Toward a More Reliable Morphological Data Set for Phylogenetic Reconstruction

For decades, the relationships between different species have been discerned by way of a set of observable characteristics. Based on the similarity of certain observables, two species could be grouped together, along with other organisms that shared the same features. By these methods, scientists constructed a hierarchy of life. Taxonomy is the name given to the study and organization of different species. In parallel, relationships between species across time can also be deduced. Phylogeny is the study of genetic relationships between different species, and between the species their possible ancestors. These relationships were likewise inferred from observable characteristics present in modern and ancient organisms. The course taken by evolution has thus been charted using these morphological and physiological similarities. Over the past 10-15 years, there has been much discussion about the validity of these phylogenies. The source of the debate has been the emergence of scientific methods for studying and comparing species at the molecular and genetic level. The human phylogenetic hypotheses that have been around for the last few decades are now being thrown into disarray by the incongruent results of molecular phylogeny. Without a reliable phylogeny as supporting evidence, associated evolutionary hypotheses are on very loose footing. A recent study by Mark Collard and Bernard Wood finds several discrepancies between morphological and molecular phylogenies for extant higher primates 1. Cladistic analysis of cranial and dental evidence is commonly used for generating phylogenetic hypothesis about primates and their ancestors. Fortunately, two groups – the hominoids and papionins – have well-established molecular phylogenies. The hominoids are those higher primates most closely related to the fossil hominins, and include Homo sapiens. The papionins are an Old World monkey tribe comprising the baboons, mangabeys, and macaques. In comparing phylogenies, the assumption is then made that congruence between those that are morphological and those that are molecular indicates that equivalent hominin fossil evidence yields reliable phylogenies. The reliability of molecular phylogenies should not be questioned. First, phylogenetic relationships arise purely from genetic grounds, and morphological data is at best a qualitative map of those genes. Second, morphological characteristics can often be influenced by external stimuli and can thus become misleading. Third, molecular phylogenies for the particular groups in this study are supported by several different independent lines of research. Lastly, molecular phylogenetic methods have been successfully tested on groups of organisms that have a well-known phylogeny. In their study, Collard and Wood focused …