The recognition and evaluation of homoplasy in primate and human evolution

Abstract

Homoplasy has been a prominent issue in primate systematics and phylogeny for as long as people have been studying human evolution. In the past, homoplasy, in the form of parallel evolution, was often considered the dominant theme in primate evolution. Today, it receives blame for difficulties in phylogenetic analysis, but is essential in the study of adaptation. This paper reviews the history of study of homoplasy, methods of defining homoplasy, and methodological and biological factors that generate homoplasy. A post hoc definition of homology and homoplasy, based on patterns of character distributions and their congruence or incongruence on a cladogram, is the most consistent method of recognizing these phenomena. Defined this way, homology and homoplasy are mutually exclusive. However, when different levels of analysis are examined, it is seen that homoplasy at one level, such as adult phenotype, often exists simultaneously with homology at a different level, such as developmental process. Thus, in some cases, patterns of homoplasy may point to underlying similarities that reflect the shared heritage of a particular clade. This is an old concept that is being renewed on the strength of recent trends in developmental biology. Factors that influence homoplasy include character definition and a host of biological factors, such as developmental constraints, allometry, and adaptation. These interact with one another to provide explanations of homoplastic patterns. Because of the repetition of events, explanations of homoplastic features are often more reliable than those for homologous features, and serve as effective tests for hypotheses of evolutionary process. In some cases, particular explanations of homoplasy lead to generalizations about the likelihood of homoplasy in a type of structure. The structure may be adaptive or highly epigenetic, or it may belong to an anatomical system considered to be more prone to homoplasy than others. However, our review shows that these generalizations are usually based on theory, and contradictory expectations can be developed under different theoretical models. More rigorous empirical studies are necessary to discover what, if any, generalizations can be made about the likelihood of homoplasy in different types of characters.

Bringing Up Baby: Developmental Simulation of the Adult Cranial Morphology of Rungwecebus Kipunji

“…The mangabey phenon contrasts with the large-bodied, long-faced, predominantly terrestrial ''baboons,'' Mandrillus, Papio, and Theropithecus. The extensive homoplasy implied by the phylogenetic distribution of these ecomorphs has made African papionins a touchstone for the study of primate morphological variation and evolution (Lockwood and Fleagle, 1999;Collard and O'Higgins, 2001;Singleton, 2002;Leigh, 2007).…”

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“…Since directly observable data on behavior or soft tissue anatomy generally do not preserve in fossil material, paleontologists often utilize the phylogenetic species concept (although this practice has been sharply criticized, e.g., Hennig [1965]; netic analysis at the species level (Harrison 1993;Trinkaus 1995;Wolpoff and Crummett 1995). For example, it is difficult to determine, in closely related taxa, whether shared characters are due to homology or homoplasy (Lockwood and Fleagle 1999;Wood 1999), or to what degree apomorphies are affected by sample size or inter-or intrapopulation variation (Hawks 2004). A more problematic issue when using cladistic analyses in modern human origins research is that groups must be separated a priori into discrete taxa as a requirement of the methodology.…”

“…Cladistic classification requires that all taxa be crisp sets, monophyletic and mutually exclusive in their morphological patterns (Eldredge and Cracraft 1980;Hennig 1966;Mayr 1981;Olsen 1978;Wiley 1981). The characters used to compare taxa are features identifiable on the skeleton either as qualitative features or quantitative measurements/ratios (Lockwood and Fleagle 1999). Cladists trace evolutionary relationships between taxa through the identification and comparison of synapomorphies, avoiding character similarity due to sympleisomorphy or homoplasy (Delson et al 1977;Forey et al 1992;Grande and Rieppel 1994;Hennig 1966;Quicke 1993).…”

The relative correspondence of cranial and genetic distances in papionin taxa and the impact of allometric adjustments

“…Previous studies of cranial morphology in the papionin taxa have suggested relatively high levels of craniomorphic homoplasy in this tribe (Fleagle and McGraw, 1999;Lockwood and Fleagle, 1999;McGraw and Fleagle, 2006;Gilbert, 2007;Gilbert et al, 2009). Phylogenetic studies based on traditional morphometric variables resulted in three primary groups of papionins initially being recognized: mangabeys, baboons, and geladas (Thorington and Groves, 1970;Jolly, 1972;Szalay and Delson, 1979;Strasser and Delson, 1987).…”