Darwin and His Bears discusses some of the most important principles of evolutionary theory, as developed by Charles Darwin and subsequent evolutionary biologists, including Ernst Mayr, Edward O. Wilson, and Stephen Jay Gould.
Among the various theories treated in this book are:
- Speciation (the splitting of one species into two or more species) through geographic isolation, as has occurred, for example, among many of the birds, reptiles, and plants inhabiting the different islands of the Galápagos Archipelago.
- Darwin’s (1859) seminal theory of evolution by natural selection, which involves the differential survival and successful reproduction by individuals possessing adaptive morphological or behavioral traits.
- The principle of adaptive radiation, whereby species become modified to occupy diverse ecological niches.
- Theories of island biogeography, according to which the presence or absence of species, as well as some of their adaptive traits, are dictated by geographic factors such as island size and distance from the mainland (MacArthur & Wilson, 1967).
- Ernst Mayr’s (1954) theory of genetic revolutions in small, peripherally isolated populations.
- Punctuated equilibrium (Eldredge & Gould, 1972), which posits that evolution occurs rapidly during episodes of speciation and then involves much longer periods of stasis.
- Ernst Haeckel’s (1866) highly influential, but mistaken, theory that “ontogeny recapitulates phylogeny” (the biogenetic law)–a theory claiming that embryos pass through the adult stages of all their ancestors. As discussed in Chapter 7 of Darwin and His Bears, this theory inspired Sigmund Freud’s now-discredited ideas about psychosexual development, including Freud’s claim that some neuroses are caused by repressed phylogenetic memories.