Tracing Our Lineage: Molecular among them. Three main relationships have Contributions to the Construction been suggested in the literature: a human- of the Human Phylogeny orangutan clade (Grehan and Schwartz 2009), a human-gorilla clade, or a human- chimpanzee clade (Satta, Klein, and Randa Stringer Takahata 2000). While each of these interpretations has had merits, it has been Introduction shown that the molecular evidence clearly One of the fundamental questions demonstrates the existence of a human- anthropology has long sought to answer is chimpanzee clade (Ebersberger et al. 2007). how the human species came to be what it is One of the most prominent studies in today. Though this debate has been going support of the human-orangutan relationship on for centuries, recent developments in is that of Grehan and Schwartz (2009). molecular biology have provided a new and They examined the extant hominids using in many ways more definitive basis of humans (H. sapiens), gorillas (Gorilla), evidence for analysis. This paper will chimpanzees and bonobos (Pan), and examine the manner in which the expanding orangutans (Pongo) as the ingroup taxa field of genetics has allowed us to enhance (those being analyzed in the study). A our understanding of how we came to be. compilation of behavioural, structural, and Through determining our relationship with physiological features was developed using the extant non-human hominids, providing traits that had been generated for previous novel evidence regarding our interactions studies of hominid relationships. Using with Neandertals, and invalidating the these characters the authors concluded that concept of race, genetic analysis has been the most parsimonious tree produced a invaluable to biological anthropology and in monophyletic clade containing humans and defining who we truly are as a species. orangutans, closely related to a sister group of chimpanzees and gorillas. Gibbons were Our Relationship to Extant Hominids the next closest relation, with various There has been a great deal of debate monkey species providing an outgroup. among biological anthropologists as to the Grehan and Schwartz based their exact nature of our relationship with the conclusions primarily on morphological extant hominid species, which include data, arguing that this is in fact a better gorillas, chimpanzees, bonobos, and standard than molecular analysis because it orangutans (Grehan and Shwartz 2009). is not based on unproven assumptions. While these species are widely However, as more and more molecular acknowledged to be our closest extant evidence is amassed, it has become clear relatives, disagreements arise when debating that the methodology of this study is to which of these species we are most outdated and cannot refute the abundant closely linked phylogenetically. Early genetic findings that counter this conclusion. conclusions were based primarily on Thomas Huxley (1863) suggested in morphological evidence (e.g., McHenry and Evidence as to Man’s Place in Nature that Corruccini 1981; Shea 1983), but with the gorillas could be the closest extant relatives advent of genetic technology, comparisons to humans. Since the advent of molecular at the molecular level become an analysis it has become increasingly apparent increasingly powerful method through that there is little evidence supporting this which to construct the phylogeny of the notion. Early evaluation of mtDNA extant hominids and establish our place sequence data by Kishino and Hasegawa sharing a distinct common ancestor. This (1989) demonstrated that orangutans are an study made use of the advances in genome outgroup of the extant great apes as sequencing that have provided a full compared to humans, chimpanzees, and sequence of the human genome, a draft gorillas. However, the study was unable to sequence of the chimpanzee and rhesus conclusively determine the cladistic ordering genomes, and extensive preliminary shotgun of the final three hominid species. Ferris et sequencing of the orangutan and gorilla al. (1981) had already proposed a phylogeny genomes. By examining 23,210 sequence based on mtDNA analysis in which alignments from these primates (using the chimpanzees and gorillas were the closest in rhesus monkey as an outgroup), they ancestry, with humans taking a more distant determined the percentage of alignments relationship to this sister pair. Subsequent that would support each of the possible studies showed that depending on the choice phylogenetic trees that could be created of mtDNA genes used for evaluation, either from various ancestral arrangements of these a human-chimpanzee clade, a human-gorilla species. Of these alignments 13,869, a clade, or a chimpanzee-gorilla clade could 59.75% majority, suggested a human-chimp be supported (Satta et al. 2000). This gave cladistic arrangement, with gorillas being rise to the possibility of a trichotomy in the next closest relative. Of the ingroup, which all three species were equally related. orangutans were the most distantly related to While the trichotomy proposal humans, with the rhesus monkey seemed to fit the data at the time, further maintaining its outgroup status. This information on the nature of genetic extensive examination of such a large evolution provided the reason as to why any sample of sequence alignments has come as of the three clades could be supported close as is currently possible to determining depending on the genes examined: gene the monophyly of the chimp-human clade. trees are not necessarily the same as species Although publication of the full trees (Nichols 2001). Although phylogenies genome sequences of the gorilla and are generally drawn with distinct branching orangutan may in the future yield unforeseen points, these apparent speciation events may results that could change our interpretation not reflect the divergence of ancestral genes of the hominid phylogeny, at this point it (Nichols 2001). Certain loci may diverge at seems that our closest extant relative is in different times, resulting in conflicting fact the chimpanzee. Molecular genetics has interpretations when attempting to construct been invaluable in the construction of this species trees using genetic data (Nichols phylogeny. It is imperative that we 2001). Since these discrepancies are understand our relationship with the extant generally small, analysis of a greater number hominids in order to better reconstruct our of sequence alignments provides a sample own evolutionary history. size large enough to overwhelm these differences and produce a more accurate Our Relationship to Neandertals species tree through molecular analysis Since the discovery of the first (Satta et al. 2000). Neandertal specimens, anthropologists have A recent study by Ebersberger et al. been debating two forms of the same (2007) used this technique to demonstrate question: whether Neandertals are a member that humans and chimpanzees show the of our species, and whether, during our closest evolutionary relationship and period of coexistence, Neandertals and constitute a monophyletic clade, therefore humans interbred. The answers to these questions have implications not only in Preliminary genetic analysis came reconstructing the path of evolution that led from the sequencing by Krings et al. (1997) to modern humans, but also in of hypervariable region 1 (HVR1) in the understanding our current genetic make-up. Neandertal mitochondrial genome. The If Neandertals and humans did interbreed, it comparison of this mtDNA sequence to that is possible that components of our genome of modern humans revealed 27 genetic were in fact acquired from Neandertals mutations (24 transitions, two transversions, through this mechanism. and one insertion), all corresponding in Two main models have addressed nature and location to what would be the question of our relationship with expected in typical mtDNA evolution. The Neandertals. The Multiregional Continuity average number of mutations generally Model suggests that Homo erectus migrated observed in this region within modern out of Africa one to two million years ago humans is only eight (Tattersall 1998). This and since then there has been concurrent means that the number of mutations between evolution of modern humans across the Old humans and Neandertals is approximately World through constant gene flow (Fohran three times that seen among humans. This et al. 2008). Inherent in this model is the level of variation is supportive of The idea that humans and Neandertals were Recent African Origins Model. Other members of the same species and would sequencing projects focussing on this same have interbred. The Recent African Origin region have found similar results, Model suggests that modern Homo sapiens confirming the original study (Weaver and evolved once in Africa, migrating out to the Roseman 2005). rest of the Old World 100 to 200,000 years Further mtDNA sequencing by ago and replaced all existing hominins with Green et al. (2008) focussed on the COX2 no interbreeding (Fohran et al. 2008). gene, which encodes subunit 2 of While the original debate between cytochrome c oxidase, a protein involved in these models relied on morphological mitochondrial electron transport. This gene evidence, advancements in genomics have has been shown to be subject to particularly provided a new and effective manner by quick evolution in primate lineages, which which to analyze the possibilities. Both makes it especially useful for analysis. mitochondrial and nuclear DNA have been Since our