Im always trying to understand how this shit works from an evolutionary framework >Brood parasites are organisms that rely on others to raise their young. The strategy appears among birds, insects and fish. The brood parasite manipulates a host, either of **the same** or of another **species**, to raise its young as if it were its own, using brood mimicry, for example by having eggs that resemble the host's (egg mimicry). >Brood parasitism relieves the parasitic parents from the investment of rearing young or building nests for the young, enabling them to spend more time on other activities such as foraging and producing further offspring. Bird parasite species mitigate the risk of egg loss by distributing eggs amongst a number of different hosts.[1] As this behaviour damages the host, it often results in **an evolutionary arms race between parasite and host** as the pair of species coevolve... >There is a question as to why the majority of the hosts of brood parasites care for the nestlings of their parasites. Not only do these brood parasites usually differ significantly in size and appearance, but it is also highly probable that they reduce the reproductive success of their hosts. The "mafia hypothesis" evolved through studies in an attempt to answer this question. This hypothesis revolves around host manipulations induced by behaviors of the brood parasite. **Upon the detection and rejection of a brood parasite's egg, the host's nest is destroyed and nestlings injured or killed**. This threatening response indirectly enhances selective pressures favoring aggressive parasite behavior that may result in positive feedback between mafia-like parasites and compliant host behaviors.[18] Wikipedia: brood parasitism