History as Literature / Lewis Mumford The City…


Lewis Mumford / Harcourt Brace Jovanovich, 1961

“Mid the wanderings of Paleolithic man, the dead were the first to have a permanent dwelling: a cavern, a mound marked by a cairn, a collective barrow.”

“The city of the dead antedates the city of the living. In one sense indeed, the city of the dead is the forerunner, almost the core, of every city. Urban life spans the historic space between the earliest burial ground for dawn man and the final cemetery, the necropolis, in which one civilization after another, has met its end.”


No computer replacement yet; I’m at the library, frustrated! My “vacation” from blogging will not do. I must blog!

Anyway: I’ve been going through piles of books to “dispense with” and reacquainting myself with the small stack of those which I return to again and again for inspiration and reference, and vitally, the handful of ideas that set me off on a journey many years ago toward understanding human behavior (which as an Asperger, is/was a critical topic. It is my hypothesis that Asperger types have a hyposocial, visually-based brain organization that “resembles” that of pre-social “Wild” Homo sapiens.)

The giant effort, The City in History, by Lewis Mumford, is one of those books. I have never read all 576 pages of exhaustive details; the quote above occurs near the beginning, and “struck me” immediately with its importance to modern human destiny; not predestined destiny, but the path of human civilization as it has played out over the previous 10-15,000 years of humans becoming domestic “urban” humans, a distinction that has become more “real” to me as I have explored this “thing” called Asperger’s.

Modern social destiny, and the “type” Homo sapiens that created it, (and whom continues to be created by hypersocial environments), was not a collective direction decided upon by “mankind” but the result of individuals pursuing survival. Climatic change and other natural geologic processes forced the dependence on agriculture and sedentary life; the “idea” of controlling nature must have seemed to be a great and victorious reality at the time, which could only be “good”. This quest remains the central “self-glorification” of modern techno-social humans, but from this one step, disaster has followed.

Mumford’s book is filled with the grandiose “narrative” that archaeologists and anthropologists envy – (frustrated novelists that they are.) Historians are free to “do this” – history has always been a scheme of cultural focus; mythology with either a few facts, or a deluge, added to “support” the myth. Our mistake is in thinking that mythology is “false” and has no value, and that history must be “scientific” – which it is not. It is literature that serves to remind us of the hundreds of millions of lives that have been lived, and great writers like Mumford remind us that “we are not IT” – that is, the supreme and intelligent species that fulfills some imaginary “historical” evolutionary destiny, but instead, our behavior shows us to be one more repetition of the necropolis stage of civilization.


Paleontology Lesson: “Splitting or Lumping” of fossils / Too many species

Yes, this is about dinosaurs, but the principle applies to the “every anthropologist who finds a fossil gets to name a new species” problem in Homo evolution, based on “skull” shape and dimensions rather than on “reproduction” as the evolutionary sign of speciation. Here, it’s developmental changes that have to be sorted out. Two articles:

New analyses of dinosaur growth may wipe out one-third of species

October 30, 2009

Read more at: https://phys.org/news/2009-10-bye-hogwarts-dinosaur-analyses-growth.html#jCp

(PhysOrg.com) — Paleontologists from the University of California, Berkeley, and the Museum of the Rockies have wiped out two species of dome-headed dinosaur, one of them named three years ago – with great fanfare – after Hogwarts, the school attended by Harry Potter.

Their demise comes after a three-horned dinosaur, Torosaurus, was assigned to the dustbin of history last month at the Society of Vertebrate Paleontology meeting in the United Kingdom, the loss in recent years of quite a few duck-billed hadrosaurs and the probable disappearance of Nanotyrannus, a supposedly miniature Tyrannosaurus rex.

These dinosaurs were not separate species, as some paleontologists claim, but different growth stages of previously named dinosaurs, according to a new study.

The confusion is traced to their bizarre head ornaments, ranging from shields and domes to horns and spikes, which changed dramatically with age and sexual maturity, making the heads of youngsters look very different from those of adults.

“Juveniles and adults of these dinosaurs look very, very different from adults, and literally may resemble a different species,” said dinosaur expert Mark B. Goodwin, assistant director of UC Berkeley’s Museum of Paleontology. “But some scientists are confusing morphological differences at different growth stages with characteristics that are taxonomically important. The result is an inflated number of dinosaurs in the late Cretaceous.”

Goodwin and John “Jack” Horner of the Museum of the Rockies at Montana State University in Bozeman, are the authors of a new paper analyzing North American dome-headed dinosaurs that appeared this week in the public access online journal PLoS One.

Unlike the original dinosaur die-off at the end of the Cretaceous period 65 million years ago, this loss of species is the result of a sustained effort by paleontologists to collect a full range of dinosaur fossils – not just the big ones. Their work has provided dinosaur specimens of various ages, allowing computed tomography (CT) scans and tissue study of the growth stages of dinosaurs.

In fact, Horner suggests that one-third of all named dinosaur species may never have existed, but are merely different stages in the growth of other known dinosaurs.

“What we are seeing in the Hell Creek Formation in Montana suggests that we may be overextended by a third,” Horner said, a “wild guess” that may hold true for the various horned dinosaurs recently discovered in Asia from the Cretaceous. “A lot of the dinosaurs that have been named recently fall into that category.”

The new paper, published online Oct. 27, contains a thorough analysis of three of the four named dome-headed dinosaurs from North America, including Pachycephalosaurus wyomingensis, the first “thick-headed” dinosaur discovered. After that dinosaur’s description in 1943, many speculated that male pachycephalosaurs used their bowling ball-like domes to head-butt one another like big-horn sheep, though Goodwin and Horner disproved that notion in 2004 after a thorough study of the tissue structure of the dome.

Many paleontologists now realize that the elaborate head ornaments of dinosaurs, from the huge bony shield and three horns of Triceratops to the coxcomb-like head gear of some hadrosaurs, were not for combat, but served the same purpose as feathers in birds: to distinguish between species and indicate sexual maturity.

“Dinosaurs, like birds and many mammals, retain neoteny, that is, they retain their juvenile characteristics for a long period of growth,” Horner said, “which is a strong indicator that they were very social animals, grouping in flocks or herds with long periods of parental care.”

These head ornaments, which probably had horny coverings of keratin that may have been brightly-colored as they are in many birds, started growing when these dinosaurs reached about half their adult size, and were remodeled as these dinosaurs matured, continuing to change shape even into adulthood and old age, according to the researchers.

In the new paper, Horner and Goodwin compared the bone structures of Pachycephalosaurus with that of a domeheaded dinosaur, Stygimoloch spinifer, discovered in Montana by UC Berkeley paleontologists in 1973, and a dragon-like skull discovered in South Dakota and named in 2006 as a new species, Dracorex hogwartsia.

With the help of CT scans and microscopic analysis of slices through the bones of Pachycephalosaurus and Stygimoloch, the team concluded that Stygimoloch, with its high, narrow dome, growing tissue and unfused skull bones, was probably a pachycephalosaur subadult, in a stage just before sexual maturity.

Dracorex is one of a kind, and thus unavailable for dissection, but morphological analysis indicates it is a juvenile that hasn’t yet formed a dome, although the top of its skull shows thickening suggestive of an emerging dome.

“Dracorex’s flat skull, nodules on the front end and small spikes on back, and thickened but undomed frontoparietal bone all confirm that, ontogenetically, it is a juvenile Pachycephalosaurus,” Goodwin said.

Comparison of these skulls to other fossils in the hands of private collectors confirm the conclusions, they said. In all, they looked at 21 dome-headed dinosaur skulls and cranial elements from North America.

The key to this analysis, Horner said, was years of field work in Montana by his team and Goodwin’s in search of fossils of all sizes.

“We have gone out in the Hell Creek Formation for 11 years doing nothing but collecting absolutely everything we could find, which is the kind of collecting that is required,” he said. “If you think about Triceratops, people had collected for 100 years and still hadn’t found any juveniles. And we went out and spent 11 years collecting everything, and we found all kinds of them.”

“Early paleontologists recognized the distinction between adults and juveniles, but people have lost track of looking at ontogeny – how the individual develops – when they discover a new fossil,” Goodwin said. “Dinosaurs are not mammals, and they don’t grow like mammals.”

In fact, the so-called metaplastic bone on the heads of horned dinosaurs grows and dissolves, or resorbs, throughout life like no other bone, Horner said, and is reminiscent of the growth and loss of horns today in elk and deer. In earlier studies, Horner and Goodwin found dramatic remodeling of metaplastic bone in Triceratops, which led to their subsequent focus on dome-headed dinosaurs.

“Metaplastic bones get long and shorten, as in Triceratops, where the horn orientation is backwards in juveniles and forward in adults,” Horner said. Even in older specimens, such as the fossil previously named Torosaurus, bone in the face shield resorbs to create holes along the margin. John Scannella, Horner’s student at Montana State, presented a paper reclassifying Torosaurus as an old Triceratops at the Society for Vertebrate Paleontology meeting in Bristol, U.K., on Sept. 25.

“In order for that huge amount of bone to move, there has to be a lot of deposition and resorption,” Horner said.

Horner and Goodwin continue to search for dinosaur fossils in the Hell Creek Formation, which is rich in Triceratops, dome-headed dinosaurs, hadrosaurs and tyrannosaurs. Analysis of growth stages in these taxa will have implications for other horned dinosaurs that are being uncovered in Asia and elsewhere.

“There are other horned dinosaurs I think may be over split,” that is, split into too many new species rather than being lumped together as one species, Goodwin said.

Source: University of California – Berkeley (news : web)




TOP: Immature Skull BOTTOM: Mature Adult Skull

UPDATE 2016 \/: Go to article for details and illustrations:

SAURIAN BLOG http://saurian.maxmediacorp.com/?p=893/

No more Demons and Dragon Kings? Pachycephalosaurus ontogeny

CLIP: On top of all that, some dinosaurs also appear to develop unique structures like horns, domes and crests at various points during their development, and many are quite dramatic, appearing very quickly during ontogeny. No wonder then that it was not uncommon for scientists to name several species of dinosaur found at the same time and same place differentiated largely by size and display structures. And possibly the best example of this situation was Pachycephalosaurus, Stygimoloch (“Styx demon”) and Dracorex (“dragon king”); found at the same time, in the same place, more closely related to each other than to other pachycephalosaurs, and differing only in size and cranial features. And then Dr. Jack Horner changed everything.

One of the most influential discoveries that has radically changed our understanding of dinosaurs and their world is the realization that dinosaurs often went through dramatic physical changes as they aged. It has been well known for some time that unlike modern birds, non-avian dinosaurs took several years to reach adult size and began breeding before reaching skeletal maturity, but shared with them very rapid growth rates, resulting in animals that ‘lived fast and died young’. Thanks to this growth habit, most dinosaurs that we have a significant sample size for show a particular pattern when it comes to their fossil record: hatchling and juveniles tend to be rare due to very high mortality rates (many were eaten and digested, resulting in no preservation), rapid growth rates to larger size and preservation bias that favors fossilization of large bodied, large boned animals. By comparison, there tends to be a large number of individuals that are one-half to two-thirds maximum adult size that represent animals that have reached sexual (but not skeletal) maturity, and a small number of individuals that have reached maximum adult size and skeletal maturity.


Paleontology Online / Fossil Focus: Encephalization in bipedal apes

A simple review of the “story” of “encephalized bipedal apes” as paleontologists see it.

Paleontology is not to be confused with anthropology: Paleontology is traditionally divided into various subdisciplines: Micropaleontology: Study of generally microscopic fossils, regardless of the group to which they belong. Paleobotany: Study of fossil plants; traditionally includes the study of fossil algae and fungi in addition to land plants. Palynology: Study of pollen and spores, both living and fossil, produced by land plants and protists. Invertebrate Paleontology: Study of invertebrate animal fossils, such as mollusks, echinoderms, and others. Vertebrate Paleontology: Study of vertebrate fossils, from primitive fishes to mammals. Human Paleontology (Paleoanthropology): The study of prehistoric human and proto-human fossils. Taphonomy: Study of the processes of decay, preservation, and the formation of fossils in general. Ichnology: Study of fossil tracks, trails, and footprints. Paleoecology: Study of the ecology and climate of the past, as revealed both by fossils and by other methods.

In short, paleontology is the study of what fossils tell us about the ecologies of the past, about evolution, and about our place, as humans, in the world. Paleontology incorporates knowledge from biology, geology, ecology, anthropology, archaeology, and even computer science to understand the processes that have led to the origination and eventual destruction of the different types of organisms since life arose.


Fossil Focus: Encephalized bipedal apes
paleontologyonline.com / by Holly M. Dunsworth

Humans would not have evolved if the ancestors of the African great apes had not. The ape fossil record begins 23 million years ago with the earliest putative apes, including Morotopithecus and Proconsul (Figure 1), from sites in East Africa, followed by many others throughout Africa, Europe and Asia. Although this record is fairly rich, it has done no better than DNA-based estimates at helping researchers to determine how living apes are related. Genetic studies estimate that gorillas split off from other apes about 9 million to 8 million years ago, and that the ancestors of bonobos and chimpanzees began evolving separately from the ancestors of humans 7 million to 6 million years ago.


Figure 1 – Right lateral (a) and front (b) views of the fossilized teeth and bones of the skull of the early ape Proconsul (museum catalogue no. KNM-RU 7290). Mary Leakey discovered this specimen, well-known for its remarkable preservation, on Rusinga Island, Kenya, in 1948. Images are not to scale with one another. Credit: Alan Walker.

Comparative anatomy, physiology, behaviour and genetics provide enough evidence for us to understand that humans are more closely related to chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) than to any other species, and vice versa. But the fossil record of hominins (species more closely related to humans than to chimps) preserves snapshots of the how the evolutionary path of our lineage differs from theirs. Unfortunately, the fossil record of chimpanzee and bonobo evolution is small enough to fit into a coat pocket, but the fossil evidence for human evolution is far greater: there are hundreds of specimens, including many nearly complete skeletons and many well-preserved skulls. Although the hominin fossil record is dominated by durable teeth — which reveal diet, age of death, pace of growth and much more — here we will focus, briefly, on the tales of two other significant human traits that are well documented in the hominin lineage: our big brains and our bipedal bodies.

Of course, humans are not the only animals to have extremely large brains for their body sizes (to be highly encephalized). Witness the octopus and the squid — members of the cephalopod class — and, among mammals, the toothed whales, or odontocetes. The African great apes also have large brains, but humans, as the sole surviving hominin, are considered to be the most encephalized. Nor are humans the only animals to walk habitually on two legs. Birds and many of their extinct dinosaur relatives are just some of the many bipeds that have roamed, and continue to roam, Earth. But although many primates, especially the African great apes, frequently walk on their hind limbs — particularly when carrying objects, while moving about the trees and during bouts of threatening or playing — humans are the only ones to be dedicated to this mode of locomotion.

The first five million years or so of the hominin fossil record (from about 7 million to 2 million years ago) are dominated by the gradual appearance of bipedal characteristics in the skeleton. It was not until the last 2 million years — by which point most of the skeleton, apart from the cranium (or top part of the skull), resembled that of a modern human — that encephalization took off.

Evolving bipedalism (Late MiocenePliocene, sub-Saharan Africa)

Compared with other apes — for example, gorillas (Figure 2), which climb and hang in trees and walk on all fours using their manual knuckles — the human skeleton’s anatomy reflects adaptations for upright walking and running. The human pelvis is modified so that the ilia (the blades) are bowl-shaped and curved around to the sides of the body, rearranging the muscles for balance during the single-support phase (i.e. when only one foot is on the ground) that dominates the time we spend walking. The spine is curved at the lumbar (lower back) and cervical (neck) regions, balancing our skeletons. Human legs are longer than our arms and long for our overall size compared to apes, helping to make us better travellers. Our hip joints are large and sturdy, because only two limbs bear our weight. Our knees are also large and reveal the angle of our femur (thigh bone), bringing the knee and the foot directly under our centre of gravity with every step. Our ankles and heels are rigid bony blocks, and the arches of our feet help to store and release energy with each stride. Our hallux (big toe) is not able to grasp like the thumb-like toe of many apes, but instead lines up with the other digits (all short toes) and plays a role in forcefully pushing off from the ground (‘toe-off’) at the end of each step during walking and running.


Figure 2 — Drawings of a human and gorilla skeleton. Humans did not evolve from the African great apes (gorillas, chimpanzees and bonobos), but the anatomies of our common ancestors are thought to be more like those apes than like us. The further back we go in the hominin fossil record, the less human-like and the more ape-like they appear. http://en.wikipedia.org/wiki/File:Primatenskelett-drawing.cjpg

The absolute best evidence for bipedal behaviour in the fossil record comes from footprints; they are direct impressions of that behaviour, requiring absolutely no inference from the shape of fossilized skeletons. And in Laetoli, Tanzania, there are wonderfully preserved 3.6-million-year-old tracks left by at least two bipedal hominins. They are not exactly like the prints that humans make today, but they lack an ape-like, divergent big toe and are not accompanied by any hand or knuckle prints.

At the time the tracks were laid down there is dental and bony fossil evidence in East Africa for Australopithecus afarensis. This is the species of the famous partial skeleton known as Lucy, discovered in the 1970s. Because A. afarensis skeletal morphology indicates that it walked upright, the Laetoli trackways are credited to the species. However, just whether A. afarensis walked upright all the time or only some of the time, and how much its bipedalism resembled modern human bipedalism, is still debated because A. afarensis did not have all the features that we associate with bipedalism in ourselves. This also goes for related australopiths discovered in South Africa, Australopithecus africanus and Australopithicus sediba. The australopith pelvis is not as bowl-shaped as ours; the legs are short and the arms relatively long; the toes are long and slightly curved; and the configuration of the tarsals, or foot bones, causes debate over whether the foot had an arch and whether australopiths tended to walk ‘pigeon-toed’. Making interpretation more difficult are new finds such as a foot from the site of Burtele in Ethiopia, which is near to and from around the same time as sites that produce A. afarensis fossils. The Burtele foot has some anatomy that suggests bipedalism, but also has an ape-like divergent hallux. It’s too much variation to include in a single species and, because of the hallux, cannot possibly belong to the hominins that left footprints at Laetoli. Despite these intriguing problems, it is clear that bipedalism, in whatever form it came, had hit its stride during Australopithecus times.

(Bones of Contention): For many palaeoanthropologists, the presence of bipedalism is the standard way to identify a hominin, meaning to decide that a fossil is a member of the human family tree, not another ape’s. This is the main reason that australopiths are labelled as hominins. But australopith species are known to have lived only from a little over 4 million years ago to roughly 2 million years ago, which does not go far enough back to match DNA-based estimates of when hominins diverged from chimps and bonobos, around 7 million to 6 million years ago. There are fossils older than the australopiths that look tantalizingly like hominins, but not completely. They belong to three genera: Sahelanthropus (from about 7 million years ago in Chad); Orrorin (from about 6 million years ago in Kenya); and Ardipithecus (from between 5.8 million and 4.4 million years ago in Ethiopia). Tooth shape and indications that they walked on two legs mean that all three of these genera have been placed at the base of the hominin tree by some researchers. However, other researchers disagree, in large part because of debate about how these animals moved. Much more is known for Ardipithecus than the other two genera. As predicted for an early hominin, its skeleton has so many primitive and/or non-human-like features that it is not completely clear whether it was bipedal, and also whether it was an ancestor to australopiths (although its teeth suggest that it was).

For the foreseeable future, there will be debate about these early hominins and their behaviour: whether or not they walked on two feet regularly; they were doing so using a non-modern skeleton, so it is difficult to tell exactly how their movement worked. Bipedalism does not require a modern human skeleton, as shown by the Laetoli prints. However, the only way that researchers can work out how hominin fossils moved is to look at the observed anatomy and behaviour of the one surviving bipedal hominin species: modern humans. The traits that we associate with bipedalism in our own muscles and skeletons appeared slowly over the first 5 million years of hominin evolution, so those 5 million years are best described as showing a slow shift to habitual bipedalism.

There seems to have been an ecological shift to accompany the change in locomotion. Evidence, particularly from the chemistry of tooth enamel, suggests that australopiths were starting to eat lots of grasses and related plants, whereas other apes eat mostly fruits, leaves and nuts. This shift in dietary ecology supports the idea that the australopiths or their ancestors had moved out of the trees to look for food on the ground, consistent with a modified take on the ‘savannah hypothesis’ in which, during the Pliocene epoch (5.3 million to 2.6 million years ago), hominins evolved under pressure to be able to find food in the relatively new grasslands of East and South Africa. Instead of terrestrial bipedalism originating with scavenging and hunting behaviours, as in the usual savannah hypothesis, perhaps it began with a mainly herbivorous phase.

Another traditional scenario, suggested by Charles Darwin, is that bipedalism arose to free the hands for making and using tools, carrying tools and food, and throwing objects while foraging or socializing. Unfortunately for this hypothesis, there are few tools preserved from 7 million to 2.5 million years ago. If we accept that Ardipithecus, Orrorin and Sahelanthropus are early hominins, then we must say that bipedalism originated in wooded environments because that is how their environments have been reconstructed. The first hominins could have lived in trees as much or even more than extant great apes do now, and evolved bipedal locomotion there.

Evolving encephalization (Pleistocene, Old World)

Since the late Pliocene — when the hominin locomotor anatomy began to be familiarly human — hominin brains have tripled in size. Given that it is impossible to re-run evolution to find out whether our extreme encephalization could have evolved if we had not first become bipedal, we are all but forced (why? other highly encephalized species are not bipedal) to assume that bipedalism was a prerequisite.

There are three main hypotheses to explain hominin encephalization. The first is a technological scenario. Non-human primates that make and use tools have the largest brains and the most complex behaviours. Once the forelimbs are no longer necessary for locomotion, as in hapitually bipedal hominins, they can be used for more complex technology, more regularly, which in turn selects for further encephalization. This hypothesis is supported by the emergence of the first encephalized hominins — Homo habilis, the earliest members of our own genus — roughly coinciding with the earliest fairly regular appearance of crude stone tools, starting around 2.5 million years ago. These tools have been dubbed the Oldowan tradition, after Olduvai Gorge in Tanzania, where they were first discovered.

The second scenario to explain encephalization is ecological. Again, primates with complex ecological behaviours tend to have large brains. Once hominin bodies committed to bipedalism, they were suited for scavenging and hunting animal prey. Predicted consequences of this shift are borne out in the fossil record for Homo erectus, a hominin with half or more of the modern-human brain size, which emerged about 1.8 million years ago. The skeleton of H. erectus approaches modern proportions and the hominin’s anatomy seems to be built for short bursts of speed and long-distance travel. The diet included high-quality animal protein and fat for feeding a larger brain. H. erectus had a body size similar to that of modern humans (with lots of diversity), and it is the first hominin found outside Africa. Almost as soon as it originated in Africa, H. erectus dispersed across the continent and into Europe, central Asia and southeast Asia. (Why? Because it could, thanks to the changes above)

Much of the evidence for the ecological scenario is rooted in the discovery in the 1980s of a well-preserved H. erectus skeleton in Nariokotome in Kenya (Figure 3). It is not clear how large a role meat played in our ancestors’ diets, because the record is biased toward preserving bones of devoured prey over remains of devoured vegetation. However, there is no denying that an ecological shift occurred in the early Pleistocene, with H. erectus developing a more diverse diet and habitat and becoming more skilled at hunting. That shift must have included new requirements of the brain. There are hints at sites in Africa that H. erectus was able to control fire during the early Pleistocene, but the first reliable evidence of fire use does not appear until 800,000 years ago at a H. erectus site in Israel. Even then, there is no preserved evidence for regular fire use until around 400,000 years ago, when H. erectus was largely gone (or evolved into more modern) and more modern hominins existed. Scavenging, hunting, control and use of fire for cooking, living in diverse habitats in diverse climates and increasingly complex stone-tool manufacture require a larger, more complex brain. (These behaviors are possible due to a more complex brain)


Figure 3 — Nearly complete skeleton of the Nariokotome Boy (also known as Turkana Boy; museum catalogue no. KNM-WT 15000). This juvenile Homo erectus was discovered on the western side of Lake Turkana, Kenya, and dates to around 1.5 million to 1.6 million years ago. Credit: Alan Walker.

The third major hypothesis for encephalization is social. As hominins became skilled hunters and gatherers, they relied more and more on cooperative foraging behaviours, and being able to navigate social networks across time and space became increasingly adaptive behaviour. Once complex speech and language arrived, there would be new demands on the brain, not only for these behaviours, but also for the new cultural, cooperative environment that language created. Brain size, and especially the ratio of brain to body size, reached modern proportions by 500,000 years ago, with ‘archaic’ or early Homo sapiens, so social selective pressures would have contributed both to reaching modern brain sizes and to maintaining it through to the emergence of modern Homo sapiens – represented by skeletons dating to 195,000 years ago at Omo in Ethiopia. The same social conditions might have led to encephalization among Neanderthals, Homo neanderthalensis, which lived roughly 300,000 to 30,000 years ago in Europe, the Middle East, and Eurasia. Neanderthal encephalization was comparable to ours and maybe slightly greater. There is an ongoing argument among researchers as to whether Neanderthals were a separate species, called Homo neanderthalensis, or a subspecies of Homo sapiens.

The technological, ecological and social pressures, requirements or demands could have worked both together and at different times throughout the Pleistocene epoch to the present and over many hominin generations. These evolutionary pressures would contribute to the more or less sustained reproductive success of hominins with slightly larger brains. And the fossil and archaeological records suggest that technology would have had the earliest effect, followed by the shift in ecology, and then sociality. These are some of the most mainstream hypotheses for encephalization and they implicitly or explicitly depend on bipedalism evolving before encephalization.

From bipedal ape to encephalized bipedal ape

We assume that some population of australopiths gave rise to the first members of the human genus, Homo. The earliest known Homo is australopith-like in anatomy but has a few differences, mainly its ever-so-slightly larger cranial capacity (a good proxy for brain size during life). Some researchers have argued that australopiths have marked encephalization, but others think that only early Homo had more encephalization than living apes. This debate will continue until more fossils are found that have indicators of both brain and body size for comparison. Until then, most researchers are comfortable beginning the brain-size story with Homo. It probably helps that the earliest stone tools on record and the earliest evidence for animal carcasses processed with those tools are found during the early Pleistocene, in early Homo times.

It is unclear when the hominin ecological shift to being stone-tool-making, meat-eating apes began. If the behaviour was common by H. erectus times, it should have started earlier. There is tantalizing evidence to suggest just this: the first known stone tools are from Gona in Ethiopia at about 2.6 million years ago, when only australopiths are thought to have been present. At 2.5 million years ago, when there were still just australopiths present, there are bones marked with cuts made by stone tools at nearby Bouri in Ethiopia. A few years ago, another site in Dikika, Ethiopia, dated to 3.4 million years ago (during A. afarensis times), produced what appear to be bones marked by stone-tool cuts. If this evidence is interpreted correctly, it is consistent with the dawn of an ecological shift leading up to the more conspicuous evidence with Homo erectus.

Considering the evolution of these two major traits from an energetic standpoint, bipedalism may have been a prerequisite for encephalization. Bipedal locomotion appears to expend less energy than walking terrestrially as a great ape and that freed-up energy could have been reallocated to brain growth. And, of course, with greater technological, ecological and social intelligence aiding human foragers the resulting increase in food quality and quantity provided the energy for growing a large hominin brain.  Pound for pound, brains are metabolically expensive so even something as seemingly straightforward as natural selection for a large intelligent brain must be a complex story.

Palaeoanthropologists continue to strive for better methods of understanding behaviour from bones and describing the anatomical, ecological and environmental contexts of the origins and evolution of bipedalism and encephalization. New fossil, archaeological and geological discoveries will be crucial for solving these puzzles in palaeoanthropology.

Suggested reading

Peer-reviewed articles about human and primate evolution.

All the articles published in Science about the discovery of Australopithecus sediba are here.

For comprehensive estimates of lineage splitting times, see Time Tree: The scale of life.

For introductory information about human evolution see http://humanorigins.si.edu/ & http://www.pbs.org/wgbh/evolution/humans/index.html