By:Kieran P. McNulty(Evolutionary Anthropology Lab, University of Minnesota)© Education

Citation:McNulty,K.P.(2016)Hominin Taxonomy and also Phylogeny: What"s In A Name? Education Knowledge7(1):2




At the the majority of fundamental level, human advancement is articulated via classifications of, and also evolutionary relationships among, hominin species. This short article presents a simple taxonomy and phylogeny of hominins, yet likewise additionally explores the factors that conuncovered systematics in humale evolution.

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The exercise of biological classification showed up early in the advancement of life: Is this safe to eat/not safe to eat? Is that a predator/not a predator? Are these potential mates/not potential mates? It is in our, then, to classify our surroundings. Within the context of biology this exercise takes on special prominence, as scientists from many kind of biological self-controls work towards a solitary classification device that incorpoprices all organisms that have ever lived. Both the practice and also the product of this grand biological classification are called taxonomy.

The a lot of extensively offered taxonomic device was formalized by Carolus Linnaeus and also comprises a basic nested pecking order wherein equivalent organisms team together at one taxonomic rank, and also those teams cluster into successively broader teams at greater ranks. Figure 1 shows a taxonomy of humale ancestors and their extant Afrihave the right to ape loved ones. This nested pecking order enables different levels of similarity to be stood for at different ranks. Note, but, that Linnaean taxonomy predates contemporary evolutionary theory; whereas Linnaeus organized living organisms according to different levels of similarity, it was Darwin and also others who described these differing levels of similarity through prevalent ancestry. The even more very closely associated 2 teams are, the more similarities they are most likely to share. The series of evolutionary relationships among a group of organisms is termed phylogeny.

Linnaean ranks are detailed across the peak, through vertical lines to show the indentation of matching taxon names; ranks and taxa are likewise correlated by shade. Ranks over the genus level encompass the correct taxon name (always beginning with a resources letter) and also the common name in parentheses. Hence, to refer to the team of Afrihave the right to apes and people, one can say either the Homininae or the hominines. The genus and species names (typically referred to as the "scientific name") are constantly composed in italics, and the genus starts through a resources letter whereas the species is always lowersituation. Note that the species name is never before written alone, and therefore each species is predelivered by an abbreviation for its genus. Although nearly all employees identify the close connection between Homo and Pan, to the exclusion of Gorilla, tright here is not yet a extensively supplied taxonomic rank to demarcate this association.

It is generally understood that taxonomy need to reflect phylogeny - organisms have to be grouped according to their evolutionary background, their relatedness. This makes intuitive sense bereason prevalent ancestry is the just aspect that unites four billion years of life on Earth. This link between taxonomy and also phylogeny implies that new explorations or other data that adjust our expertise of evolutionary background regularly lead to the shuffling of taxa and also of taxonomic names.

An fantastic example of this shuffling is the readjust in consumption of the term "hominid." Traditionally, just huguy ancestors were put in the household Hominidae (and thereby described as hominids). This reflected a watch that human beings are substantially different from the great apes, which were placed in the Family Pongidae (pongids) (Figure 2a). However before, overwhelming hereditary proof has given that demonstrated that people, primates, and gorillas are much even more very closely regarded each other than to the orangutan (e.g., Sarich, 1971; Caccone & Powell, 1989; Ruvolo, 1994). Therefore, tbelow is no genetic assistance for grouping the excellent apes together in a unique group from human beings. For this factor, many kind of researchers now location all species of great ape and human within a solitary household, Hominidae - making them all proper "hominids" (Figure 2b).

(a) A typical phylogeny of contemporary apes, where orangutans (Pongo), gorillas (Gorilla), and also monkeys (Pan) were thmust be extremely carefully associated. In this system the lesser apes, gibbons and siamangs (Hylobates), are put into their very own household of hylobatids; great apes are grouped together in the Pongidae (pongids), and also just the human lineage was had in the Family Hominidae, the hominids. (b) This is a modern understanding of ape phylogeny, where the excellent apes no much longer recurrent a distinct team from people. Here, tbelow is no assistance for a sepaprice Family Pongidae and therefore excellent apes and also their ancestors are grouped within the Family Hominidae. For this reason, the term "hominid" is currently commonly applied to all great ape and also humale species not just the lineage of people.

Such taxonomic transforms have downstream impacts as well: Afrihave the right to apes and humans are currently distinguished from orangutans at the subfamily rank Homininae (hominines), and also the human family tree is separated at an also lower rank of Tribe Hominini. Therefore, the common term for the lineage of fossil and also modern people is "hominin." Furthermore, the standard term "australopithecine," which grouped Australopithecus and Paranthropus in the subhousehold Australopithecinae, becomes invalid under this revised taxonomy; in the context of Linnaean taxonomy, one cannot nestle a higher-ranked subfamily (Australopithecine) within a lower-ranked people (Hominini) (check out Figure 1).On one hand, this change in terminology over the years illustrates the appropriate development of scientific research, by which new evidence around evolutionary history helps to refine our taxonomic models. However, the essential linguistic shift has actually been slow to get acceptance among some researchers. As well, the popularity of terms favor “hominid” and also “australopithecine,” which seeped into public awareness in the 1960s-70s, suggests these terms will most likely persist in their traditional interpretations for connecting through the public.

One version of hominin evolution is shown by the phylogeny in Figure 3, presented right here as a automobile for discussion fairly than a durable hypothesis. An noticeable point of contention is the condition of the earliest hominins, known from just small isolated samples; relationships both among these species and to the later on hominins are not yet readdressed. And, while other branches of the huguy evolutionary tree are intensely debated in the literature, the usual signarticles of phylohereditary uncertainty (e.g., daburned lines, alternative branches, question marks) have actually been omitted from Figure 3 for simplicity. Instead, a few of these problems are highlighted listed below, especially in the conmessage of taxonomic and also phylogenic obstacles: family tree, variation, and organic intricacy.

Approximate geological age ranges are had for each. Black lines suggest a phylogenetic link, though these relationships are proposed primarily for discussion and also are not well-tested hypotheses. Several species are left unconnected due to the many possible methods in which they could pertained to the various other species. The box highlights a area of the phylogeny that is supplied in Figure 3.

Five species of Australopithecus are well-known here, though brand-new discoveries are most likely to add to this number. There is great evidence that A. anamensis and also A. afarensis reexisting evolution within a vast lineage (Kimbel et al., 2006), however various other relationships in the genus are not well construed. It may be that the genus is an amalgamation of stem species that are not very closely related (see below), though they seem to share a widespread adaptive grade. Many researchers would agree that both Paranthropus and also Homo progressed from some Australopithecus-choose ancestor(s), though which is still contentious. This principle of family tree, however, presents difficulties for our initiatives to enhance taxonomy to phylogeny. For example, if the phylogeny in Figure 3 were correct, then A. africanus and its descendants would certainly be even more closely pertained to the genus Homo than various other species of Australopithecus; additionally, A. garhi would certainly be even more carefully related to Paranthropus. How, then, can our taxonomy be made to reflect these evolutionary relationships?

The most prevalent solution is via dividing. For instance, Figure 4a illustrates the cladogenetic relationships among the boxed species in Figure 3, through "Australopithecus" species here distributed among 3 genera. Because the genus name Australopithecus is particularly associated via Au. africanus, this species and its descendant Au. sediba retain that genus name. "A." garhi is moved to Paranthropus to reflect that relationship, while "A." afarensis calls for a new genus designation, Praeanthropus (watch, e.g., Strait et al., 2007). This horizontal dividing across the species-level of our taxonomy likewise implies a vertical separating at better ranks, where each node (junction of branches) on our cladogram calls for a distinctive rank to denote a sepaprice evolutionary relationship. Hence, to precisely replicate the relationships presented in the cladogram would need adding 6 extra ranks (and also their attendant taxon names) in between the people and also species levels representing the historical splitting occasions in this family tree. In this means, a taxonomic hierarchy have the right to be made to exactly reflect the cladogenetic relationships of evolutionary background.

(a) A cladogram depicting feasible phylohereditary relationships among these species, and the new genus desigcountries (cf. Figure 1) that result; (b) evolutionary diagram of the very same species, yet depicted as a collection of evolving populations rather than cladohereditary splits; the horizontal line suggests the slice of time stood for in (c); (c) a time slice from the phylogeny in (b) reflecting the relationships in between populaces simply after they begin to diverge.

This approach leads to a curious theoretical dilemma, however. By arranging our taxonomic names to enhance phylohereditary relationships, we end up organizing species according to events that happened after their existence rather than their contemporaneous biology. Consider, for example, the phylogeny in Figure 4b, depicting these populaces evolving with time. Considering a time slice from this phylogeny (Figure 4c), the two populations of Au. africanus would certainly be - by any contemporaneous meacertain - the exact same species. But, bereason one populace later developed right into species of Homo, researchers at a contemporary vantage are inclined to carry that population into this genus. Such action can much better reflect the succeeding phylogenetic relationships among descendants, however does not fully account for the biological context of the organisms in question.

The divide between australopiths and also the genus Homo was when reasonably clear, the latter team distinguished by a markedly larger brain. Leacrucial et al."s (1964) addition to Homo of the smaller-brained H. habilis, but, blurred this boundary and also sparked dispute over the scope of variation that could be accommodated within the human genus. With the discovery of many kind of even more specimens of early on Homo, however, these disagreements offered method to various other taxonomic considerations: just how many species were represented in the varied sample of small-brained Homo? can they all be accommodated within the single species H. habilis?

Amongst fossils, variation within a varieties is largely a taxonomic worry rather than a phylogenetic one ssuggest bereason fossil preservation is hardly ever good enough to build robust evolutionary hypotheses for a huge number of individual specimens. Unfortunately, tbelow are no clear guidelines regarding the amount of variation appropriate to any taxonomic team, and also no definitive means to test whether species allocations are correct. Researchers frequently use variation within modern species as benchmarks for acceptable arrays and patterns of variation (e.g., McNulty, 2003, 2005; Baab et al., 2010), but even this have the right to be problematic: variation in extinct species require not be similar to variation in modern-day ones (Kelley, 1993). This problem may be particularly acute in hominin researches, wright here variation in living comparator species, such as gorillas and primates, might have actually been radically influenced by decreasing populations.

What, then, is the of variation in early Homo? A number of comparisons to modern-day apes and humans have discovered that the sample traditionally grouped in H. habilis exceeded the variation expected within a single modern-day species (e.g., Stringer 1986; Bilsborough and Wood 1988; Liebermale et al. 1988; Chamberlain 1989; Kramer et al. 1995). This led Alexeev (1986) to propose a brand-new species, H. rudolfensis, to accommoday the bigger specimens of this sample, retaining the smaller sized ones in H. habilis. With one huge and one small species of early on Homo, the logical counter dispute was that the sample represents a solitary, sexually dimorphic species (e.g., Howell 1978); Wood et al. (1991), however, gave tentative proof that fads of variation within the broad sample of early Homo are not continuous with recognized trends of dimorphism. For this factor, paleoanthropologists have actually mainly welcomed the presence of two species of early on Homo, and also tbelow might be proof for extra taxonomic diversity (Smith and also Grine, 2008).

As a last twist in the taxonomic narrative, Wood and Collard (1999) provided a systematic justification for rerelocating H. habilis and H. rudolfensis from Homo entirely, and also placing one or both right into Australopithecus (watch additionally Leacrucial et al., 2001). Thus much, yet, their proposal has actually not acquired broad acceptance.

One of the oldest disputes in paleoanthropology revolves around the taxonomic condition of the neanderthals. While many researchers agree that the distinctive neanderthal morphology shows a level of separation from other modern hominins, tright here is disagreement over whether neanderthals belengthy within H. sapiens or in their own species, H. neanderthalensis. Tbelow is ample morphological justification for recognizing a distinctive species (e.g., Harvati et al., 2004), and early on analyses of prehistoric mitochondrial DNA from neanderthals supported this conclusion (e.g., Krings et al., 1997). More recently, yet, sequencing of the nuclear genome has actually presented that modern-day humale populations outside of Africa retain up to 4% of distinctive neanderthal genes (Environment-friendly et al., 2010). If one specifies a varieties as populaces of interbreeding organisms (a criterion well-known as the organic species concept), then the existence of neanderthal genes among contemporary humans argues strongly for including them within H. sapiens, because it indicates that contemporaneous neanderthals and anatomically contemporary humans were interreproduction.

The instance of the neanderthals demonstprices a last hurdle in the conventional exercise of taxonomy and phylogeny: biology does not constantly adright here to our simplistic models. Our choice for arbitrating discrete taxonomic teams and instantaneous phylohereditary splits ignores the continuity and intricacy of organic development. Undoubtedly, one of the the majority of compelling demonstrations of evolution and common ancestry is precisely the lack of strict demarcations in between carefully connected species: dogs and also wolves interbreed; various moncrucial species hybridize; also the mule (or hinny) deserve to develop offspring, albeit rarely. Such blurred borders are specifically what would be expected from populaces that consistently evolve and diverge over time. This organic truth, but, plays havoc through notions that evolutionary lineages cleave instantaneously, or that we have the right to perfectly circumscribe groups of organisms into discrete taxonomic teams.

Did neanderthals separation right into a separate species or were they part of our direct lineage? The answer is more than likely "both." Refertile isolation, and also thereby speciation, is a procedure through which populations suffer degrees of infertility - behavior and structural impediments, lessened hybrid vicapacity, gametic incompatability, and so on. - over many generations. In this sense, lineperiods may not cleave so a lot as reticulate, through the network of hereditary exreadjust in between populations dissipating over time. Even in neanderthals, who were most likely geographically isolated from the modern-day huguy lineage, the capacity to interbreed was persistent over hundreds of hundreds of years (Environment-friendly et al., 2010). However, via neanderthal DNA offering maybe the just opportunity to directly test whether an extinct pre-contemporary hominin interbred through modern-day H. sapiens, I am inclined right here to group neanderthals within our species.

We research huguy family tree not ssuggest to have actually labels for museum exhibits, however quite to illuminate the facility story of morphological, physiological, behavior, cognitive, and also social alters that gave climb to contemporary humans. Hence, taxonomy in itself is not of straight interest. Coupled through its primary use as a substitute for phylogeny, taxonomy may seem basic to disregard. Without a doubt, if one functioned via just contemporary species - that have actually finish anatomies, DNA sequences, behaviors - it could be feasible to rely completely on phylogenetic relationships to organize specimens right into systematic groups.

Not so in the examine of fossils, however, wbelow finding any remnant of ancient species is rare, and also finding pieces that are reasonably undamaged is extraordinary. Lacking adequate anatomy for durable phylohereditary analyses of each bone fragment in a examine, it is taxonomic hypotheses that develop the organic basis for organizing fossil samples. Within paleosociology, then, taxonomy still plays 3 important roles:

1. Alpha-taxonomy. The sorting of individual specimens into species is possibly the many vital role of taxonomy in modern-day paleoanthropology. In a sample of bone fragments that consists of various pieces of anatomy as well as individuals of various size, age, sex, geological antiquity, and perhaps species, it is alpha-taxonomy that gives the justification for uniting some specimens right into groups while separating others - usually through referral to durable extant models of within-species variation. Importantly, because virtually all paleoanthropological study is based on taxonomic hypotheses, either clearly or implicitly, transforms in the underlying taxonomy have actually the capacity to greatly impact our interpretation of human evolution.

2. Mediating biologically systematic comparisons across space/time. Beyond the species level, taxonomic analyses administer a system for comparing bigger groups of fossil organisms. Working in the fossil document implies analyzing samples from different areas, various times, and known at different phylogenetic reoptions. Yet, that resolution determines the organic coherence of the phylohereditary groups: a extremely refixed area of a phylogeny can encompass very closely connected fossil species whereas an unresolved section can pool a a lot larger variety of organisms. Taxonomic hypotheses allow researchers to maintain some level of uniformity in comparisons across such huge teams, regardless of the phylogenetic resolution.

3. Communication. One of the biggest effects of Linnaeus"s taxonomy remained in facilitating communication in the scientific community. This is still important now, and also there is presently no generally accepted automobile to replace it. The basic terminology of taxonomy is additionally recognizable to the general public, and it is via such terms that research is made widely easily accessible. If the understanding produced through study into numerous years of human evolution is to have actually any kind of impact past the walls of the academy, then typical taxonomic labels will certainly most likely keep a area in paleoanthropology.

One of the prevalent plaints leveled against paleoanthropologists is that they are constantly re-arranging the humale evolutionary tree. Undoubtedly, it does seem that eextremely considerable new fossil is purported to "entirely change our expertise of huguy development." In truth, however, hominin phylogeny has actually been reasonably secure over the last 2 decades, despite considerable and also contentious brand-new explorations. Comparing phylogenies publimelted in the early 1990s to those showing up in 2012 mirrors a remarkable level of conformity. This suggests that - at leastern in broad strokes - our hypotheses about the advancement of the huguy family tree are sensibly durable.

Consider again the sample of hominin species through time, yet concentrating rather on the 3 well-sampled genera: Australopithecus, Paranthropus, and Homo (Figure 5). Substantial fossil samples from each have actually been accumulating for practically a century - longer, in the situation of fossil Homo. The background of researches on these specimens geneprices an excellent deal of stabilizing inertia to the standard relationships displayed below. While specific relationships in between these groups, and the phylohereditary relationships within them, are still far from readdressed, the in its entirety plan of Australopithecus, Paranthropus, and Homo appears reasonably stable; indeed, any alters to this arrangement are most likely to be, well, taxonomic.

A reiteration of the hominin species distributions, however emphasizing even more broadly the fundamental relationships among Australopithecus, Paranthropus, and Homo. Each ellipse encircles the species that belengthy in a genus, yet additionally extends to overlap via various other species that have actually been implicated in arguments over the genus. Hence, the regions wright here two or three ellipses overlap are most likely to represent essential locations for proceeding study.

That being shelp, which facets of paleoanthropological study are a lot of likely to have a major influence on our knowledge of huguy evolutionary relationships? The prepared answer is from new explorations. Findings such as the fossil "hobbits" in Flores (H. floresiensis) and the enigmatic Homo species from Dmanisi have dramatic ramifications for huguy advancement, and also the definition of these has actually yet to fully affect hominin phylogeny. The condition of the earliest hominins is also in a state of flux, and brand-new discoveries at the base of the hominin phylogeny will certainly sucount be felt up in the better branches. Perhaps the biggest potential for revising our interpretation of human development, however, comes from some of the much better recognized taxa. Referring aobtain to Figure 5, the ellipses have actually been drawn so as to incorporate recurring taxonomic and phylogenetic arguments appropriate to each genus. As an heuristic device, then, the regions wright here these ellipses overlap are likely to develop the best influence on our knowledge of humale evolution. Readdressing these relationships - determining which species inevitably belengthy to which genera, and just how those genera are connected - has actually the potential to transform our understanding of human origins and also diversification.

Australopiths: a general term generally supplied in referral to species of Australopithecus and Paranthropus. This is not a formal taxonomic name and therefore does not need to adhere to the strict rules of biological nomenclature.

Biological species concept: This is the many typically offered interpretation of a "species," through which populations of organisms are figured out to belong to the exact same species if their members interbreed and create viable offspring.

Cladogenetic: adjective referring to evolution through dividing events. If a population diverges right into two branches which thereafter evolve separately of one another, this is referred to as cladogenesis (or, cladohereditary evolution). If a populace evolves with time without splitting into multiple branches it is dubbed anagenesis (or, anahereditary evolution).

Cladogram: a branching diagram that represents just phylohereditary relationships among organisms (i.e., it does not encompass geological age or other contextual information). Formally, a cladogram is produced with cladistic analysis of a team of organisms, which determines evolutionary relationships making use of only derived (evolved) attributes that are common among at least some members of a group.

Typical ancestry: the common evolutionary background of all living organisms ago to a solitary beginning.

Gametic incompatibility: a barrier to sex-related remanufacturing wbelow the sex cells (gametes) of a male (sperm) and also female (egg) are as well different to allow fertilization. Once 2 populaces have diverged and also begin evolving individually, inevitably their members will certainly become incapable of interreproduction as a result of gametic incompatibility. One instance of this can be if evolution results in various numbers of chromosomes in the 2 populaces so that their members cannot interbreed (note that various chromosome numbers does not always bring about gametic incompatibility).

Mitochondrial DNA: hereditary indevelopment that is linked via a cell"s mitochondria rather than its chromosomes. The mitochondria resides outside of the cell nucleus (within the cytoplasm) and are inherited only from the maternal line in sexually redeveloping organisms.

Node: Evolutionary relationships are regularly represented by tree-prefer patterns of branching lineeras. A node is where 2 or more branches come together at a allude, and therefore it represents the last common ancestor common by those teams prior to they diverged.

Nuclear genome: The nuclear genome is made up of the DNA from an organisms chromosomes, which reside in the cell nucleus. In sexually reproducing creatures, the nuclear genome consists of genes from both parents.

Phylogeny: the evolutionary relationships among, or evolutionary background of, a group of organisms.

Sexually dimorphic: Adjectival phrase referring to differences in dimension and form in between males and also females of a types.

Taxon: Any team from any rank of the Linnaean classification have the right to be primarily described as a taxon. Therefore, the Family Hominidae is a taxon, as is the species H. sapiens and also the Order Primates. The plural is taxa.

Taxonomic rank: This describes different levels of the Linnaean hierarchical classification. For example, species is one taxonomic rank; kingdom, phylum, and also course are various other ranks.

Taxonomy: the classification of living organisms, generally making use of the ordered device designed by Carolus Linnaeus.

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