biostudies-literatureUnknown6Zhang HWe study the emergence of conditional cooperation in the presence of both intra-group and inter-group selection. Individuals play public goods games within their groups using conditional strategies, which are represented as piecewise linear response functions. Accordingly, groups engage in conflicts with a certain probability. In contrast to previous studies, we consider continuous contribution levels and a rich set of conditional strategies, allowing for a wide range of possible interactions between strategies. We find that the existence of conditional strategies enables the stabilization of cooperation even under strong intra-group selection. The strategy that eventually dominates in the population has two key properties: (i) It is unexploitable with strong intra-group selection; (ii) ItScientific reports23006https://www.ebi.ac.uk/biostudies/studies/S-EPMC4786827biostudies-literatureEvolution of conditional cooperation under multilevel selection.PMC4786827Zhang HPerc MfalseEvolution of conditional cooperation under multilevel selection.We study the emergence of conditional cooperation in the presence of both intra-group and inter-group selection. Individuals play public goods games within their groups using conditional strategies, which are represented as piecewise linear response functions. Accordingly, groups engage in conflicts with a certain probability. In contrast to previous studies, we consider continuous contribution levels and a rich set of conditional strategies, allowing for a wide range of possible interactions between strategies. We find that the existence of conditional strategies enables the stabilization of cooperation even under strong intra-group selection. The strategy that eventually dominates in the population has two key properties: (i) It is unexploitable with strong intra-group selection; (ii) It2016-01-01T00:00:00Z2016 Mar2025-04-18T22:04:03.805Z2019-03-27T02:10:52ZS-EPMC47868272696564710.1038/srep23006