Widespread agreement currently exists regarding man's phylogenetic relationship to our closest living relatives, the great apes. Humans are generally regarded as forming a monophyletic group with the African apes, chimpanzees, bonobos, and gorillas, to the exclusion of the Asian orangutan. Despite this consensus, a few researchers continue to disagree with this popular account of hominoid evolution. The most recent and vocal critic of this phylogeny is Jeffrey Schwartz. In The Red Ape, Schwartz summarizes his unorthodox argument that humans and orangutans are sister taxa.
The book begins with an introduction to the natural history of the orangutan. Unfortunately, this section contains several factual errors, and as a result, the animal depicted in this section bears scant resemblance to the one we know living in natural environments and social settings. In rapid succession (pp. 12-14), Schwartz claims that orangutans possess a group structure beyond the level of solitary individuals, that male long calls function to attract potential mates, and that mating occurs during peak periods of estrus. All of these assertions are made to draw parallels between humans and orangutans, but none are supported empirically.
Following this inauspicious beginning, chapters 2 and 3 contain informative reviews of major fossil discoveries bearing on the evolution of humans and apes, respectively. The reviews are chronological, with accounts of major discoveries presented historically. In chapter 4, entitled "The Riddle of Relatedness," the author discusses and advocates the cladistic method to determine evolutionary relationships among organisms. This approach emphasizes that relatedness among animals should be ascertained on the basis of shared, derived characteristics. The cladistic approach is applied in chapters 5 and 6 to the problem of providing operational definitions for the order Primates and the superfamily Hominoidea.
In chapter 6 Schwartz presents his hypothesis explicitly: certain anatomical characteristics reflect the close phylogenetic relationship between orangutans and humans. Shared, derived characteristics held in common between humans and orangutans include low-cusped cheek teeth, thick molar enamel, and a single incisive foramen. Schwartz develops this theme more forcefully in the following chapter by presenting a long list of features shared uniquely between orangutans and humans. The list includes characteristics ranging from features of the basicranium to the lack of sexual swellings among females during estrus. The list is exhaustive and impressive. Nevertheless, the author never seriously entertains the alternative hypotheses that these traits have arisen in both taxa due to functional convergence or in response to similar developmental constraints. For example, it is possible that low-cusped cheek teeth and thick molar enamel represent a functional complex. This complex may have evolved in orangutans and humans as the result of unique feeding requirements on bark, seeds, or other hard