HOMININ EVOLUTION

EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> METAZOA> BILATERIA> DEUTEROSTOMATA> CRANIATA> VERTEBRATA> GNATHOSTOMATA> TETRAPODA> AMNIOTA> MAMMALIA> PRIMATES> HOMINOIDEA> HOMINIDAE> HOMININAE> HOMININI

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Description of Class

Hierarchical Classification

INTRODUCTION TO THE HOMININAE

Evolution of the primates (Figure 1), and especially the apes, the Hominidae, has been of general interest since Darwin’s publication of The Origin (Darwin 1859). Even when he wrote The Descent of Man (Darwin 1871), the fossil evidence was only a partial Neanderthal skeleton. He did predict, though, that the fossil evidence would likely be found on the African continent where our closest living relatives now reside. The picture of hominid evolution is far from complete, but the number of taxa within our line, the Homininae (hominins), has grown steadily since the 19th century. In addition, topology of the hominin branch of the primate tree has changed from a linear sequence of taxa to one of many branches pruned by local extinctions.

The earliest ape-like primate seems to have been a tailless transitional catarrhine called Proconsul (Figure 2). Its skeletal and dental remains have been found in Kenya and Uganda from strata ranging in age from 23-15 million years old (the first half of the Miocene; see Stringer and Andrews 2005). Three species have been recognized and vary in size from small forms (11-36 kg) to large animals (~76 kg). Furthermore, they seem to have exhibited sexual dimorphism (males ~1.3X larger than females). Aside from lacking a tail, Proconsul had a mix of ape and old world monkey characters. The one complete skull that has been found shows obvious monkey-like characters like a narrow nose, short face, and lack of brow ridges. The post cranial skeletons show that the animals had a pronograde stance (4-legged) and long, supple spinal column. However, they were unable to reach over their heads and hang by their forearms like current apes can. Nonetheless, these animals were well at home in the trees scampering in the branches as monkeys do today. They occurred in closed forest and forest edge habitats. Likely, this animal was a sister to the Hominoidea (the apes) rather than a member of the group.

ORIGIN OF THE APES

The earth during the Miocene epoch (23-5 mya, Figure 3 Left) was warm and saw the proliferation of forested lands across the African-Eurasian supercontinent (Potts 1996). The climate experienced a maximum around 17 mya and then a gradual cooling trend began to occur. The movement of the African plate into Europe began the uplift of mountains across southern Europe and into Anatolia (present-day Turkey). Near the end of the Miocene, the Mediterranean Sea was blocked multiple times with an ensuing dehydration of the basin. This period, called the Messinian salinity crisis (Garcia-Castellanos and Villasenor 2011), must have caused powerful environmental changes in the lands that border the Mediterranean basin. In addition, the upper half of the Miocene saw a gradual cooling with the concomitant growth of continental ice on Antarctica. The Miocene also saw the appearance and radiation of early apes (>100 ape species) throughout the open woodlands of Africa-Eurasia.

Dryopithecus (Figure 3 Right) was one of the wide-ranging genera that appeared in the second half of the Miocene following the contact of Africa with Eurasia, and its remains have been found from France to Hungary. The animal was about 0.6 meters long and weighed approximately 14 kg. Superficially, Dryopithecus resembled a small chimpanzee and seems to have been adapted to open woodlands. It was a generalist and had mobility of its shoulder joint that allowed it to hang, but it could not knuckle-walk. The suspensory lifestyle of Dryopithecus made it similar both to the Asian and African apes. It has been allied to both lines of apes and may be close to the common ancestor of the living great apes (Pongidae + Hominidae). In its body size and life style, Dryopithecus resembled most the gibbons of south-eastern Asia. Because the dryopithecines may well have given rise to the Asian and African apes supports a “Back-to-Africa” scenario in which the Hominoidea originated in Africa and then dispersed through suitable habitats in Eurasia. The dryopithecines, the basal members of the Hominidae according to Moya-Sola et al. (2009), radiated within Eurasia and then dispersed back into Africa giving rise to the African apes. The analysis of Moya-Sola et al. (2009) also suggests that the Hylobatidae are not members of the Hominoidea. We are working with the hypothesis that the dryopithecines are members of the Hominoidea and sisters to the major taxa of living apes as defined by Wilson and Reeder (2005; see Table 1). This taxonomy also is consistent with the cladogram of Figure 1. The accepted system of Hominoidea has two families and 23 extant species (see Table 1).

The most likely living sister of our species is the line of chimpanzees (common and bonobo). These have been sequenced and compared with Homo sapiens. Molecular analyses suggest that the genetic similarities between Homo and Pan are so great that all chimpanzees should be placed in the genus, Homo (Page and Goodman 2001; Wildman et al. 2003). Curiously, Linnaeus also named the Common Chimpanzee Homo trogylodites, in recognition of the similarities. Most commonly, Homo and Pan are placed in the same tribe, Hominini, and all taxa within the tribe are called hominins. The separation of Homo and Pan occurred near the end of the Miocene and beginning of the Pliocene epochs (~5-6 mya; Page and Goodman 2001). Indeed, The Pliocene and Pleistocene epochs encompass the period of hominin radiation.

The penchant for splitting, particularly at the generic and species levels has produced a confusing and chaotic stream of names. For example, the robust australopithecine Paranthropus boisei might be known as Zinjanthropus boisei or Australopithecus boisei as synonyms, any of which might be found in the literature. If Pan (the genus of chimpanzees) is immersed within Homo, then all of the generic diversity disappears. All hominin taxa would be in the genus Homo. Unfortunately, that proposal has not been accepted generally among biologists and physical anthropologists. Table 2 is a comprehensive list of bipedal hominin species which also appear in Figure 4. Those taxa that have an asterisk are recognized as distinct.

TABLE 1. The system of the extant Hominoidea, the apes, after Wilson and Reeder (2005). The number in parentheses following the generic name is the number of species within that genus.

Superfamily Hominoidea
- Family Hylobatidae (gibbons, the lesser apes)
  - Hylobates (7), Hoolock (2), Symphalangus (1), Nomascus (6)
- Family Hominidae (hominids, the great apes)
  - Subfamily Ponginae (orangutans)
    - Pongo (2)
  - Subfamily Homininae
    - Gorilla (2), Homo (1), Pan (2)

TABLE 2. Bipedal hominins arranged according to grades following the separation from the line leading to chimpanzees. The species are designated according to an extreme splitting taxonomy (all of the species are separate and distinct) and an extreme lumping taxonomy (taxa with an asterisk). We have underlined the binomials that we describe in the text. The table is a modification of Table 1 in Wood (2010).
GRADE	SPECIES INCLUDED IN A SPLITTING TAXONOMY
POSSIBLE HOMININS	Ardipithecus ramidus* Orrorin tugensis Sahelanthropus tchadensis Ardipithecus kadabba
ARCHAIC HOMININS	Australopithecus africanus* Australopithecus afarensis* Australopithecus bahrelgazali Australopithecus anamensis Australopithecus garhi Kenyanthropus platyops Australopithecus sediba
MEGADONT ARCHAIC HOMININS	Paranthropus robustus* Paranthropus boisei Paranthropus aethiopicus
TRANSITIONAL HOMININS	Homo habilis* Homo rudolfensis
PREMODERN HOMO	Homo erectus* Homo neanderthalensis Homo heidelbergensis Homo ergaster Homo antecessor Homo floresiensis
ANATOMICALLY MODERN HOMO	Homo sapiens*
A lumping taxonomy might recognize only these. Taxa underlined are described below.

THE BIPEDAL HOMININS: POSSIBLE PRIMITIVE MEMBERS

Most of the bipedal hominin radiation occurred during the Pliocene (5.3-2.5 mya) and Pleistocene (2.5-0.012 mya) epochs. The end of the Miocene was relatively warm, but at the end of a gradual cooling trend. The cooling trend continued through the Pliocene and into the Pleistocene, when the amplitudes of the climatic swings became very great during a time of extremely unsettled and variable climatic shifts. The last 1.5 million years was especially unsettled with glacial advances and relatively warm interglacial periods.

The earliest grade of bipedal ape, the possible hominin grade, was represented by Sahelanthropus (~7 mya, Figure 5 top right and top left) and Ardipithecus (~6.0-4.2 mya, Figure 5 bottom left and bottom right) from eastern Africa. These possible hominins are important in that their fossil remains have been dated near the separation of the human-chimp line. Sahelanthropus was found in Chad, very far from the Rift Valley and South Africa where almost all other early hominin remains had been found and around the time when the Sahara Desert had just begun to form (Schuster et al. 2006). Its presence in central Africa suggests that the hominins may have ranged much more widely on the African continent (Brunet et al. 2002). Brunet (2012) describes Sahelanthropus, which is known only from features of the skull, as having a suite of primitive and derived characters that make it unlikely to be a precursor to the chimpanzee line. Also, it lived in a mosaic of woodland and open spaces, a landscape more like that of the bipedal hominins. Thus, the postcranial skeleton likely will be somewhat similar to that of Ardipithecus.

Postcranial remains of Ardipithecus ramidus are known for females only. They were bipedal but had a foot with a divergent toe (Haile-Selassie et al. 2012). The interpretation was that they must have been arboreal, at least part of the time. Indeed, their remains were found in association with plants that occur in forests. The upper body had the proportions of a chimpanzee and range of movement in the shoulder that suggested an animal well adapted to climbing and swinging in the trees. This seemed to support the theory that bipedalism did not evolve in animals adapted to life in the savannahs, but rather by animals that brachiated and walked on limbs very much like orangutans do. If so, bipedal stance evolved in the trees well before our line began to walk on the ground. Aside from bipedality, Ardipithecus resembled chimpanzees. The brain case was about 300-350 cc in volume (females) and they weighed about 50 kg. Also, females were approximately 120 cm tall.

ARCHAIC AND MEGADONT HOMININS

Among the archaic hominin grade animals two are well-represented in the fossil record: Australopithecus afarensis and Australopithecus africanus. Australopithecus afarensis had a brain volume that ranged from 375-550 cc and showed significant sexual dimorphism. Males stood 152 cm tall and weighed up to 42 kg, and females were smaller (~107 cm tall and 29 kg). They lived between 3.9 and 3.0 mya in eastern Africa. Unlike Ardipithecus, Au. afarensis had a foot more like ours and a fully bipedal gait (Haile-Selassie et al. 2012), as demonstrated by a famous trackway in Laetoli, Tanzania (see Figure 6). The upper body still had adaptations for hanging and climbing in trees. These were animals of variable habitats: forest edges and savannahs. Australopithecus africanus must have emerged from the Au. afarensis line. They appeared in the fossil record around 2.8 mya and persisted for about a half million years. These australopithecines were the same size or slightly smaller than their predecessors (males 140 cm and females 110 cm). Their brain volume also was comparable. Australopithecus africanus, seemed to be more dedicated to a terrestrial lifestyle.

Australopithecus africanus appeared to be in the line to the megadont archaic hominins which persisted from 2.5 to 1.0 mya (Wood 2010). These are represented by Paranthropus robustus, whose remains have been found through eastern, southern, and western Africa. Adults ranged in size from 1.1 m (females) to 1.3 m (males) and had a brain volume of about 530 cc. Most notable are their teeth, which are quite large, especially the molars. An isotopic examination of their teeth confirmed that their diet was made up of plants, with a large proportion being grasses (Cerling et al. 2011). This line diverged from the hominins that gave rise to us and died out around 1 mya.

THE GENUS HOMO

The transitional hominins are represented by Homo habilis (~1.44-2.3 mya) who occupied sites through eastern Africa. This hominin had a brain volume that exceeded 500 and approached 800 cc. Considering their small size (females -1m, 32 kg and males 1.4m, 37 kg), the relative brain volume was fairly large. In addition, their remains have been associated with particular types of stone tools, usually choppers made of lava (Figure 7 Left).

Premodern Homo includes a set of taxa that begin with Homo erectus who stood 145 cm (female) to 185 cm (male, see Figure 8 Left). Their brain volume also was much larger ranging 750 to 1225 cc. These were bipedal apes that resembled us and moved like us. There is evidence for the controlled use of fire and butchered animals with marks on the bones made by a particular tool kit. They seemed to have ranged through Africa and then moved into suitable habitats through southern Asia and possibly into southern Europe. They appeared in the fossil record around 1.8 mya and disappeared only around 300,000 years ago. During the 1.5 million year period they gave rise to the common ancestor of Homo sapiens and Homo neanderthalensis. This transitional hominin was Homo heidelbergensis (Figure 9 Left). As the name implies, the first identified remains were found in Heidelberg, Germany. However, fossils assigned to H. heidelbergensis occur into Asia and Africa. These hominins were tall (males 175 cm and females 157 cm) with brain volumes (1100-1400 cc) that were substantially larger than H. erectus. They appeared in the fossil record around 700 kya and disappeared 300 kya when our species emerged.

NEANDERTHALS

Homo neanderthalensis (Neanderthal, Figure 9 Right) appeared around 500 kya either from Homo erectus or Homo heidelbergensis in southern Europe. Neanderthals were stocky (155 cm, 54 kg -females and 164 cm, 64 kg -males) and heavily muscled. They lived through southern Europe, the middle east and possibly east toward present-day Georgia. Animal remains associated with Neanderthals show evidence of butchering as do Neanderthal remains, suggesting ritual cannibalism. They seem to have been scavengers and also used spears to kill large animals up close. This was supported by Berger and Trinkhaus (1995, Figure 10) who compared the types of injuries sustained by Neanderthals to typical injuries inflicted on those who work in various risky occupations. They found that the suite of injuries as evidenced by broken bones was most similar to trauma sustained by rodeo competitors. Neanderthals developed a tool kit of stone, wood, bone, tusks, and antlers that was more complex than that of H. erectus and was comparable in sophistication to the tool kits of early modern humans (see Figure 7 Right).

Neanderthals also seem to have had a concept of ritual. We have mentioned possible ritual cannibalism, but they also may have had rituals associated with burials. There does not seem to be evidence of Neanderthal art or symbolic communication. Nevertheless, Neanderthals and Heidelbergensis both had the proper anatomical structures for vocal communication (Barney et al. 2012). For example, the hyoid bones of all three species are indistinguishable. The resonating chamber of Neanderthals would have made sounds that are more nasal and higher pitched that in modern humans. Furthermore, Krause et al. (2007) report that Neanderthals had the same derived FOXP2 gene, the so-called language gene, as modern humans.

Homo sapiens and Homo neanderthalensis may have interacted directly. For example, they both occupied sites in Palestine, but it is unclear as to whether they occupied those sites simultaneously. Finlayson (2009) suggests that the Neanderthals formed a barrier to the expansion of modern humans into the Levant from the Nile valley. There must have been some interaction, though. Neanderthal DNA markers have been found in the genomes of modern humans, exclusive of subsaharan Africans and native Australians (see below).

The fate of the Neanderthals has been an enduring question. Did we displace them or did modern humans move into regions that had been abandoned by the Neanderthals? Stringer (2011, 2012) says that the differences between Modern Human and Neanderthal group structure may have led to their demise. That is, Neanderthal groups seemed to be small, about 20-30 individuals. Human groups, however, were larger than 100. He suggested that the larger, multigenerational groups of humans were able to maintain cultural knowledge and allow for specialization thus promoting technological innovations.

Recent proposals include a catastrophic disease brought by modern humans (Wolff and Greenwood 2010), Transmissible Spongiform Encephalopathies (TSE) through ritual cannibalism (Underdown 2008), and an inability to respond to drastic climatic change (d’Errico et al. 2003). The last scenario does seem more likely. Despite common belief, Neanderthals may not have been particularly well adapted to cold. Rae et al. (2011), in a detailed study of the Neanderthal face, conclude that the face was not “likely to be an adaptation to resist cold stress”. Longo et al. (2012) invoke the mechanism of direct competition between modern humans and Neanderthals based on a study of a site in northern Italy which seems to have been occupied by both groups around 35 kya, the time when Neanderthal remains disappear from the fossil record throughout most of Eurasia. They did persist in a small population on Gibraltar, at the tip of the Iberian peninsula until about 24 kya (Carrion et al. 2008; Lopez-Garcia et al. 2011; Pachero et al. 2012) and are best known from a site known as Gorham’s Cave.

MODERN HUMANS

The phenomenal rise of modern humans and their spread across the face of the earth occurred in a very brief period of geologic time. Tattersall (2012) argues that the coalescence of characters that supported the success of Homo sapiens sapiens came together only between 100 and 60 kya though our species had been around for more than three times that period. The earliest members of our species were called Anatomically Modern Humans (AMH), and they differed little in overall body form from their immediate archaic ancestors (Tattersall 2012, Stringer 2011). Typically, they had a suite of characters that separated them from their archaic ancestors, likely Homo heidelbergensis in Africa. Most of the differences relate to characters of the skull (see Figure 12). Stringer (2011) lists the following most obvious characters that separate AMH from archaic humans:
– a large brain volume
– neurocranial globularity (the curvature and doming of the bones of the brain case)
– a brain case that is wider at the top when viewed from behind
– a high and evenly-arched temporal bone on the side of the skull
– small face that is tucked under the cranium
– small and divided brow ridge
– a narrow area of bone between the eye sockets
– increased projection of the middle of the face and nose
– a bony, projecting chin
– simplification and shrinkage of tooth crowns

These characters did not emerge together. Hublin et al. (2017) report remains from Jebel Irhoud in Morocco that appear to be H. sapiens and are dated to about 300kya. The earliest relatively complete skulls from Jebel Irhoud have robust but modern-looking faces; however, the brain case is long and low like those of Neanderthals. Thus, modern features evolved as a mosaic with the face changing before the brain case.

The skulls of modern humans from an area near Herto, a village in Ethiopia, had the rounded dome cranium that is typical of Homo sapiens. They were dated at 160 kya by White et al. (2003), though McDougall et al. (2005) proposed a much older date (~195 kya). More recently, White et al. (2003), who found and described the Herto skeletal remains, considered them to be different enough to warrant a separate subspecies designation: Homo sapiens idaltu (Figure 13). Like the archaic human ancestors, the Herto skulls had more robust features like heavy brow ridges; however, the brow ridges did show a separation. Thus, by the time of the Herto people, they had a domed cranium with a small face (Smith et al. 2012).

Templeton (2002) reports evidence of Homo sapiens on the Arabian Peninsula at 140 kya. Indeed, AMH seem to have occupied that part of the Middle East for many thousands of years. At that time the grassland savannah from eastern Africa stretched unbroken into the Levant. Thus, from the perspective of a wandering human group, that part of the eastern Mediterranean was a continuous part of their homeland with the same plants and animals. Human remains dated at 100 kya from the Skhul cave on Mt. Carmel in Israel show a mix of primitive and modern features (Figure 14). Tattersall (2012) offers several possible explanations for the primitive nature of their skulls. They may have been remnants of an early expansion of AMH from Africa, which, as mentioned earlier, was an ecological extension of eastern Africa. The most intriguing possibility is that the skulls with robust features are the results of interbreeding between modern humans and Neanderthals, which did occupy the area at the same time and even appeared to out compete modern humans for a time in that place.

Both paleontological and genetic evidence point to the continent of Africa as the origin of modern humans. Cann et al. (1987) isolated mitochondria from 147 people who came from five geographic regions of the world. They compared restriction analyses of the isolates and proposed that all members of their sample came from a woman who lived in Africa about 200 kya. More recently, Ingman et al. (2000) compared the mitochondrial genomes of 53 humans from across the globe and came up with an estimate of 99-140 kya for the most recent common ancestor of the mitochondrial genome. In keeping with an African origin, mitochondrial diversity with attendant deep branching is greatest on the African continent. All other mitochondrial genomes are descended from the genome with the L3 marker (see Figure 15), which gave rise to the N and M lines. The expansion of this group occurred fairly rapidly across Eurasia. Modern humans expanded across southern Asia and into Australia before 50 kya. That was followed by the human expansion across Europe and central Asia, from which the Americas were occupied.

Mitochondria are inherited through matrilineal descent because sperm do not contribute mitochondria to the zygote. Thus, the last common mitochondrial ancestor was dubbed mitochondrial Eve. On the other hand, because the y-chromosome is contributed only by the male parent, the last common ancestor was called the genetic Adam. Markers on the y chromosome show similar patterns of descent across Eurasia, Australia, Polynesia, and the Americas. Early work (e.g. Underhill et al. 2001) suggested a much later date for the last common y-chromosome ancestor, but Poznik et al. (2013) demonstrated that the last common ancestor of the y chromosome lived 120-156 kya, which overlaps well with the range for mitochondrial Eve.

During the climatic instability of the late Pleistocene, our species appeared. The glacial periods locked up large amounts of water, which produced extensive drought and desertification in Africa. Thus, our species was periodically restricted to small islands of suitable habitat during the Wisconsin (85-11 kya) and Illinois (~191-130 kya) glacials (see Figure 16). The intervening interglacial (Sangamon, 125-75 kya) was wet, allowing the savannah to expand into most of the Saharan region which became dotted with lakes and streams. At the end of the interglacial around 100-75 kya, desert began to return to the Sahara and likely induced human migrations from northern and eastern Africa. At the onset of the Wisconsin glaciation, Mt Toba, a super volcano on Sumatra, Indonesia exploded with the greatest force of any eruption during the past 2.5 MY (Ambrose 1998). The explosion occurred around 71-75 kya and plunged the earth into the coldest period during the Pleistocene. Estimates of its impacts suggest that Africa and Eurasia experienced 6-10 years without a summer and the recovery took about a thousand years. Ambrose (1998) suggests that the explosion and its aftermath could have restricted human breeding populations to very small groups (10,000 or fewer) in which genetic drift could give rise to new humans with new ways of thinking and communicating. Diamond (1999) called this relatively sudden change in behavior The Great Leap Forward and others (e.g. Binford 1985) called it The Human Revolution.

The correspondence between the end of the Illinois glacial and the appearance of Mitochondrial Eve and Genetic Adam suggests that human populations were restricted into small habitat islands causing genetic bottlenecks well before the explosion of Mt. Toba. McBreaty and Brooks (2000) proposed that there was no real behavioral revolution, but the coalescence of behaviors occurred over a long period of time through exchange between populations. Then, during the wet interglacial, human groups with more modern behaviors began to appear and overwhelm (outcompete) other populations in Africa. Whether the change occurred suddenly or over a long period, it is referred to as cultural or behavioral modernity and manifests itself in expressions of symbolic thinking. The most obvious expression of symbolic thinking is complex language; however, before the advent of writing, complex communication can be inferred only from artifacts such as items of self-adornment like shell necklaces and red ochre, both of which were found in Blombos Cave, South Africa (dated at 100-77 kya; Henshilwood et al. 2002, Henshilwood et al. 2011, see Figure 17). In addition, modern humans left other evidences of archaeologically-accessible indications of behavioral modernity according to Calvin (2003) and Stringer 2011):

– experiment with different types of fine tools
– evidence of fishing (Figure 17)
– long-distance barter
– figurative art (Figure 17)
– evidence of game-playing
– evidence of music
– cooked and seasoned food
– ritual burial

Humans with these modified behaviors displaced all other populations of bipedal apes in Africa and across Eurasia making our species the last ape standing.

HOBBITS AND OTHER STORIES

The story of hominin evolution seemed to have been fairly well known by 2000. Homo erectus was the first hominin to expand its range from Africa. That was replaced in Europe by H. heidelbergensis, a group of which evolved into H. neanderthalensis. Homo sapiens then expanded its range in Africa, replaced all other bipedal apes and then emerged from Africa and replaced all other members of Homo. However, fossil discoveries beginning in 1991 but accelerating from 2004 to 2017 have complicated the simple version of the hominin story.

Some hominin fossils were unearthed at Dmanisi, Georgia (Vekua 2002), at the northern edge of the African-Levant region. These remains were associated with simple stone tools and dated at 1.8 mya, the oldest hominin remains outside of Africa (Gabunia et al. 2000). They were distinctive in how primitive they appeared, especially in details of the skull and brain volume (Figure 18). Indeed, Bermudez de Castro et al. (2014) interpreted the skulls to represent a range of variation that embraces most of the taxa considered to be different species within Homo. Thus, the comfortable story of replacement may just be an artifact of normal early variation within early Homo.

Later, while searching for the makers of simple stone tools on the Indonesian island of Flores, Brown et al. (2004) discovered a skull of a diminutive adult female associated with much of her post cranial skeleton. Not only was she small (about 1 meter tall), but her brain volume was only about 417 cm2 (Falk et al. 2005, see Figure 19). This was so small that the discoverers nicknamed LB1 the Hobbit and had to demonstrate that the hominin was not microcephalic, which Falk et al. (2005) did very convincingly. Indeed, they showed that the brain, though quite small, most closely resembled that of Homo erectus. Finlayson (2009) and others suggested that Homo erectus may have persisted on Flores and gave rise to a dwarfed island variant, which the discoverers called Homo floresiensis. Early attempts at dating the finds suggested that they were very recent (~13 kya, Brown et al. 2004), but Sutikna et al. (2016) demonstrated that the skeletal remains dated to 50-100 kya. Though the brain resembled the shape of H. erectus, aspects of the skull and post cranial skeleton appeared to be even more primitive and may represent an earlier expansion of a Dmanisi-like Homo across southern Asia (Falk 2011).

During 2010 the Max Planck Institute for Evolutionary Anthropology in Leipsig, Germany published the first draft of the nuclear genome of Neanderthal (Green et al. 2010) and the mitochondrial genome of an unknown hominin from a cave near Denisova, a village in southern Siberia (Krause et al. 2010). The outcomes of these sequences were surprising, but explainable. Comparisons between the Neanderthal and modern human genomes by Green et al. (2010) showed that non-African human genomes contain 1-4% Neanderthal DNA. This small but significant number suggests that a few successful matings between Neanderthal males and modern human females did occur after they left Africa, but before the general dispersal across Eurasia. Likely, this occurred in the Levant where the two species came into contact.

The Denisovan mitochondrial genome was taken from a single finger bone, and that individual lived between 30-50 kya (Krause et al. 2010). They showed that the Denisovans were quite different from both modern humans and Neanderthals. Until recently, the only additional fossils were a few teeth until a Denisovan partial lower jaw was found at high altitude in the Tibetan Plateau (Chen et al. 2019). This find, together with interpretations of the genome or proteome by Gokhman et al. (2019), produce a physical description of Denisovans as successful, wide-ranging, and deep-rooted sister to Neanderthals, whom they resembled (see Figures 20 and 21). That modern humans and Denisovans interbred can be seen in traces (3-5%) of the Denisovan genome can be found in the genomes of Asians, Polynesians, and Australians.

DNA taken from bones in a cave in Spain (Sima de los Huesos), which had been identified as Homo heidelbergensis, more closely resembles the DNA of Denisovans than that of Neanderthals (Meyer et al. 2014). Perhaps the Denisovans were descendants of H. heidelbergensis, as were the H. neanderthalensis and H. sapiens. This calls into question as to the origins of the three crown hominins as well as the origin of H. heidelbergensis. Could they have evolved from a group of Homo erectus in Eurasia and then moved back into Africa during an earlier interglacial period? Clearly, the story of our species has not been completed, and we are certain that many more surprises await discovery.

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By Jack R. Holt. Last revised: 04/29/2021


FIGURE 18. Skull of a Homo erectus found at Dmanisi, Georgia.	FIGURE 19. Skull of LB1, Homo floresiensis from Flores, Indonesia.

FIGURE 19. Interpretations of the Denisovan proteome relative to the skulls of modern humans and Neanderthals. Figure 10 from Gokhman et al. (2019).	FIGURE 20. Interpretations of the Denisovan proteome relative to the post cranial structure of modern humans and Neanderthals. Figure 11 from Gokhman et al. (2019).


FIGURE 2. Images of Proconsul. Left: Reconstruction of a skeleton on display at the University of Zurich. Photo by Guerin Nicolas. Right: Restoration of Proconsul by Nobu Tamura. Both images published under the Creative Commons license.


FIGURE 3. Left: The earth as it appeared at the beginning of the Miocene (~20 mya). Image used according to the Creative Commons license, created by 36ophiuchi. Middle: Sahelanthropus. Right: A reconstruction of Dryopithecus shown walking on the ground. Though it likely could have moved on the ground, its home probably was high in the trees.



FIGURE 5. Top Left: Sahelanthropus skull. Photo by Dider Descouns and used under the Creative Commons License. Top Right: A reconstruction of Sahelanthropus tchadensis by the Smithsonian Museum of Natural History. Bottom Left: A photograph of the frontal view of a digital reconstruction of a female Ardipithecus skull. Image from Smithsonian Museum of Natural History. Bottom Right: A reconstruction of a female Ardipithecus. Note the bipedal stance, divergent great toe, and long arms. Image from White et al. (2009).


FIGURE 6. Australopithecus afarensis. Left: An artist’s rendition of a pair of afarensis walking at Laetoli during an ash fall 3.4 mya. Right: A trackway unearthed by Mary Leakey at Laetoli, Tanzania. The footprints clearly show the bipedal gait of these archaic hominins. Images licensed through Creative Commons.


FIGURE 7. Typical tool kits of Homo habilis (left), Homo erectus (center), and Homo neanderthalensis (right). Images from the Smithsonian Institution Museum of Natural History.


FIGURE 8. Left: Homo erectus. Image from the Smithsonian Museum of Natural History. Right: Distributional map of Homo erectus from Athena Review, Vol. 4, No.1: Homo erectus.


FIGURE 9. Reconstructions of select Premodern Homo. Left: Homo heidelbergensis, Right: Homo neanderthalensis. Images from the Smithsonian Museum of Natural History.


FIGURE 10. A comparison of traumatic injury between Neanderthals and Rodeo riders. Figure modified from Berger and Trinkhaus (1995)	FIGURE 11. Distributional map of Homo neanderthalensis from the Wikimedia Commons.


FIGURE 13. The Herto skull showing the mixture of archaic and modern features. Named as a distinct subspecies of modern human (Homo sapiens idaltu) by White et al. (2003).	FIGURE 14. A modern human skull from Skhul cave on Mt. Carmel in Israel. Tattersall (2012) offers the possibility that these may be descendants of a modern human- Neanderthal mating.



FIGURE 17. Evidences of modern behavior. Top Left: Red Ochre with symbolic design (~100 kya, Blombos Cave, South Africa). Top Right: Fish Hook (East Timor, Indonesia ~ 10 kya). Bottom Left: Image of cave bear (Chauvet Cave, France ~ 30 kya). Bottom Right: Venus of Brassempouy (France ~40 kya).

HOMININ EVOLUTION

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