Different parts of the genome are transmitted in different ways, and therefore may have conflicting reproductive interests. For example, mitochondria are transmitted mostly from mother to daughter, whereas autosomes are passed equally to both sons and daughters. Mitochondria and other matrilineal elements therefore favor a female-biased sex ratio, whereas autosomes tend to favor an equal sex ratio. Conflicting modes of genetic transmission cause many interesting traits, such as cytoplasmic male sterility in plants, sex ratio biasing bacterial and viral symbionts, and high frequencies of transposable genetic elements. Many aspects of genomic organization and patterns of genetic variation can only be understood in the context of genomic conflict.
Populations often contain high levels of genetic polymorphism for resistance to pathogens.
The effectiveness of this resistance is limited because the pathogens are, in turn, widely polymorphic for host-range genes that can escape host resistance. I have also studied the evolution of mutual harm or benefit in symbiosis . But the costs of virulence may be offset by increased competitive success against other parasites within the host or by greater transmission to other hosts. The different replicators have a shared interest in using the body's resources prudently, but also conflict over the distribution of resources. This general view of symbiosis applies to the evolution of protocells and genetic systems near the origin of life, to genomic conflict, to the evolution of ecological mutualisms, and to the evolution of group living and social behavior .