Contents

Introduction
I. Overview of the Genetic Data
I.a. Molecular Differences between Various Extant Hominoids
I.a-1.) Chromosomal Difference between Genus Homo and Other Hominids
I.a-2.) Neoteny & Chromosome Reduction
I.a-3.) Genetic Neoteny, Delayed Development & Intelligence
I.b. Interfertility of Extant Populations
I.b-1.) Creating Humanzees
I.b-2.) Oliver, Koolakamba, & Other Alleged Hybrids
I.b-3.) Spermatozoic Cross-compatibility
I.b-4.) Chromosomal Differential & Interfertility
I.b-5.) Neoteny & Reduced Interfertility
I.c. The Molecular Clock
I.c-1.) The Hominin Concestor
I.c-2.) The Hominine Concestor
I.c-3.) The Hominid Concestor
I.c-4.) The Hominoid Concestor
I.d. Molecular Evidence of Messy Speciations
I.d-1.) Homo sapiens, Homo neanderthalensis, & the Denisovans
I.d-2.) Examples from the Hylobatids
I.d-3.) Hominina and Panina
I.d-4.) Hominini and Gorillini
I.d-5.) Pthirus gorillae and Pthirus pubis
I.e. Benefits of Hybridization
I.e-1.) Examples the Cercopithecoids
I.f. The Importance of Correlating Genetic Events with Fossil Record Events
II. Overview of the Hominoid Fossil Record
II.a. Miocene
II.b. Pliocene
II.c. Pleistocene
II.c-1.) Homo
III. Anatomical Curiosities, Anachronisms & Fringe Theories
III.a. The Enigmatic Australopithecines
III.a-1.) Allometric Inconsistencies
III.a-2.) Digitigrade Ancestry of Præanthropus
III.a-3.) Gorilla-like Traits in Paranthropus
III.b. Ancestral Bipedalism
III.b-1.) Australopithecus as an Ancestor of Panina
III.b-2.) Paranthropus as an Ancestor of Gorilla
III.b-3.) Incompatibilities with the Genetic Clock
III.b-4.) Earlier Examples of Bipedality
III.c. Regressive Similarity to Oreopithecus
III.c-1.) Oreopithecus & the Australopiths
III.c-2.) The Talus of Oreopithecus & Ardipithecus
III.c-3.) Sahelanthropus, Orrorin & the Australopiths
III.c-4.) Island Populations and the Aquatic Ape Theory
III.c-5.) Ancestral Bipedalism Revisited
IV. The Interbreeding Model
IV.a. Possible Anatomical Corroborations
IV.a-1.) Knuckle-walking as Evidence of Introgression
IV.a-2.) Effects among the Australopithecines
IV.b. Identifying Hybrid Populations
IV.b-1.) Genus Præanthropus
IV.b-2.) Genus Australopithecus
IV.b-3.) Genus Paranthopus
IV.b-4.) Genus Pan
V. Conclusions
V.a. Implications on Hominoid Taxonomy
V.a-1.) Reorganization of the Family Tree for “splitters”
V.a-2.) Doing Away with “Splitting”
V.a-3.) Compromise
V.a-4.) Discussion of Approaches
Works Cited

Background

I first began to ponder the question of ancient hybridization between the ancestors of humans and the chimpanzee-ancestors that existed contemporarily with them back in 1999.


D. J. Scott

Convergence or Introgression?

Interbreeding among the Ancestors of Humans, Chimpanzees, Gorillas, and Orangutans: Possible Anatomical Corroboration from Fossil & Extant Samples for Molecular Evidence of Gene Flow between Basal Members of Lineages Ancestral to Modern Hominoids with Regard to More Exacting Calibration of the Molecular Clock & Identification of the Functions of Genes Unique to Modern Humans, the Merging of Genera Pan and Gorilla into Genus Homo, the Australopiths as a Hybrid Population, and the Case for an Oreopithecus-like Human Ancestor
Copyright © 2016-2017 by Dustin Jon Scott
[Created: September 1st, 2016]
[Last Update: October 11th, 2017]


Introduction

Complex, “messy” speciation events, characterized by prolonged periods of gene flow via intermediate populations or direct hybridization, seem to be the rule rather than the exception for anthropoids. While other biological disciplines have in recent years revealed the importance of horizontal gene transfer in evolution, gene flow resulting from hybridization, or “diagonal gene transfer”, is quickly revealing itself as another important source of genetic diversity.

Interspecific and even intergeneric hybrids

Hybrid zone

Population hybrids

Hybrid species



I. Overview of the Genetic Data



I.a. Molecular Differences between Various Extant Hominoids

In the early 1990s, the genetic difference between humans and chimpanzees was considered to be around 1.6%, while the difference between chimpanzees and gorillas is 2.3% (Diamond, 1991, p.19), making humans and chimpanzees about 98.4% genetically identical, and tribe Hominini and tribe Gorillini about 97.7% genetically identical.



I.a-1.) Chromosomal Difference between Genus Homo and Other Hominids

Humans have 23 chromosome pairs, or 46 chromosomes.

All other apes have 24 chromosome pairs, or 48 chromosomes.

IJdo et al. (IJdo et al., 1991)
“Similarities in chromosome banding patterns and hybridization homologies between ape and human chromosomes suggest that human chromosome 2 arose out of the fusion of two ancestral ape chromosomes (1-3). Molecular data show evidence that this event must have occurred only a few million years ago (refs. 4 and 5 and the references therein). Although the precise nature of this putative fusion is unknown, cytogenetic data point to either a centromeric or telomeric fusion in the vicinity of region 2ql (1, 2, and 6). The observation that telomeric DNA is present in chromosomal band q13 suggests that telomeres, the extreme ends of chromosomes, may have been involved in this fusion (7, 8).” (IJdo et al., 1991)

According to the Biologos article, Denisovans, Humans, and the Chrosome 2 Fusion,

“[s]ince loss of a large amount of chromosomal material is almost always detrimental, we need an event that reduces chromosome number without losing information. One way for this to happen is for two chromosomes to fuse together and become one. Initially, this event would produce an individual with 47 chromosomes, where two different chromosomes get stuck together. Contrary to what is often assumed, this individual would be fertile and able to interbreed with the others in his or her population (who continue to have 48 chromosomes). In a small population, over time, two relatives who both have one copy of the fusion chromosome may mate and produce some progeny with two copies of the fused chromosome, or the first individuals with 46 chromosomes. Since either a 48-pair set or a 46-pair set is preferable for ease of cell division, this population will either eventually get rid of the fusion variant (the most likely outcome), or by chance will switch over completely to the “new” form, with everyone bearing 46 chromosome pairs [sic*].” (Venema, 2012)

* Note that Venema (2012) seems to be confusing chromosomes and chromosome pairs. Modern humans have 46 chromosomes, or 23 chromosome pairs — not 46 chromosome pairs. Likewise, modern apes have 24 chromosome pairs, or 48 chromosomes in total — not 48 chromosome pairs. In spoken discourse this could be dismissed as a slip of the tongue and probably amounts to little more than a typo.



I.a-2.) Neoteny & Chromosome Reduction

Neotony as a possible explanation for chromosomal differences between modern apes.

Genetic evidence points to the fusion of two ape chromosomes into Human Chromosome 2 occuring within the last few million years, the same time frame in which the ancestors of humans rapidly became increasingly morphologically neotenous.

It is not inconceivable that a reduction in chromosomal material could lead to morphological neoteny.

Autism-spectrum disorders and Human Chromosome 2

Autism-spectrum disorders and genetic neoteny

Syllogistic conclusion: genetic neoteny related to fusion of two ape chromosomes into Human Chromosome 2

Correlation between genetic/genotypic neoteny and morphological/phenotypic neoteny

Further syllogistic conclusion: Correlation between morphological phenotypic neoteny & fusion of two ape chromosomes into Human Chromosome 2



I.a-3.) Genetic Neoteny, Delayed Development & Intelligence

Correlation between genetically neotenous traits and delayed development associated with high intelligence.

Primates are genetically neotenous compared to other mammals, experience delayed brain development compared to other mammals, and have high intelligence by mammalian standards.

Apes are genetically neotenous compared to other primates, experience delayed brain development compared to other primate, and have high intelligence by primate standards.

Humans are genetically neotenous compared to other apes, experience delayed brain development compared to other apes, and have high intelligence by hominid standards.

(Yong 2009)



I.b. Interfertility of Extant Populations

Something needs to go here



I.b-1.) Creating Humanzees

All known attempts to hybridize modern humans with other modern apes have failed.

Experiments by Ilya Ivanovich Ivanov.



I.b-2.) Oliver, Koolakamba & Other Alleged Hybrids

Oliver was a captive chimpanzee popularly imagined to be “part human”.

Koolakamba is a supposed hybrid blah blah blah.



I.b-3.) Spermatozoic Cross-compatibility

Human spermatozoa can penetrate gibbon eggs.



I.b-4.) Chromosomal Differential & Interfertility

Chromosomal polymorphism:

“While not overly likely, this type of event is not especially rare in mammals, and we have observed this sort of thing happening within recorded human history in other species. Some mammalian species even maintain distinct populations in the wild with differing chromosome numbers due to fusions, and these populations retain the ability to interbreed.” (Venema, 2012)

Chromosome counts in Mus domesticus 22 to 40 pairs (Nachman et al., 1994), making the chromosomal differential between humans and other apes unlikely as the sole reason for reduced interfertility.

Since this is the most obvious genetic dissimilarity between humans and other apes, however, it seems likely that reduced interfertility at least coincided with human chromosome reduction in some way, and that the actual cause of our infertility with other apes is either a secondary effect of chromosome reduction, or that reduced interfertility was the cause of the genetic isolation that resulted in the universality of chromosome reduction in the human lineage.



I.b-5.) Neoteny & Reduced Interfertility

Stuff.



I.c. The Molecular Clock

Helped us to identify common ancestors, or “concestors”, the points at which separate lineages converge as we look backward through time. (Dawkins, 2004)



I.c-1.) The Hominin Concestor

The last common ancestor of both humans and chimpanzees.



I.c-2.) The Hominine Concestor

The last common ancestor of humans and gorillas.



I.c-3.) The Hominid Concestor

The last common ancestor of humans and orangutans.

http://news.nationalgeographic.com/news/2009/06/090623-humans-chimps-related.html



I.c-4.) The Hominoid Concestor

The last common ancestor of humans and gibbons.



I.d. Molecular Evidence of Messy Speciations

In the past, most speciation has been assumed to be allopatric (Futuyma & Mayer, 1980) and even the renowned Richard Dawkins has stated that species can’t diverge without being isolated (Dawkins, 2015), in spite of known cases of parapatric and sympatric modes of speciation, as well as hybrid speciation.

Molecular evidence for non-allopatric or “messy” speciations among cercopithecoids and several hominoids demonstrate that allopatric or “neat” speciation events may be the exception rather than the rule for large anthropoids.



I.d-1.) Homo sapiens, Homo neanderthalensis, & the Denisovans

(Ackermann et al., 2006)



I.d-2.) Examples from the Hylobatids

Species complex.



I.d-3.) Hominina and Panina

Blah blah blah

“Different chromosomes appear to have split at different times, possibly over as much as a 4-million-year period, indicating a long and drawn out speciation process with large-scale hybridization events between the two emerging lineages as late as 6.3 to 5.4 million years ago according to Patterson et al. (2006).[9] Wikipedia (Patterson et al., 2006)

Journalist Brian Handwerk of National Geographic News states

“[d]ifferent regions of the human and chimp genomes were found to have diverged at widely different times, and the two species' X chromosomes show a surprisingly recent divergence time.” (Handwerk, 2006)

Journalist Brian Handwerk of National Geographic News states

“[t]he [Patterson] study suggests that the human and chimp lineages initially split off from a single ape species about ten million years ago. Later, early chimps and early human ancestors may have begun interbreeding, creating hybrids—and complicating and prolonging the evolutionary separation of the two lineages,”(Handwerk, 2006)
and goes on to say,
“[t]he second and final split occurred some four million years after the first one, the report proposes.” (Handwerk, 2006)

However, Wakely (2008) questions whether this should be considered evidence of introgression, stating,

“[g]enetic data from two or more species provide information about the process of speciation. In their analysis of DNA from humans, chimpanzees, gorillas, orangutans and macaques (HCGOM), Patterson et al.1 suggest that the apparently short divergence time between humans and chimpanzees on the X chromosome is explained by a massive interspecific hybridization event in the ancestry of these two species. However, Patterson et al.1 do not statistically test their own null model of simple speciation before concluding that speciation was complex, and—even if the null model could be rejected—they do not consider other explanations of a short divergence time on the X chromosome. These include natural selection on the X chromosome in the common ancestor of humans and chimpanzees, changes in the ratio of male-to-female mutation rates over time, and less extreme versions of divergence with gene flow (see ref. 2, for example). I therefore believe that their claim of hybridization is unwarranted.”


I.d-4.) Hominini and Gorillini

A complex speciation event blah blah blah

(Scally & Dutheil et al., 2012)



I.d-5.) Pthirus gorillae and Pthirus pubis

The human pubic louse Pthirus pubis diverged from the gorilla louse Pthirus gorillae around 3 MYA.



I.e. Benefits of Hybridization



I.e-1.) Examples from the Cercopithecoids

(Ackermann et al., 2006)



I.f. The Importance of Correlating Genetic Events with Fossil Record Events

Regardless of whether apparently recent divergence times for certain genes result from introgression or intraspecific variation, determining which genetic changes correlate with certain anatomical changes can help us to better understand the functions of the genes in question.



II. Overview of the Hominoid Fossil Record



II.a. Oligocene (35 to 33 MYA)

[24-27 MYA] Proconsul hamiltoni


II.b. Miocene [23.03 to 5.333 MYA]

Original divergence of the human, chimpanzee, and gorilla lineages, about 13 MYA.

(Begun, 2010)



II.b-1.) Antiquanian [23.03 — 20.04 MYA]



II.b-2.) Burdigalian [20.04 — 15.97 MYA]



II.b-3.) Langhian [15.97 — 13.82 MYA]



II.b-4.) Serravallian [13.82 — 11.63 MYA]



II.b-5.) Tortonian [11.63 — 7.246 MYA]



II.b-6.) Messinian [7.246 — 5.333 MYA]



II.c. Pliocene [5.333 million to 2.58 MYA]

Interbreeding between the human and chimpanzee lineages ends possibly as recently as 4 MYA.

(Haile-Selassie et al., 2017)



II.c-1.) Zanclean [5.333 — 3.6 MYA]



II.c-2.) Piacenzian [3.6 — 2.58 MYA]



II.d. Pleistocene

2,588,000 to 11,700 years ago.



II.d-1.) Gelasian [2.58 — 1.8 MYA]



II.d-2.) Calabrian [1.8 MYA — 781 KYA]



II.d-3.) Ionian [781 KYA — 126 KYA]



II.d-4.) Tarantian [126 KYA — 11.7 KYA]



II.d. Holocene



III. Anatomical Curiosities, Anachronisms, and Fringe Theories



III.a. The Enigmatic Australopithecines



III.a-1.) Allometric Inconsistencies

Australopithecus anamensis

Australopithecus afarensis

Type specimen AL 288-1 or “Lucy” (Johanson, 1976) had a humerofemoral index of 85.1, “intermediate” when compared with Homo sapiens and the other Great Apes. (Jungers, 1982)

A study of the limb proportions of the Australopithecine

“In contrast, A. afarensis and anamensis more closely approximate a human pattern of forelimb to hindlimb joint size. This is an unanticipated complication in our understanding of early human evolution. In general, craniodental morphology tracks time in species of Australopithecus: A. anamensis (3.5-4.1 Ma) is the most primitive with a strongly sloping symphysis, large canine roots, etc., A. afarensis (3.0-3.6 Ma) is less primitive (Berger & McHenry, 1998)

Australopithecus africanus

“New discoveries of A. africanus fossils from Member 4 Sterkfontein reveal a body form quite unlike earlier Australopithecus species. The new adult material consists of over 48 fore- and hindlimb specimens and includes an associated partial skeleton, Stw 431. The forelimbs are relatively large: the average size of their joints corresponds to a modern human with body mass of 53 kg. The hindlimbs are much smaller with an average size matching a modern human of only 33 kg. Analyses of the Stw 431 partial skeleton confirm these results.” (Berger & McHenry, 1998)
A. africanus (2.6-3.0 Ma) shares many derived characteristics with early Homo (e.g., expanded brain, reduced canine, bicuspid lower third premolar, reduced prognathism, greater flexion of the cranial base, deeper TMJ). The new postcranial material, however, reveals an apparently primitive morphology of relatively large forelimb and small hindlimb joints resembling more the pongid than the human pattern. More pongid-like proportions are also present in the two known associated partial skeletons of H. habilis (OH 62 and KNM-ER 3735). This may imply either (1) that A. africanus and H. habilis evolved craniodental characters in parallel with the lineage leading to later Homo, or (2) that fore- to hindlimb proportions of A. afarensis (and perhaps A. anamensis) evolved independent of the lineage leading to Homo and does not imply a close phylogenetic link with Homo.” (Berger & McHenry, 1998)

Australopithecus habilis (Homo habilis)

OH 62Homo habilis?

“Although the difference in humerofemoral proportions between OH 62 and AL 288-1 does not exceed variation in the extant samples, it is rare. When humerofemoral midshaft circumferences are compared, the difference between OH 62 and AL 288-1 is fairly common in extant species. This, in combination with error associated with the limb lengths estimates, suggests that it may be premature to consider H. (or Australopithecus) habilis as having more apelike limb proportions than those in A. afarensis.”
J Hum Evol. 2002 Oct;43(4):529-48.
Early hominin limb proportions.
Richmond BG1, Aiello LC, Wood BA.
(Richmond et al., 2002)
“The humerus and femur of the fossil hominid OH 62 are badly damaged and their lengths are not directly measurable (Johanson et al., 1987). Nevertheless, using relatively intact reference materials from another early hominid, AL 288-1, Johanson et al. (1987) reconstructed the bones to estimate the humerofemoral index, which falls well above the range for modern Homo, above the estimate for AL 288-1, and within the range for Pan paniscus. The reconstruction of missing bone by the method originally employed for OH 62 is broadly reproducible in a representative modern sample of Homo, making possible the estimation of an associated error term intrinsic to this method. Using the approximate variance of the ratio mean (Kish, 1965), shown here to be a good estimator of the sample variance of the humerofemoral index, the analysis of this modern sample extrapolated to other living hominoids gives quite acceptable results. Applied to OH 62, it suggests an error term associated with the estimated humerofemoral index so substantial that it is only possible to situate the index somewhere between the distributions for Homo and Gorilla, and quite possibly not above the index for AL 288-1. On the other hand, the predicted distribution for the humerofemoral index of AL 288-1 is more securely placed between the distributions for Homo and Pan paniscus.”
Am J Phys Anthropol. 1990 Sep;83(1):25-33.
Deconstructing reconstruction: the OH 62 humerofemoral index.
Korey KA1.
(Korey, 1990)

Bouri skeleton, BOU-VP 12/1

“The humerofemoral index of BOU-VP 12/1 differs significantly from both OH 62 and AL 288-1, but not from KNM-WT 15000. Published length estimates, if correct, suggest that the relative forearm length of BOU-VP 12/1 is unique among hominins, exceeding those of the African apes and resembling the proportions in Pongo.”
J Hum Evol. 2002 Oct;43(4):529-48.
Early hominin limb proportions.
Richmond BG1, Aiello LC, Wood BA.
(Richmond et al., 2002)

According to Green et al., Homo habilis may have had either apelike or humanlike limb proportions (2007), or, as is more likely the case, displayed a range that was similar to H. sapiens and Pr./Au. afarensis on the one end and similar to Au. africanus on the other.

OH 34 – H. erectus or Par. boisei?

(Green et al., 2007)(Berger, 1998)

Australopithecus garhi

Homo habilis, which some researchers, including Richard Leakey, have suggested would be better reclassified as Australopithecus habilis.


III.a-2.) Digitigrade Ancestry of Præanthropus

In a letter to Nature, entitled Evidence that humans evolved from a knuckle-walking ancestor, Brian G. Richmond and David S. Strait of George Washington University argue that analysis of the carpal morphology of Pr./Au. anamensis (KNM-ER 20419) and Pr./Au. afarensius (AL 288-1) demonstrate retained specializations associated with knuckle-walking, indicating a digitigrade quadruped ancestor for Præanthropus. (Richmond & Strait, 2000)

Retained from what? This is interesting because Ardipithecus, which lived closer to the date of divergence for Hominina and Panina, was not a knuckle-walker. Ardipithecus was most likely an arboreally plantigrade quadruped and a terrestrial plantigrade biped, making it unlikely to have been ancestral to a terrestrially digitigrade quadruped (like modern chimpanzees) that later spawned arboreally suspensory, terrestrial plantigrade bipeds (like the Australopiths). How and why evidence of knuckle-walking adaptations would have been retained in terrestrial bipeds who descended from terrestrial bipeds lacking such adaptations is currently somewhat of a mystery, to which molecular evidence of an interbreeding event between the ancestors of Panina and the ancestors of Hominina as late as 4 MYA provides a valuable clue.



III.a-3.) Gorilla-like Traits in Paranthropus



III.b. Ancestral Bipedalism

Also known as “Ancestral Bipedalism”,

The main consequence of this hypothesis is the placement of A. afarensis in a position ancestral to African apes. An argument in support of this alternative paradigm is formulated concerning the evolution of knuckle-walking in African apes from ancestors whose bipedalism was already well developed. Published data are cited, particularly concerning the structure of the wrist, which accommodate poorly the evolution of African apes from palmigrad-walking or brachiating ancestors resembling Proconsul africanus or Pongo. These arguments suggest that an alternative paradigm of hominoid evolution placing A. afarensis ancestral to Homo, Gorilla, and Pan warrants further consideration.

(Edelstein, 1987)

S. J. Edelstein, An Alternative Paradigm for Hominoid Evolution. HUMAN EVOLUTION Vol. 2 - N. 2 (169-174) - 1987
<http://www.unige.ch/sciences/biochimie/Edelstein/Edelstein%201987%20Alternative%20paradigm.pdf>

An alternate version of this model would make genus Australopithecus (in its most inclusive sense, roughly corresponding to subtribe Australopithecina, including both Praeanthropus and Paranthropus) ancestral to Homo, Pan, and Gorilla, whith the gracile Australopithecines (genus Australopithecus in its more commonly understood sense) ancestral to Homo and Pan, and the robust Australopithecines (sometimes separated into their own genus, Paranthropus) ancestral to genus Gorilla, based on numberous morphological similarities otherwise interpreted as homoplasy (convergent or parallel evolution).



III.b-1.) Australopithecus as an Ancestor of Panina

One of the main problems with this involves the earliest gracile Australopithecines showing evidence in their carpals of characteristics retained from a knuckle-walking ancestor. This would mean that chimpanzees evolved digitigrade quadrupedality independently of the gorilla lineage from a non-knuckle-walking biped (Australopithecus) who in turn evolved from an unrepresented digitigrade ancestor, who in turn evolved from a non-knuckle-walking bipedal ancestor (Ardipithecus).



III.b-2.) Paranthropus as an Ancestor of Gorilla



III.b-3.) Incompatibilities with the Genetic Clock



III.b-4.) Earlier Examples of Bipedality



III.c. Regressive similarity to Oreopithecus



III.c-1.) Oreopithecus & the Australopiths



III.c-2.) The Hallux of Oreopithecus & Ardipithecus



III.c-3.) Sahelanthropus, Orrorin & the Australopiths



III.c-4.) Island populations and the Aquatic Ape Theory

Species can’t diverge without being isolated. https://www.youtube.com/watch?v=1gjUXT99gC0 Is Evolution Predictable?

(Niemtiz, 2010)



III.c-5.) Ancestral Bipedalism Revisited



IV. The Interbreeding Model

First it is important to distinguish between an interbreeding model and a hybridization model. While use of the term “hybridization” implies that introgressions occurred subsequent to divergence into (mostly) genetically isolated lineages representing separate, distinct species, an interbreeding model of hominid evolution merely requires what Wakely refers to as “less extreme versions of divergence with gene flow” (2008) which could be thought to include geneflow through intraspecific hybrid populations – in other words, that genetic isolation occurred gradually over a long period of time. So while an interbreeding model of hominid evolution potentially subsumes any and all interspecific hybridization hypotheses, it does not definitively include them, giving no preference to post-speciation introgressions (interspecific hybridization with backcrossing) over gradual divergence with localized intraspecific hybridization events and extensive “intragression”, and therefore allows for the possibility that the individuals who interbred existed as part of a more diverse species comprising a continuum of interfertility.



IV.a. Possible Anatomical Corroborations

Within the framework of the interbreeding model, we can revisit the anatomical curiosities borne out in the fossil record in a new context.



IV.a-1.) Knuckle-walking as Evidence of Introgression

About 4.2 MYA genus Præanthropus appears, bearing, as noted earlier, carpal evidence of retained knuckle-walking adaptations absent in their probable immediate ancestor, Ardipithecus. This coincides with low-end estimates for an interbreeding event between the ancestors of humans and chimpanzees roughly 7-4 MYA, approximately one million years after their initial divergence from a common ancestor 8-5 MYA according to older estimates using the genetic clock, but more recent estimates for the last divergence from a common ancestor around 5.4 MYA would antedate the earliest evidence for Præanthropus in the fossil record by about 1.2 MY.

The appearance of retained knuckle-walking adaptations in Præanthropus is problematic if the Australopiths descended from an Ardipithecus-like bipedal ancestor that did not use its knuckles to support itself when moving quadrupedally, which had diverged allopatrically from branches of the hominid family tree which eventually produced knuckle-walkers. This speaks strongly in favor of the evidence for retained knuckle-walking adaptations in Præanthropus indicating descent from a time when genetic isolation of modern lineages was still incomplete, with a hybridization event between Hominina and Panina (or the immediate ancestors thereof) subsequent both to their initial divergence from the first hominin concestor 10 MYA and to the adoption of a knuckle-walking mode of locomotion by at least some ancestors in the lineage leading to the extant subtribe Panina prior to their last divergence as late as 4 MYA.

Whether the appearance of knuckle-walking both in tribe Gorillini and in subtribe Panina of tribe Hominini, while the hominin concestor (and logically therefore the hominine concestor) is unlikely to have been a knuckle-walker, is the result of convergent evolution (“linear” homoplasy) or an example of introgressions from tribe Gorillini into Hominini (“horizontal” homoplasy) is unclear, however, “[i]n 30% of the genome, gorilla is closer to human or chimpanzee than the latter are to each other,” (Scally & Dutheil et al., 2012), meaning that chimpanzees have genetic material in common with gorillas which humans do not possess. While Scally & Dutheil et al. attribute this to separate selection forces in the human and chimpanzee lineages, considering the genetic differences between even extant populations of humans, chimpanzees, and gorillas are more minute than sometimes found between members of the same species (Diamond, 1991), introgression cannot be ruled out as an explanation.

Thus, it’s probable that Præanthropus displays evidence of retained knuckle-walking adaptations in its carpals due to introgression from the chimpanzee lineage, which had in turn acquired its digitigrade form of quadrupedality via introgression from the gorilla lineage, or else Præanthropus and the chimpanzee lineage both experienced introgression through (an) unattested Hominini-Gorillini hybrid population(s), or some combination thereof. It may be that the chimpanzee lineage is the hybrid population that Præanthropus experienced backcrossing from, or that the human lineage is unattested from this time period and that both Præanthropus and the chimpanzee lineage are hybrid populations. (For more discussion on this, see Identifying Hybrid Populations.)



IV.a-2.) Effects among the Australopithecines

Concerning the aforementioned inconsistencies in Australopithecine limb allometry,

“When applied to the fossil samples, upper:lower limb-size proportions in A. afarensis are similar to those of humans (p = 0.878) and are significantly different from all great ape proportions (p = 0.034), while Australopithecus africanus is more similar to the apes (p = 0.180) and significantly different from humans and A. afarensis (p = 0.031). These results strongly support the hypothesis that A. africanus possessed more apelike limb-size proportions than A. afarensis, suggesting that A. africanus either evolved from a more postcranially primitive ancestor than A. afarensis or that the more apelike limb-size proportions of A. africanus were secondarily derived from an A. afarensis-like ancestor.” (Green et al. 2007, Abstract)

Given the evidence for interbreeding events between the human and chimpanzee lineages as recently as 4 MYA, shortly after the appearance in the fossil record of Au./Pr. anamensis, it is entirely possible that A. africanus did not simplistically “evolve from” a postcranially more primitive ancestor but that its “primitive” limb proportions, rather than being secondarily derived, were inherited from a postcranially A. afarensis-like ancestor that experienced introgression from the chimpanzee lineage via backcrossing from a hybrid population facilitating gene flow.



IV.b. Identifying Hybrid Populations



IV.b-1.) Genus Præanthropus



IV.b-2.) Genus Australopithecus



IV.b-3.) Genus Paranthropus



IV.b-4.) Genus Pan



IV.c.) Introgressions



IV.c-1.) First Introgression Period


Early Terrestrial Quadrupedality?
Kenyapithecina?

×


Early Terrestrial Bipedality?
Graecopithecina?

Primitive Bipeds & Quadrupeds
Dryopithecina?

Primitive Bipeds & Quadrupeds
Sivapithecina?


IV.c-1.) Second Introgression Period



IV.c-2A.) Occidental Introgression

Quadrupedality & Bipedality
Dryopithecina?

×


Quadrupedality
Kenyapithecina?

Bipedality
Reduced Prognathism
Oreopithecina?

Quadrupedality
Pronounced Prognathism?
Chororapithecina?


IV.c-2B.) Oriental Introgression


IV.c-3.) Third Introgression


Primitive Bipeds & Quadrupeds
Dryopithecina?
x
Primitive Bipeds & Quadrupeds
Sivapithecina?

Bipeds
Oreopithecina?

Quadrupeds
Chororapithecina?

Quadrupeds
Pongo?

Bipeds
Gigantopithecina?


IV.c-3.) Third Introgression


[HCA]
(Human-Chimpanzee Ancestor)

Bipedality
Smooth Crania
Slight Brachyganthism
Pronounced Hallucial Abduction
Oreopithecina
x
[GA]
(Gorilla Ancestor)

Quadrupedality
Robust Crania?
Prognathism?
Reduced Hallucial Abduction?
Chororapithecina


Bipedality
Gracile Crania
Brachygnathism
Pronounced Hallucial Adduction
Homo


Bipedality
Gracile Crania
Prognathism
Intermediate Hallucial Adduction
Praeanthropus


Bipedality
Robust Crania
Brachygnathism
Pronounced Hallucial Adduction?
Paranthropus


Quadrupedality
Gracile Crania
Prognathism
Intermediate Hallucial Abduction
Pan


Quadrupedality
Robust Crania
Prognathism
Reduced Hallucial Abduction
Gorilla


IV.c-3B.) Third Introgression Period


Bipeds
Smooth Crania
Abducted Hallux
Oreopithecina
x

Quadrupeds
Robust Crania?
Slightly Adducted Hallux?
Chororapithecina


Bipeds
Smooth Crania
Intermediately Adducted Hallux
Australopithecina


Quadrupeds
Prognathic
Smooth Crania
Abducted Hallux
Panina


Quadrupeds
Prognathic
Robust Crania
Less Abducted Hallux
Gorillina


IV.c-3A.) Third Introgression Period: Phase I


Bipeds
Smooth Crania
Abducted Hallux
Oreopithecina
x

Quadrupeds
Robust Crania?
Slightly Adducted Hallux?
Chororapithecina


Bipeds
Smooth Crania
Intermediately Adducted Hallux
Australopithecina


Quadrupeds
Prognathic
Smooth Crania
Abducted Hallux
Panina


Quadrupeds
Prognathic
Robust Crania
Less Abducted Hallux
Gorillina


V. Conclusions

Of the genus Homo, genus Pan, genus Gorilla, Scally & Dutheil et al. write “[i]t is notable that species within at least three of these genera continued to exchange genetic material long after separation.” (2012) Thus, the expectation of single-point concestors, with each lineage diverging instantaneously and irrevocably into fully-isolated lineages, is wishful thinking borne of a desire for taxonomic convenience.



V.a. Implications on Hominoid Taxonomy



V.a-1. Reorganization of the Family Tree for “Splitters”

Superfamily Hominoidea
Family Proconsulidae
Hominoid concestor (human-gibbon MRCA) –
Family Hylobatidae
Family Hominidae
Subfamily Kenyapithecinae – simultaneously the palæosubfamily to both Homininae and Ponginae, comprising organisms that existed at a time before the ancestors of the extant forms of Homininae and Ponginae could have justifiably been separable into distinct subfamilies.
Tribe Kenyapithecini
The geographical distribution of this group was pan-Eurafrican, existing both north and south of what is now the Mediterranean Sea, with the subfamily's namesake genus, Kenyapithecus, likely being one of the southernmost examples.
Hominid concestor (human-orangutan MRCA) –
Subtribe Græcopithecina (my classification)–
Genus Ouranopithecus
Species Ouranopithecus macedoniensis
Genus Pierolapithecus
Species Pierolapithecus catalaunicus
Genus Græcopithecus
Species Græcopithecus freybergi
Subtribe Kenyapithecina
Genus Kenyapithecus
Species Kenyapithecus wickeri [14 MYA]–
14 million years ago
Knuckle-walking mode of semi-terrestrial locomotion (McCrossin et al. 1998, p. 353-396)
Tribes Dryopithicini and Sivapithecini – introgression
“Since few great ape fossils have been found in Africa so far, ‘some scientists have forcefully suggested that the ancestors of African apes and humans must have emerged in Eurasia,’ said study senior author Gen Suwa, a palæoanthropologist at the University of Tokyo.” (Charles Q. Choi, LiveScience on February 12, 2016)
Subfamily Ponginae
Tribe Sivapithecini
Subtribe(s) N/A –
Genus Ankarapithecus
Genus Sivapithecus
Genus Gigantopithecus
Tribe Lufengpithecini
Tribe Pongini
Subtribe(s) N/A –
Genus Khoratpithecus
Species Khoratpithecus chiangmuanensis
Species Khoratpithecus piriyai
Species Khoratpithecus ayeyarwadyensi
Genus Pongo
Subfamily Homininae – one of two extant chronosubfamilies to the Kenyapithecinae (the other being the Ponginae).
Tribe Dryopithicini – simultaneously the palæotribe to both Gorillini and Hominini, and may itself be a chronotribe of Kenyapithecini, resulting from hybridization between the Graecopithecina and the Kenyapithecina.
Hominine concestor (human-gorilla near-MRCA) – the near-to-last common ancestor of Homo and Gorilla, representing their first initial split into not-yet-completely-reproductively-isolated groups. Descendants of this near-to-last common ancestor would eventually become separable into two subtribes: Chororapithecina, the probable palæosubtribe of Gorillina, and Oreopithecina, a palæosubtribe to both Hominina and Panina. It is likely the Chororapithecina and Oreopithecina continued occasionally to either hybridize directly or otherwise benefit from indirect gene flow through intermediate populations.
Subtribe Dryopithecina
Genus Dryopithecus
Genus Rudapithecus
Genus Samburupithecus
Subtribe ??? –
Genus Nakalipithecus
Genus Anoiapithecus
Subtribe Chororapithecina (my classification) – with Dryopithecini being a palæotribe of both Hominini and Gorillini, having existed at a time when it was not yet meaningful to distinguish basal members of Hominini and Gorillini at the tribe-level, this subtribe would be shared by the extant tribe Gorillini and its palæotribe Dryopithecini, but not by palæotribe Dryopithecini's other extant chronotribe Hominini. Chororapithecina may have begun as a hybrid population of the Graecopithecina with Kenyapithecina.
Genus Chororapithecus (Suwa et al., 2007) –
Species Chororapithecus abyssinicus – Also read: (Shigehiro et al., 2015)
Subtribe Oreopithecina (my classification) – with Dryopithicini being a palæotribe concestral to both Hominini and Gorillini, having existed at a time when it was not yet meaningful to distinguish basal members of Hominini and Gorillini at the tribe-level, this subtribe would be shared by the stem-hominin palæotribe Dryopithecini and its later chronotribe Hominini, but not by palæotribe Dryopithecini's other extant chronotribe Gorillini, and would be a palæosubtribe to both extant subtribe Hominina and extant subtribe Panina, having existed at a time when it was not yet meaningful to distinguish basal members of Hominina and Panina at the subtribe-level.
Genus Oreopithecus (Gervais, Paul 1872) –
Hypothetical mainland Oreopithecus (or similar) species –
Genus Orrorin
Species Orrorin tugenensis
Genus Sahelanthropus
Species Sahelanthropus tchadensis
Genus Ardipithecus
Species Ardipithecus ramidus
Species Ardipithecus kadabba
Tribe Gorillini – one of two now-distinct modern chronotribes to palæotribe Dryopithecini, tribe Gorillini would include the modern subtribe Gorillina and its probable palæosubtribe Chororapithecina, but would not include Dryopithecini’s other subtribe, Oreopithecina, which was instead the palæosubtribe to Hominina and Panina.
Subtribe Chororapithecina (my classification) – with Dryopithecini being a palæotribe concestral to both Hominini and Gorillini, having existed at a time before it was meaningful to distinguish Hominini from Gorillini at the tribe-level, this subtribe would be shared by both the tribe Dryopithecini and its later chronotribe Gorillini, but not by Dryopithecini's other chronotribe Hominini, and would be a probable palæosubtribe to Gorillina (also my classification).
Subtribe Gorillina (my classification)
Genus Gorilla
Tribe Hominini – one of two now-distinct modern chronotribes to palæotribe Dryopithecini, tribe Hominini includes the modern subtribes Hominina and Panina, as well as their concestral palæsubtribe Oreopithecina and the now-defunct subtribe Australopithecina.
Subtribe Oreopithecina (my classification) – having existed at a time before it was meaningful to distinguish basal members of the Hominina and Panina at the subtribe-level, this subtribe would be shared by both the extant tribe Hominini and its earlier chronotribe Dryopithecini, and would represent a palæosubtribe concestral to both subtribes Hominina and Panina.
Early Oreopithecins –
Hominin concestor (human-chimpanzee near-MRCA) – a progenitor that was the near-to-last common ancestor of Homo and Pan, excepting for occasional hybridization events subsequent to a “main split” into two distinct but initially non-reproductively-isolated lineages, the Hominina and Panina, perhaps best viewed at first as non-distinct yet artificially distinguishable sides of a “ring species”-like interfertility continuum, possibly involving clines.
Later Oreopithecins / early Hominina
Subtribe Australopithecina – a now-defunct palæosubtribe to extant subtribe Hominina.
Genus Ardipithecus
Genus Kenyanthropus
Species Kenyanthropus platyops
Genus Prænthropus
Species Prænthropus anamensis
Species Prænthropus afarensis
Species Prænthropus bahrelghazali
Species Prænthropus garhi
Genus Australopithecus
Species Australopithecus africanis
Species Australopithecus deyiremeda
Species Australopithecus garhi
Species Australopithecus sediba
Genus Paranthropus
Species Paranthropus robustus
Species Paranthropus boisei
Early genus Homo
Species Homo habilis
Species Homo rudolfensis
Subtribe Panina – a modern subtribe that includes descendants of its palæosubtribe, the Oreopithecini, that are more closely related to modern chimpanzees than to modern humans. Thus far, the chimpanzees and bonobos are the only known members, fossil or extant, of this subtribe.
Genus Pan – In a letter to Nature magazine, entitled First fossil chimpanzee, Sally McBrearty of the Department of Anthropology of the University of Connecticut and Nina G. Jablonski of the Department of Anthropology of the California Academy of Sciences state, “There are thousands of fossils of hominins, but no fossil chimpanzee has yet been reported. The chimpanzee (Pan) is the closest living relative to humans1. Chimpanzee populations today are confined to wooded West and central Africa, whereas most hominin fossil sites occur in the semi-arid East African Rift Valley. This situation has fuelled [sic] speculation regarding causes for the divergence of the human and chimpanzee lineages five to eight million years ago. Some investigators have invoked a shift from wooded to savannah vegetation in East Africa, driven by climate change, to explain the apparent separation between chimpanzee and human ancestral populations and the origin of the unique hominin locomotor adaptation, bipedalism2, 3, 4, 5. The Rift Valley itself functions as an obstacle to chimpanzee occupation in some scenarios6. Here we report the first fossil chimpanzee. These fossils, from the Kapthurin Formation, Kenya, show that representatives of Pan were present in the East African Rift Valley during the Middle Pleistocene, where they were contemporary with an extinct species of Homo. Habitats suitable for both hominins and chimpanzees were clearly present there during this period, and the Rift Valley did not present an impenetrable barrier to chimpanzee occupation.” (McBrearty & Jablonski, 2005)
Species Pan troglodytes
Subspecies Pan troglodytes troglodytes
Species Pan paniscus
Subtribe Hominina – a modern subtribe that includes descendants of Hominina and Panina's shared palæosubtribe, the Oreopithecini, that are more closely related to modern humans than to modern chimpanzees and bonobos. This subtribe could be liberally defined to include stem hominins which “leaned toward the human side” of a “ring-species”-like continuum of interfertility that once existed facilitating gene flow between what were initially only semi-genetically-isolated lineages or groups, thus including creatures still capable of interbreeding with the ancestors of modern chimpanzees and bonobos either directly or via intermediate populations which still existed, or could be conservatively defined to only include creatures which were fully reproductively isolated from the ancestors of modern chimpanzees and bonobos. Such a conservative definition of Hominina becomes problematic, however, if genus Paranthropus should somehow be demonstrated to have been reproductively isolated from their contemporary ancestors of extant subtribe Panina, as the common ancestor of genus Homo and genus Paranthropus likely would not have been reproductively isolated from the their contemporary ancestors of Panina, thus making subtribe Homina a polyphyletic grouping.
Early Hominina- / late Oreopithecina – pr
Later Hominina
Genus Meganthropus
Genus Paranthropus
Genus Homo
Species Homo habilis
Species Homo naledi
Species Homo rudolfensis
Species Homo ergaster
Species Homo erectus
Subspecies Homo erectus erectus
Subspecies Homo erectus pekinensis
Subspecies Homo erectus yuanmouensis
Subspecies Homo erectus tautavelensis
Subspecies Homo erectus soloensis
Subspecies Homo erectus lantianensis
Subspecies Homo erectus nankinensis
Subspecies Homo erectus bilzingslebenensis
Subspecies Homo erectus palaeojavanicus
Subspecies Homo erectus georgicus
Species Homo palaeojavanicus
Species Homo floresiensis
Species Homo hiedelbergensis
Subspecies Homo heidelbergensis antecessor
Subspecies Homo heidelbergensis heidelbergensis
Subspecies Homo heidelbergensis rhodesiensis
Species Homo sapiens
Subspecies Homo sapiens antecessor
Subspecies Homo sapiens idaltu
Subspecies Homo sapiens heidelbergensis
Subspecies Homo sapiens rhodesiensis
Subspecies Homo sapiens neanderthalensis
Subspecies Homo sapiens sapiens


V.a-2.) Doing Away with “Splitting”

Subfamily Homininae → genus Homo
• Genus Gorilla → species H. gorilla
• Genus Pan → species H. troglodytes
• Genus Homo → species Homo sapiens, Homo africanus, Homo afarensis

Given that the difference between humans and chimpanzees is about 1.6%, and the difference between either of these and gorillas is about 2.3%, smaller than the difference sometimes seen between varieties within the same species, such as the various subspecies of red-eyed vireo (Vireo griseus) and white-eyed vireo (Vireo olivaceus), which can differ by up to 2.9% (Diamond, 1991, p.19) it is not at all unreasonable to place humans, chimpanzees, and gorillas in the same genus, merging Gorilla and Pan into genus Homo. This would remove the need for subfamily Homininae to be subdivided into tribes Hominini and Gorillini, since, under this scheme, subfamily Homininae would include only a single genus.

Genus Gorilla → species Homo gorilla
• Species Go. gorilla → species H. g. gorilla
• Species Go. graueri → subspecies H. g. graueri

A possible descendant of H. abyssinicus, Homo gorilla possesses derived traits in common with a number of other species in its genus, including humerofemoral proportions and digitigrade forelimbs like that of H. troglodytes and sagittal crests like H. robustus and H. ramidus, which may have arisen through direction hybridization with or indirect gene flow from either H. gorilla or its probable predecessor H. abyssinicus, and a less divergent hallux than what is typically seen in primates, possibly resulting from hybridization with or indirect gene flow from H. africanus.

Genus Pan → species Homo troglodytes
• Species P. troglodytes → subspecies H. tr. troglodytes
• Species P. paniscus → subspecies H. tr. paniscus

Genus Australopithecus → species Homo africanus, H. robustus, H. afarensis
• Species Au./Pr. anamensis → subspecies H. afr./afa. anamensis
• Species Au. afarensis / Pr. africanus → subspecies H. afr./afa afarensis
• Species Au./K. platyops → subspecies H. afr./afa. platyops/afarensis
• Species Au. africanus → subspecies H. afr. africanus
• Species Au./Pr. bahrelghazali → subspecies H. afr./afa. bahrelghazali
• Species Au./Pr. garhi → subspecies H. afr./afa. garhi
• Species Au. sediba → subspecies H. afr. sediba
• Species Au. antiquus → subspecies H. afr./afa. antiquus
• Species Au. habilis → subspecies H. afr. habilis
• Species Au./Par. aethiopicus → subspecies H. ro. aethiopicus
• Species Au. deyiremeda → subspecies H. afr./afa. deyiremeda
• Species Au./Par. robustus → subspecies H. ro. robustus
• Species Au./Par. boisei → subspecies H. ro. boisei
• Species Au./Par. walkeri → subspecies H. ro. walkeri

Genus Præanthropus → species Homo tugenensis, H. africanus, H. afarensis
• Species Pr./Orr. tugenensis → (sub)species H. (afa./afr.) tugenensis
• Species Pr./Au. anamensis → subspecies H. afr./afa. anamensis
• Species Pr./Au. africanus → subspecies H. afr./afa. afarensis
• Species Pr./Au. bahrelghazali → subspecies H. afr./afa. bahrelghazali
• Species Pr./Au. garhi → subspecies H. afr./afa. garhi

Genus Kenyanthropus → species Homo africanus, H. afarensis
• Species K./Au. platyops → subspecies H. afr./afa. platyops/afarensis

Genus Paranthropus → species Homo robustus
• Species Par./Au. aethiopicus → subspecies H. ro. aethiopicus
• Species Par./Au. robustus → subspecies H. ro. robustus
• Species Par./Au. boisei → subspecies H. ro. boisei
• Species Par./Au. walkeri → subspecies H. ro. walkeri

Genus Homo → species Homo sapiens, H. africanus, H. afarensis
• Species H. neanderthalensis → subspecies H. s. neanderthalensis
• Species H. heidelbergensis → subspecies H. s. heidelbergensis
• Species H. antecessor → subspecies H. s. antecessor
• Species H. floresiensis → subspecies H. s. floresiensis
• Species H. cepranensis → subspecies H. s. cepranensis
• Species H. erectus → various subspecies:
• Subspecies H. e. erectus → subspecies H. s. erectus
• Subspecies H. e. pekinensis → subspecies H. s. pekinensis
• Subspecies H. e. yuanmouensis → subspecies H. s. yuanmouensis
• Subspecies H. e. tautavelensis → subspecies H. s. tautavelensis
• Subspecies H. e. soloensis → subspecies H. s. soloensis
• Subspecies H. e. lantianensis → subspecies H. s. lantianensis
• Subspecies H. e. nankinensis → subspecies H. s. nankinensis
• Subspecies H. e. bilzingslebenensis → subspecies H. s. bilzingslebenensis
• Subspecies H. e. palaeojavanicus → subspecies H. afr./ro./s. palaeojavanicus
• Subspecies H. e. georgicus → subspecies H. afr./s. georgicus
• Species H. ergaster → subspecies H. s. ergaster
• Species H. rudolfensis → subspecies H. afr. rudolfensis
• Species H. naledi → subspecies H. afr. naledi
• Species H. habilis → subspecies H. afr. habilis
• Species H. antiquus → subspecies H. afr./afa. antiquus

Habilines like Homo habilis, Homo antiquus, and Homo rudolfensis might be better placed in species Homo africanus by virtue of their apelike limb-proportions. Their humerofemoral length proportions may have become more humanlike overtime due to backcrossing with Homo afarensis. Other early members of genus Homo such as Homo rudolfensis would necessarily blah blah blah.

Genus Meganthropus → species Homo sapiens, Homo africanus, Homo robustus

Genus Ardipithecus → species Homo ramidus, H. bamboli, H. fontani
• Species Ar. ramidus → subspecies H. ra./f./b. ramidus
• Species Ar. kadabba → subspecies H. ra. kadabba / H. f./b. ramidus

Genus Orrorin → species Homo tugenensis, H. afarensis, H. africanus
• Species Orr./Pr. tugenensis → (sub)species H. (afa./afr.) tugenensis

Genus Sahelanthropus → species Homo tchadensis

Genus Oreopithecus → species Homo bamboli, H. fontani
• Species Ore. bamboli → subspecies H. f./b. bamboli

Genus Chororapithecus → species Homo abyssinicus, H. fontani
• Species C. abyssinicus → (sub)species H. (f.) abyssinicus

Genus Samburupithecus → species Homo kiptalami, Homo fontani
• Species Sam. kiptalami → (sub)species H. (f.) kiptalami

Genus Dryopithecus → species Homo fontani, H. wuduensis, H. laietanus, H. crusafonti
• Species D. fontani → (sub)species H. (f.) fontani
• Species D. wuduensis → (sub)species H. (f.) wuduensis
• Species D. laietanus → (sub)species H. (f.) laietanus
• Species D. crusafonti → (sub)species H. (f.) crusafonti

Genus Anoiapithecus → species Homo brevirostris or H. fontani
• Species An. brevirostris → (sub)species H. (f.) brevirostris

Genus Nakalipithecus → species Homo nakayamai or H. fontani
• Species N. nakayamai → (sub)species H. (f.) nakayamai

Subfamily Ponginae → genus Pongo
• Genus Pongo → species Po. pygmæus
• Genus Sivapithecus → species Po. indicus
• Genus Gigantopithecus → species Po. blacki

Genus Sivapithecus → species Pongo indicus
• Species Siv. indicus → subspecies Po. i. indicus
• Species Siv. sivalensis → subspecies Po. i. sivalensis
• Species Siv. parvada → subspecies Po. i. parvada

Genus Gigantopithecus → species Pongo blacki
• Species Gi. blacki → subspecies Po. b. blacki
• Species Gi. giganteus → subspecies Po. b. giganteus
• Species Gi. bilaspurensis → subspecies Po. b. bilaspurensis

Subfamily Kenyapithecinae → genus Kenyapithecus
• Genus Ouranopithecus → species Ke. macedoniensis
• Genus Pierolopithecus → species Ke. catalaunicus
• Genus Græcopithecus → species Ke. freybergi
• Genus Kenyapithecus → species Ke. wickeri

Genus Ouranopithecus → species Kenyapithecus macedoniensis
• Species Ou. macedoniensis → species Ke. macedoniensis

Genus Pierolopithecus → species Kenyapithecus catalaunicus
• Species Pi. catalaunicus → species Ke. catalaunicus

Genus Græcopithecus → species Kenyapithecus freybergi
• Species Gr. freybergi → species Ke. freybergi

Genus Kenyapithecus → species Kenyapithecus wickeri
• Species Ke. wickeri → species Ke. wickeri



V.a-3.) Compromise

Family Hominidae
• Genus Homo
• Subgenus H. (Anthropus)
• Infragenus H. (A. Palæoanthropus)
• Species H. (A. Pa.) sapiens
• Subspecies H. (A. Pa.) s. sapiens
• Subspecies H. (A. Pa.) s. idaltu
• Species H. (A. Pa.) neanderthalensis
• Species H. (A. Pa.) heidelbergensis
• Species H. (A. Pa.) antecessor
• Infragenus H. (A. Pithecanthropus)
• Species H. (A. Pi.) floresiensis
• Species H. (A. Pi.) cepranensis
• Species H. (A. Pi.) erectus
• Subspecies H. (A. Pi.) e. erectus
• Subspecies H. (A. Pi.) e. pekinensis
• Subspecies H. (A. Pi.) e. yuanmouensis
• Subspecies H. (A. Pi.) e. tautavelensis
• Subspecies H. (A. Pi.) e. soloensis
• Subspecies H. (A. Pi.) e. lantianensis
• Subspecies H. (A. Pi.) e. nankinensis
• Subspecies H. (A. Pi.) e. bilzingslebenensis
• Subspecies H. (A. Pi.) e. palaeojavanicus
• Subspecies H. (A. Pi.) e. georgicus
• Species H. ergaster > subspecies H. s. ergaster
• Species H. rudolfensis > subspecies H. afr. rudolfensis
• Species H. naledi > subspecies H. afr. naledi
• Species H. habilis > subspecies H. afr. habilis
• Species H. antiquus > subspecies H. afr./afa. antiquus
• Subgenus H. (Australopithecus)
• Infragenus H. (Au. Gracilis)
• Species H.(Au. Gr.) habilis
• Subspecies H. (Au. Gr.) h. habilis
• Subspecies H. (Au. Gr.) h. rudolfensis
• Species H. (Au. Gr.) africanus
• Subspecies H.(Au. Gr.) afr. africanus
• Subspecies H. (Au. Gr.) afr. sediba
• Subspecies H. (Au. Gr.) afr. habilis
• Species H. (Au. Gr.) afarensis
• Subspecies H. (Au. Gr.) afa. anamensis
• Subspecies H. (Au. Gr.) afa. afarensis
• Subspecies H. (Au. Gr.) afa. platyops
• Subspecies H. (Au. Gr.) afa. bahrelghazali
• Subspecies H. (Au. Gr.) afa. garhi
• Subspecies H. (Au. Gr.) afa. antiquus
• Infragenus H. (Au. Paranthropus)
• Species H. (Au. Par.) aethiopicus
• Species H. (Au. Par.) deyiremeda
• Species H. (Au. Par.) robustus
• Species H. (Au. Par.) boisei
• Species H. (Au. Par.) walkeri
• Subgenus H. (Pan)
• Infragenus Not Applicable
• Species H. (Pan) troglodytes
• Species H. (Pan) paniscus
• Subgenus H. (Dryopithecus)
• Infragenus H. (D. Samburupithecus)
• Species H. (D. S.) kiptalami
• Infragenus H. (D. Anoiapithecus)
• Species H. (D. A.) brevirostris
• Infragenus H. (D. Nakalipithecus)
• Species H. (D. N.) nakayamai
• Infragenus H. (D. ?)
• Species H. (D. ?) fontani
• Species H. (D. ?) wuduensis
• Species H. (D. ?) laietanus
• Species H. (D. ?) crusafonti
• Subgenus H. (Chororapithecus)
• Infragenus Not Applicable
• Species H. (C.) abyssinicus
• Subgenus H. (Gorilla)
• Genus Pongo
• Subgenus P. (Gigantopithecus)
• Subgenus P. (Sivapithecus)



V.a-4.) Discussion of Approaches



Works Cited



Ackermann, Rebecca Rogers; Rogers, Jeffery; Cheverud, James M., “Identifying the morphological signatures of hybridization in primate and human evolution.” Journal of Human Evolution 51, Pages 632-645 (Recieved 2 Feb. 2006; accepted 18 July 2006)
Available online @ <http://www.sciencedirect.com>



Begun, David R. Miocene Hominids and the Oirigin of the African Apes and Humans. Review in Advance. (2010)
<http://anthro.vancouver.wsu.edu/media/Course_files/anth-490-edward-h-hagen/begun-2010-miocene-hominids-and-the-origins-of-the-african-apes-and-humans.pdf>



Berger, Lee R. & McHenry, Henry M., “Body proportions in Australopithecus afarensis and A. africanus and the origin of the genus Homo.” Journal of Human Evolution Volume 35, Issue 1, Pages 1-22 (July 1998)



Choi, Charles Q., “Fossils Shed New Light on Human–Gorilla Split.” Scientific American / Live Science (12 Feb 2016)
<https://www.scientificamerican.com/article/fossils-shed-new-light-on-human-gorilla-split/>



Dawkins, Richard. The Ancestor's Tale: A Pilgrimage to the Dawn of Life. Houghton Mifflin. 2004
<https://en.wikipedia.org/wiki/The_Ancestor's_Tale>



Dawkins, Richard. “Is Evolution Predictable?” Lecture. ScienceNET. Jun 15, 2015
<https://www.youtube.com/watch?v=1gjUXT99gC0>



Diamond, Jared. The Third Chimpanzee: The Evolution and Future of the Human Animal. 3Rd ed. Hutchinson Radius. 1991 (Previous titles: Rise and Fall of the Third Chimpanzee: How Our Animal Heritage Affects the Way We Live. 1st ed. 1991-2004; changed to The Rise and Fall of the Third Chimpanzee: Evolution and Human Life. 2nd ed. 2004-2006)
<http://en.m.wikipedia.org/wiki/The_Third_Chimpanzee>



Futuyma, Douglas J. & Mayer, Gregory C. “Non-Allopatric Speciation in Animals.” Systematic Zoology 29(3), Pages 254-271 (1980)
<https://www.jstor.org/stable/2412661?seq=1#page_scan_tab_contents>



Green, David J., Adam D. Gordon & Brian G. Richmond. “Limb-size proportions in Australopithecus afarensis and Australopithecus africanus.” Journal of Human Evolution 52 (2007) 187e200. Received 17 November 2005; accepted 4 September 2006
<http://www.albany.edu/~ag856732/Greenetal2007JHE.pdf>



Haeuslera, Martin & McHenry, M. “Body proportions of Homo habilis reviewed.” Journal of Human Evolution, Volume 46, Issue 4, Pages 433–465 (April 2004)
<http://dx.doi.org/10.1016/j.jhevol.2004.01.004>



Haile-Selassie, Yohannes; Melillo, Stephanie M.; Su, Denise F. The Pliocene hominin diversity conundrum: Do more fossils mean less clarity? Review in Advance. (7 January 2017)
<http://www.pnas.org/content/113/23/6364.full.pdf>



Handwerk, Brian. “Human, Chimp Ancestors May Have Mated, DNA Suggests.” National Geographic News (17 May 2006)
<http://news.nationalgeographic.com/news/2006/05/humans-chimps.html>



IJdo, J.W.., Baldini, A., Ward, D.C. and Wells, R.A. “Origin of human chromosome 2: An ancestral telomere-telomere fusion.” Proc. Natl. Acad. Sci. USA. Vol. 88 (October 1991): pp. 9051-9055; Genetics
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC52649/pdf/pnas01070-0197.pdf>



Jungers, William L. “Letters to Nature.” Nature 297 (24 Jun. 1982): 676-678 doi:10.1038/297676a0
<http://www.nature.com/nature/journal/v297/n5868/abs/297676a0.html>



McBrearty, Sally & Nina G. Jablonski. “Letters to Nature.” Nature 437, 105-108 (1 Sep. 2005) doi:10.1038/nature04008; Received 31 January 2005; Accepted 4 July 2005
<http://www.nature.com/nature/journal/v404/n6776/full/404382a0.html>



McCrossin, M.L., Benefit, B.R., Gitau, S.N., Palmer, A.K., Blue, K.T. “Fossil evidence for the origins of terrestriality among the Old World higher primates.” Primate locomotion: recent advances. New York: Plenum Press. 1998
<https://www.researchgate.net/publication/290062296_Fossil_Evidence_for_the_Origins_of_Terrestriality_among_Old_World_Higher_Primates>



Nachman, M. W., S. N. Boyer, J. B. Searle and C. F. Aquadro, 1994. Mitochondrial DNA variation and the evolution of Robertsonian chromosomal races of house mice, Mus domesticus. Genetics 136(3): 1105-1120.
<http://www.talkorigins.org/indexcc/CB/CB141.html>



Niemitz, Carsten. The evolution of the upright posture and gait—a review and a new synthesis. NCBI. 2010 Mar; 97(3): 241–263. Published online 2010 Feb 3. doi: 10.1007/s00114-009-0637-3
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819487/>



Patterson, Nick, Richter, Daniel J., et al. “Genetic evidence for complex speciation of humans and chimpanzees.” Nature 441 (29 June 2006): 1103-1108; doi:10.1038/nature04789; Received 5 November 2005; Accepted 7 April 2006; Published online 17 May 2006;
<http://www.nature.com/nature/journal/v441/n7097/full/nature04789.html>



Richmond, Brian G. & David S. Strait. “Letters to Nature.” Nature 404 (23 Mar. 2000): 382-385 | doi:10.1038/35006045; Received 10 Aug. 1999; Accepted 10 Jan. 2000
<http://www.nature.com/nature/journal/v404/n6776/full/404382a0.html>



Richmond, Brian G.; Aiello, L. C.; Wood, B. A. “Early hominin limb proportions” Journal of Human Evolution 43(4) (Oct. 2002): 529-48


Scally, A., Dutheil, J.Y., Hillier, L.W., et al. “Insights into hominid evolution from the gorilla genome sequence.” Nature. 483 (08 Mar. 2012): 169-175; doi:10.1038/nature10842;
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3303130/>



Shigehiro Katoh, Yonas Beyene, Tetsumaru Itaya, Hironobu Hyodo, Masayuki Hyodo, Koshi Yagi, Chitaro Gouzu, Giday WoldeGabriel, William K. Hart, Stanley H. Ambrose, Hideo Nakaya, Raymond L. Bernor, Jean-Renaud Boisserie, Faysal Bibi, Haruo Saegusa, Tomohiko Sasaki, Katsuhiro Sano, Berhane Asfaw & Gen Suwa. New geological and palæontological age constraint for the gorilla–human lineage split.Nature 530, 215–218 (11 February 2016) doi:10.1038/nature16510 Received 27 September 2015 Accepted 03 December 2015 Published online 10 February 2016
<http://www.nature.com/nature/journal/v530/n7589/full/nature16510.html>



Venema, Dennis. “Denisovans, Humans, and the Chrosome 2 Fusion.” Biologos (06 Sep. 2012):
<http://biologos.org/blogs/archive/denisovans-humans-and-the-chromosome-2-fusion>



Wakeley, John. “Complex speciation of humans and chimpanzees.” Nature. 452 (Mar. 2008): E3–4; discussion E4. doi:10.1038/nature06805; Received 22 Feb. 2007; Accepted 17 Jan. 2008
<http://www.nature.com/nature/journal/v452/n7184/full/nature06805.html>



Yong, Ed. “Genetic neoteny – how delayed genes separate human brains from chimps.” Discover Magazine / Not Exactly Rocket Science. (Mar. 24 2009)
<http://blogs.discovermagazine.com/notrocketscience/2009/03/24/genetic-neoteny-how-delayed-genes-separate-human-brains-from-chimps/#.WV-mRVGQy1s>


http://frontiersofzoology.blogspot.com/2012/04/