In The Selfish Gene, originally published in 1976, author and renowned British evolutionary biologist Richard Dawkins expands upon American biologist George C. Williams’s 1966 critique Adaptation and Natural Selection. In his text, Dawkins describes the molecular gene as the fundamental unit of evolution. Through the study of animal behavior, he explores numerous examples of natural selection. Like Williams, Dawkins shares a gene-centric view of evolution.

Dawkins also extends Charles Darwin’s theory of evolution by investigating the progression of individual genes. Evolution applies to organisms and their genes, and either view could have equal validity. However, viewing evolution through the perspective of the gene opens new possibilities. Since Darwin, biologists into the 20th century gradually developed the genetic perspective of evolution. However, Dawkins makes it more explicit, to place it at the core of evolutionary biology.

According to Dawkins, genes developed as self-replicating molecules in Earth’s oceans. Among numerous molecules, these replicators rapidly copied their way to predominance. Due to competition over limited resources in their environment, replicators built increasingly complex machines to protect themselves. These machines now take the forms of plants and animals, including humans.

The machines, at the individual or group levels (such as a single organism or an entire species), contain large collections of replicators. According to Dawkins, the replicators themselves (genes) evolve over time, while their hosts (organisms) die out every generation. Through the constant mixing of genes in the gene pool of a species, surviving varieties become ever more prevalent. These “survival machines” (22), or organisms, represent a variation of the primeval soup in which the replicators first arose. From their inception as simple barriers to separate the genes from the environment, the survival machines have evolved into complex forms such as plants and animals.

Animals move through the environment, requiring a brain to coordinate. Muscles and other organs act as engines and other instruments. The brain replaces the genes in the fast action of the environment. Over time, brains could rebel against their controlling genes. The survival machines often depend on limited resources, forcing combat. More closely related machines contest more resources. Over time, animals and their genes settle into evolutionarily stable strategies.

More closely related survival machines share more genes. These “selfish genes” (22) produce machines to defend themselves, resulting in the appearance of altruistic individuals. For example, mothers know that they have many copies of their genes in offspring and therefore, invest heavily in nurturing. Parents face a trade-off between having more babies, “bearing,” and nurturing their young, “caring” (117). An appropriate mix will yield the most surviving offspring. This propagates the genes further, developing the genetic disposition to have the most suitable number of offspring.

Group selection has supported theoretical explanations for how animals could evolve to limit their own populations for the “common good” (3). However, Dawkins argues that all such arguments can be equally explained through the different mechanism of the selfish gene. According to the latter, genes produce survival machines that effectively predict how many offspring it is in their own interest to bear. Parents must divide their reproductive energy not only in the appropriate number of offspring, but also in the appropriate amount of “parental investment” (94) of food and time for each child. Because of the one-half genetic commonality between each parent and each child, genes evolve survival machines that serve themselves first and relatives second. When the benefit of “altruism” (9) towards an immediate relative is twice the benefit to a survival machine itself, animals instead act altruistically.

As genetic interests affect generational differences, the genes also influence sex differences. Males and females evolved to have different sex cells. Sperm are small and many, eggs are large and few. As a result of different sex cells, females have genetic incentives to have limited sex with select males, while males have incentives to have as much sex as they can. Particular environmental conditions result in a variety of mating strategies for males and females of different species.

Animals sometimes appear to behave altruistically. For example, birds give warning calls at risk to themselves. However, Dawkins shows that selfish genes have produced animals that increase their own survival. “Reciprocal altruism” (140), in which an act for another organism is paid back later, can become an evolutionarily stable strategy. Cheating and detecting cheaters may have resulted in human mental faculties.

Humans have complex cultures. In brains and media, cultural items get transmitted rapidly. Dawkins defines the fundamental unit of culture as the “meme” (143), analogous to the gene. Memes spread for their own selfish interests, as do genes. However, humans have foresight, and thus the capacity to rebel against their genes and memes. Mathematical games reveal that “nice” (157) behavior evolves, even from selfish genes. Cooperation yields mutual advantages, so organisms that regularly interact develop considerate, forgiving behaviors.

Genes cooperate within bodies and between bodies. Any behavior that a gene produces to increase its survival rate propagates the gene. This leads to the “extended phenotype” (175), the notion that genes can act throughout the environment. Genes in a single body can be considered “parasites” (179) of the body. They can also spread as viruses among other bodies. The reproductive organs of organisms form the main route of transmission.

Replicators, any molecules copying themselves, can arise spontaneously. Thereafter, they quickly spread. Copy errors result in variations, the best surviving to form subsequent generations. Over time, increasingly complex organisms form. Today, these plant and animal genes have replaced the soup of primordial replicators. Biologists can get fooled into seeing the genes as tools of the organisms, but The Selfish Gene shows how the “survival machines” are in fact vehicles for the replicators.