The synthetic theory of evolution is the fusion of Mendelian genetics and Darwinian evolution. It began with the establishment of theoretical population genetics in the first third of the twentieth century showing how natural selection and other evolutionary processes affect the frequencies of Mendelian alleles. During the middle third of that century, various disciplines of biology – genetics, systematics, paleontology – were folded into the synthetic theory. The synthetic theory assumed that evolutionary changes over long stretches of time were the accumulation of small changes within species. This entry concludes with a discussion of the various challenges that have been made to the synthetic theory since the 1960s.

Because they cannot easily flee from natural enemies, plants are particularly prone to threats from other organisms including pathogens and animal herbivores. Moreover, plants often face intense competition for resources (including space) from other plants. When referring to agricultural plants and other plants of human concern, these pathogens, herbivores, and other competing plants (weeds) are collectively known as pests. Pest management encompasses human activities that limit the damage from pests to preferred plants. Managing pests is particularly critical to agriculture as losses from pests can cause substantial loss of crops, especially in areas of food insecurity and fast-growing human populations. Because of space limitations, this entry focuses on the management of insect and microbial pests that threaten agricultural plants; however, similar principles apply to forest pests and urban pests as well as to weeds. Pest management is an applied science that relies heavily on concepts, principles, and information from ecology, genetics, and evolutionary biology. Evolutionary principles help identify current pests and help biologist predict which organisms are likely to become pests. Evolutionary biology also influences pest management strategies. Chemical agents (pesticides) can be effective in managing or even eliminating pests, at least for a while, but nfortunately, pests can evolve resistance to those pesticides. Understanding how pests evolve resistance can help in the development of practices aimed at slowing the evolution of resistance. Guidance from evolutionary biology also assists in the best use of a plant’s natural defenses and use of biological control agents in pest management. Pest management benefits from information about the genetic basis of traits of the host plant and or their pests. For instance, knowing that a gene affects an insect pest’s resistance to a specific pesticide can help to thwart the evolution of resistance in that insect or to develop new insecticides. In recent years, DNA markers have increasingly been used to find genes that likely contribute to specific phenotypes of interest and regions of the genome that have been impacted by selection. Development of these tools rest on a foundation of evolutionary genetics.

Biological resistance to pesticides, vaccines, antibiotics, and chemotherapies creates huge costs to society, including extensive morbidity and mortality. We simultaneously face costly resistance to social changes, such as those required to resolve human-wildlife conflicts and conserve biodiversity and the biosphere. Viewing resistance as a force that impedes change from one state to another, we suggest that an analysis of biological resistance can provide unique and potentially testable insights into understanding resistance to social changes. We review key insights from managing biological resistance and develop a framework that identifies seven strategies to overcome resistance. We apply this framework to consider how it might be used to understand social resistance and generate potentially novel hypotheses that may be useful to both enhance the development of strategies to manage resistance and modulate change in socio-ecological systems.