and higher molecular weight of the polymer formed. The system described displays nucleation-elongation behavior driven by hydrophobic effects and represents a model for the operation of adaptation processes in the evolution of complex matter.