Encyclopedia of Evolutionary Psychological Science

Living Edition
| Editors: Todd K. Shackelford, Viviana A. Weekes-Shackelford

Adaptation and Natural Selection

  • Nora BalboaEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-16999-6_1872-1


In his book, Adaptation and Natural Selection, George Williams (1966) discusses what is meant by the term “adaptation” and what can be done to further the study of that phenomenon. Throughout the course of the book, he provides an overview of past research on the subject and challenges misconceptions, such as group selection, which he believes to be misguided attempts at understanding adaptation.


George Williams’ 1966 book, Adaptation and Natural Selection, seeks to define what is meant by researchers discussing the adaptation of species and clarify differences in understanding of the term and the process it describes. The main purpose of adaptation, as Williams understands it, is to promote the survival of the individual and that individual’s ability to reproduce in order to preserve their genes. Through the process of evolution, adaptations that are useful for the survival of the individual are retained and passed on to future generations. Contrary to the beliefs of some other scientists at the time, however, Williams asserts that such adaptations do not necessarily make for a more complex organism with more complex DNA; rather, adaptations are substituted in, not added to, an ever-increasing cumulative DNA. Adaptation, he argues, does not necessarily progress the species to a more complex one, but a more fit one.

Another key concept outlined by Williams is the difference between the passing on of genotypes and phenotypes. This distinction proves important in his discussion of the presence or lack thereof of group selection. He argues that while an individual’s environment can affect the phenotypic expression of their genes, that environment is not necessarily influencing which genotypes will be passed to the next generation. This is because while the environment can cause variation in the expression of phenotypes, that expression is not what is passed on. Though several organisms might express a genotype differently, they all possess the same genotype, and in the end, it is that genotype that is passed to the next generation. The fact that it is the genotype, and not the phenotype, that is passed through generations provides a foundation for Williams’ criticism of the idea of group selection.

To distinguish between individual and group level selection, Williams refers to organic and biotic adaptation, respectively. An adaptation that produces modifications to the individual that aids in its survival and reproduction is referred to as organic adaptation, which leads to the evolution of the species. In contrast, a biotic adaptation is an adaptation that promotes group survival and cannot be explained by organic evolution. He argues that while biotic adaptation might occur, it is difficult to find an instance where what appears to be biotic, or group, evolution is actually the cumulative result of individual adaptations. Whereas it might seem like a group has adapted together, the truth in most situations is that the group is composed of adapted individuals, and this individual adaptation is what contributed to the survival of the group.


Williams concludes that in order to be truly useful to the study of organisms and their evolution, the term “adaptation” needs to be clearly defined and the field of study related to the adaptive traits of organisms similarly narrowed down. Previous researchers, he argues, have applied the term too liberally, labeling traits that do not have a true directed purpose as adaptations when they are not. Rather, a true adaptive trait should be defined as one that serves a tangible function produced through natural selection and could not have happened by chance, citing the development of the eye as one such adaptation; it is obvious that the eyes of organisms have an expressed purpose, which has been honed over time through selection processes and is not a chance development that happens to benefit the organism. Once this more narrow view of what an adaptation is accepted, then a new field of study – which he tentatively refers to as teleonomy – will be able to emerge and dive deeper into what constitutes an adaptation and how they function.



  1. Williams, G. C. (1966). Adaptation and natural selection: A critique of some current evolutionary thought. Princeton: Princeton University Press.Google Scholar

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Authors and Affiliations

  1. 1.Kansas State UniversityManhattanUSA

Section editors and affiliations

  • Gary L Brase
    • 1
  1. 1.Department of Psychological SciencesKansas State UniversityManhattanUSA