Increasing new levels of knowledge on living beings and their constitution lead to a general reassessment of constraints notion. The binding action among different causal processes in and out organisms seems to have heuristic value as it lay down paths of future evolution, but not the determination of linear effects. Particularly, the study of long lasting relationships networks and mutual memberships between organisms and their different species of bacteria-host contribute to elucidate such binding-action over time, implying a sort of cultural and environmental assimilation inside the organism. This approach requires a philosophical reflection on crucial concepts such as «individual», «environment», «species», and consequently a critical investigation on ubique references about health and disease. Biological history of cohabitation and cooperation between hosts and symbionts among species suggest two major implications, we aim to explore: a) the individual co-selection performs himself as a sort of ecosystem and it theoretically cracks the principle of determinism, which usually distinguishes naturalism; b) the focus on evolutionary theory shifts from becoming process to structural constraints that marked evolutionary irreversible thresholds (as remote coexistences bacterial insertion even in the human genome).