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Conflicts are reduced by changing who benefits from cooperation, constraining opportunities for selfish success, or imposing costs on exploiters. The same logic operates between organisms and inside them, but the units that reproduce and transmit differ. Resolution need not mean eliminating all conflict or giving every participant its preferred outcome: it can be a stable compromise, suppression by a powerful party, or a continuing arms race.

An evolutionary conflict exists when different inherited strategies or replicating lineages favour different outcomes. Between organisms, individuals may disagree over resources, mating or contributions to a shared activity. Within an organism, cell lineages can gain from proliferating at their neighbours' expense, and genes can gain a transmission advantage that harms the rest of the genome. A common environment or membership of one body does not guarantee identical interests.

Between organisms, alignment can make restraint individually worthwhile. Genetic relatedness can reward benefits to relatives through inclusive fitness; repeated interaction can link current help to later returns; and partner choice can make productive cooperation a condition of continued association. Reliable exchange can also make a partner's survival directly valuable. None of these mechanisms requires conscious agreement. They work only where their gains outweigh the available selfish alternative, including the costs of assessment and enforcement.

Conditional allocation supplies another route. In soybean experiments, preventing rhizobial nitrogen fixation reduced bacterial reproductive success, while physiological measurements implicated reduced oxygen supply to non-fixing nodules. This supports host control that makes poor service costly to the symbiont. The treatment forced noncooperation in an otherwise cooperative strain: it tests the consequences of service failure, rather than demonstrating the evolutionary origin of a particular cheating mutation.^[ref]

Social insects show how relatedness and enforcement interact without making a colony conflict free. Workers can produce haploid sons, creating disagreement over male production. With a sufficiently multiply mated queen, a worker may be more related to queen-produced males than to the average other worker's sons. Experiments in honeybees found strong discrimination against worker-laid male eggs, supporting worker policing. The result establishes differential treatment of eggs; relatedness and colony productivity are possible selective benefits and must be evaluated rather than assumed equivalent.^[ref]

Within multicellular organisms, common descent changes the baseline. Development from a single-cell bottleneck normally makes most cells close genetic relatives and links their lineage's long-term transmission to successful reproduction of the organism. Germline-soma differentiation further restricts the routes by which a proliferating somatic lineage can reach future generations. These features help explain extensive cellular cooperation, but they are incomplete protection: somatic mutation can create a clone that grows faster within the body even while lowering host survival or reproduction.

Cell-cycle regulation, DNA-damage responses, apoptosis, tissue architecture and immune responses can restrict such expansion. Some mechanisms remove damaged cells; others reduce opportunities for spread or prevent extra divisions from translating into transmission. Their developmental and maintenance functions mean that they should not all be described as adaptations exclusively for cancer suppression. Cancer demonstrates that the constraints can fail, especially when selection on the organism is weak at ages after most reproduction.

Apoptosis and cell competition are also not automatically measures of collective welfare. In experimental Drosophila tissues, higher Myc expression made clones eliminate lower-Myc neighbours and expand at their expense. This showed that a process involving elimination of neighbouring cells can be exploited by a locally successful lineage. It cautions against labelling whichever cells win a contest “best for the organism.”^[ref]

Genetic conflict can persist even when cells descend from one zygote, because loci may have different transmission rules. A sex-linked meiotic driver can increase its own representation by impairing gametes carrying the alternative chromosome. Autosomal alleles can instead favour restoration of a more balanced transmission system. In Drosophila simulans, genetic and molecular work identified the autosomal suppressor not much yang, which suppresses an X-linked sex-ratio distorter; cytological work connected distortion to failure of Y-bearing sperm maturation. This is a concrete case of a genomic countermeasure, rather than an assumption that Mendelian inheritance is intrinsically immune to selfish elements.^[ref]

The comparison reveals two common principles. First, common transmission can align interests, as in relatives, vertically transmitted symbionts and clonally developing cells. Second, discrimination can make selfish strategies less profitable, as in partner sanctions, worker egg removal and suppression of a driver. Compartmentalization can help target the responsible partner or lineage, but its effect depends on scale: a compartment founded by one symbiont may reduce within-compartment mixing while still allowing competition among host compartments.

There are also important differences. Separate organisms can often leave, switch partners or use outside resources, so the costs of exit shape bargaining and partner choice. An ordinary somatic cell has few such reproductive alternatives and is usually integrated into a developmentally specified body. Genes inside that cell cannot choose partners in the behavioural sense, but recombination, linkage and differential transmission change the selection acting on suppressors. At either scale, suppression can select for evasion, producing continuing counteradaptation rather than permanent harmony.

A successful explanation therefore specifies the competing units, their routes of transmission, the benefit of the proposed control mechanism, and the level at which success is measured. More offspring, more surviving symbionts, a larger clone and greater representation of one chromosome are different outcomes. Conflicts are resolved to the extent that mechanisms make the lower-level selfish alternative less successful relative to its competitors; neither organismal organization nor social cooperation is evidence that the underlying conflict has vanished.