Tag: homo erectus

The Story of Human Evolution Now Challenged



Story of Human Evolution Challenged


Excerpt from newhistorian.com

The history of the evolution of early humans has been challenged.
Until now, one of the most dominant theories about our evolution claimed that our genus, Homo, had evolved from smaller early humans becoming taller, heavier and longer-legged. This process eventually resulted in Homo erectus, which was able to migrate out of Africa and colonise Eurasia.

Whilst we know that small-bodied H. erectus, averaging less than five feet tall and weighing under 50 kilograms, were living in southern Europe by 1.77 million years ago, the origin of the larger body size associated with modern humans has been elusive.

The paucity of knowledge about the origins of larger members of the Homo genus is primarily a result of a lack of evidence. Previous estimates of body size had been based on well-preserved specimens which were easy to assign a species to. Since these samples are rare and disparate in terms of both space and time, little is known about geographical and chronological variation in the body sizes of the early Homo.

A joint study between the Universities of Cambridge and Tübingen has shown that increases in body size occurred thousands of years after H. erectus left Africa; this growth in Homo body sizes primarily took place in the Koobi Fora region in modern Kenya.

“The evolution of larger bodies and longer legs can thus no longer be assumed to be the main driving factor behind the earliest excursions of our genus to Eurasia,” said Manuel Will, co-author of the study which has been published in the Journal of Human Evolution.

By using tiny fragments of fossil, the team were able to estimate our earliest ancestors’ height and body mass. Their findings, rather surprisingly, indicate a huge diversity in body size; this is particularly surprising as the wide variation we see in humans today was thought to be a relatively recent development.

“If someone asked you ‘are modern humans 6 foot tall and 70kg?’ you’d say ‘well some are, but many people aren’t,’ and what we’re starting to show is that this diversification happened really early in human evolution,” said Dr Jay Stock, co-author of the study.

Stock and Will are the first scientists in 20 years to compare the body size of humans from between 2.5 and 1.5 million years ago. They are also the first to use fragmentary fossils – many as small as toes, none longer than 5cm – to estimate body sizes.

By comparing measurements of fossils from sites in Kenya, Tanzania, South Africa and Georgia, the researchers have revealed substantial regional variation in the size of early humans. Groups who lived in South African caves, for example, were 4.8 feet tall on average. Some of the skeletons found in Kenya’s Koobi Fora region would have stood nearly 6 feet tall, a height comparable to the average height of modern British males.
“Basically every textbook on human evolution gives the perspective that one lineage of humans evolved larger bodies before spreading beyond Africa. But the evidence for this story about our origins and the dispersal out of Africa just no longer really fits,” said Stock.

It appears that Stock and Will have rewritten the history of the development of early humans; diversity has deep roots amongst the Homo genus.

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What our ancient ancestors found beautiful 50,000 years ago






Excerpt from news.discovery.com

The geode (above), described in the latest issue of Comptes Rendus Palevol, was found in the Cioarei-Boroşteni Cave, Romania. A Neanderthal had painted it with ochre.

"The Neanderthal man must have certainly attached an aesthetic importance to it, while its having been painted with ochre was an addition meant to confer symbolic value," said Marin Cârciumaru of Valahia University and colleagues.

The researchers also noted that "the geode was undoubtedly introduced into the cave by the Neanderthal," since they ruled out that it could have originated in the cave itself.

Was the geode used in rituals, or was it just a treasured object of beauty? Its precise meaning to the Neanderthal remains a mystery for now.




Based on archaeological finds, necklaces made out of Spondylus (a spiky, colorful mollusk) were all the rage. (Above)

This specimen has more of a reddish hue, but Michel Louis Séfériadès of CNRS notes that most are "a highly colored, very attractive purplish crimson." Séfériadès added that the shells were valued, early trade items and that they are now "found in the archaeological remains of settlements and cemeteries, in graves, and as isolated finds."

Some of the shells were made into jewelry, including necklaces and bracelets.

 

We sing about "five gold rings," but the rings would more likely have been ivory back in the day -- as in around 50,000 years ago, before ivory-producing animals were mostly hunted to extinction.
Early humans in northern regions, for example, made rings out of mammoth ivory. A Neanderthal site at Grotte du Renne, France yielded a carefully crafted ivory ring (above), as well as grooved and perforated "personal ornaments," according to archaeologist Paul Mellars of Cambridge University.



Charcoal (shown avove), ochre and other materials were applied to the face by early Homo sapiens as well as by other human subspecies. 

The ochre, used to paint the geode, mentioned earlier, was also used as makeup, hair dye, paint (to create rock and cave art), as well as to color garments.


Early humans used combs made out of shells and fish bones to both comb their hair and as personal decoration. (Above)

The shell from the Venus comb murex, a large predatory sea snail, is just one species that seems perfect for this purpose. Gibraltar Museum researchers Clive Finlayson and Kimberley Brown also found evidence that Neanderthals valued large, elaborate feathers, which the scientists suspect were worn by the individuals. 

Nearly all early cultures had coveted figurines holding probable symbolic value. Some of the earliest carved objects are known as "Venus" figurines. They present women with exaggerated sexual features. Their exact meaning remains unclear. (Above)

Pendants made of animal teeth were common and probably served many different functions, such as showing the hunter's success, offering symbolic protection, and just as fashion. 

Some of the funkiest-looking teeth were made into worn objects.
Animal teeth could be on a gift list dated to 540,000 years ago, and possibly earlier, as a recent study in the journal Nature found that a population of Homo erectus at Java, Indonesia, was collecting shark teeth and using them as tools and possibly as ornamentation.

 

The world's oldest known musical instrument is a bone flute (Above). While the earliest excavated flute dates to about 42,000 years ago, comparable flutes were probably made much earlier.

Flutes, like most of the items on this list, were not essential to survival, but yet they somehow contributed to the prehistoric peoples' quality of life.

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New prehistoric human discovered in Taiwan



human jaw fossil found in Taiwan
“Penghu 1,” the newly discovered human with large teeth, is another piece of critical evidence suggesting that other humans besides Homo sapiens lived in Asia from 200,000 to 10,000 years ago.


Excerpt from sciencerecorder.com


Paleontologists have identified the first known prehistoric human specimen from Taiwan, which may have been part of a species that lived alongside modern humans until as recently as 10,000 years ago.
“Penghu 1,” the newly discovered human with large teeth, is another piece of critical evidence suggesting that other humans besides Homo sapiens lived in Asia from 200,000 to 10,000 years ago.
Among the species that lived in Europe within that period were Neanderthals, Denisovans and Homo floresiensis The Penghu 1, which has been described in the most recent issue of Nature Communications, has added to that sizable list of humans that may have lived with and interbred with modern humans.

“The available evidence at least does not exclude the possibility that they survived until the appearance of Homo sapiens in the region, and it is tempting to speculate about their possible contact,” said the study’s co-author Yousuke Kaifu, an associate professor in the Department of Biological Sciences at The University of Tokyo, to Discovery News.
Kaifu, along with the paper’s lead author Chun-Hsiang Chang, and their team have studied the new human’s remains, primarily a jawbone that still contains big teeth. The jawbone was found by fishermen off the Taiwanese coast in the Penghu Channel. They then sold it to a local antique shop where it was found and bought by the collector Kun-Yu Tsai, who donated his collection to the National Museum of Natural Science in Taiwan. It then caught the eye of Chang, who works at the museum as a geologist.
Chang and his team now believe that the Penghu 1 could suggest a new species of human or at least a distinct regional group of Homo erectus. He suspects that the jawbone belonged to an elderly adult due to the worn state of the teeth. Unlike Homo floresiensis, the Penghu 1 grew to adult stature and lived on the Asian mainland.
“The associated faunal remains suggest that the area was a relatively open, wet woodland,” said Kaifu. “This is because of the presence of large-bodied mammals, such as elephants (Stegodon), horses and bear, but the fauna also included animals that prefer marshlands in a hot and humid climate, such as water buffaloes.”
All of these aspects would seem very attractive to modern humans, as well as the prehistoric humans they co-existed with. Although Penghu 1 is clearly not a modern human, its jaw bears many similarities to Homo erectus. Very little is known about human evolution in Asia, so this is a considerably welcome discovery, as fossils from much earlier periods discovered in China have offered valuable insights into what a Cretaceous ecosystem looked like. There are also many similarities between Penghu 1 and the Peking Man remains from Zhoukoudian, China, although the former appears to be much more primitive. It has also been compared to the archaic Homo heidelbergensis and also Denisovan remains.

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World’s Oldest Art Identified in Half-Million-Year-Old Zigzag

A jagged line etched on a fossil mussel shell may be the oldest evidence of geometric art.Photograph by Wim Lustenhouwer, VU University Amsterdam(Reuters) - It's a simple zigzag design scratched onto the surface of a freshwater mussel shell on t...

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Are Hobbits Real? Who are the Hobbits Discovered on the Island of Flores, Indonesia?

Archeological excavations at Liang Bua.


humanorigins.si.edu


A tiny hominin found on the island of Flores, Indonesia has shaken up the world of paleoanthropology. Human Origins scientist Matt Tocheri explains why.



The Island of Flores

Flores is one of many Wallacean islands, which lie east of Wallace's Line and west of Lydekker's Line.  Wallacean islands are interesting because they have rarely, if ever, been connected via land bridges to either the Asian continent to the west or the Greater Australian continent to the east.  This longstanding separation from the surrounding continents has severely limited the ability of animal species to disperse either into or away from the Wallacean islands.  Thus, on Flores there were only a small number of mammal and reptile species during the entire Pleistocene.  These included komodo dragons and other smaller monitor lizards, crocodiles, several species of Stegodon (an extinct close relative of modern elephants), giant tortoise, and several kinds of small, medium, and large-bodied rats.

Map showing the location of Flores relative to the Wallace Line and Lydekker's Line and the Pleistocene coastlines of the Asian and Greater Australian continents.
Map showing the location of Flores relative to the Wallace Line and Lydekker's Line and the Pleistocene coastlines of the Asian and Greater Australian continents.
During the 1950s and 60s, a Dutch priest named Father Theodor Verhoeven lived and worked on Flores at a Catholic Seminary.  Verhoeven had a keen interest in archeology and had studied it at university.  While living on Flores, he identified dozens of archeological sites and conducted excavations at many of these, including the now famous site of Liang Bua where the "hobbits" of human evolution were discovered (Homo floresiensis).  Verhoeven was the first to report and publish that stone tools were found in association with Stegodon remains in central Flores at several sites within the Soa Basin.  He even argued that Homo erectus from Java was likely behind making the stone tools found on Flores and may have reached the island around 750,000 years ago.  At the time, paleoanthropologists took little notice of Verhoeven's claims or if they did, they discounted them outright.

Father Verhoeven sitting near the site of one of his excavations on Flores at the Soa Basin during the 1960s. Image from Verhoeven, 1968.
Father Verhoeven sitting near the site of one of his excavations on Flores at the Soa Basin during the 1960s. Image from Verhoeven, 1968.

Almost thirty years later, an Indonesian-Dutch research team uncovered evidence at the Soa Basin which confirmed Verhoeven's original findings.  This team even went further by dating some of the stone tools and fossils using paleomagnetism (a method of determining the age of ancient sediments) and showed they were probably around 700,000 years old.  These new findings did not become widely known within the paleoanthropological community until additional sediments were dated using a different technique called zircon fission-track analysis.  Thus, by the late 1990s more scientists were beginning to accept the possibility that another human species (likely Homo erectus) had crossed the Wallace Line and reached Flores well before our own species, Homo sapiens, had evolved in Africa around 200,000 years ago.
In 2001, an Indonesian-Australian research team began excavations at a large limestone cave located in west central Flores.  This cave, known as Liang Bua (which means "cool cave"), was first excavated by Father Verhoeven in 1965.  Professor Raden Soejono, the leading archeologist in Indonesia, heard about Liang Bua from Verhoeven and conducted six different excavations there from the late 1970s until 1989.  All of this early work at Liang Bua only explored deposits that occurred within the first three meters of the cave floor.  These deposits are dated to within the last 10,000 years and contain considerable archeological and faunal evidence of modern human use of the cave, as well as skeletal remains of modern humans.  However, in 2001 the new goals were to excavate deeper into the cave's stratigraphy to explore if modern or pre-modern humans were using Liang Bua prior to 10,000 years ago.  In September of 2003, they got their answer.

 
The Discovery of Homo floresiensis
On Saturday, September 6, 2003, Indonesian archeologist Wahyu Saptomo was overseeing the excavation of Sector VII at Liang Bua.  Benyamin Tarus, one of the locally hired workers, was excavating the 2 x 2 meter square when all of a sudden the top of a skull began to reveal itself.  Six meters beneath the surface of the cave, Wahyu immediately joined Benyamin and the two of them slowly and carefully removed some more sediment from around the top of the skull.  Wahyu then asked Indonesian faunal expert Rokus Due Awe to inspect the excavated portion of the skull.  Rokus told Wahyu that the skull definitely belonged to a hominin and most likely that of a small child given the size of its braincase.  Two days later, the team returned to the site and Thomas Sutikna, the Indonesian archeologist in charge of the excavations, joined Wahyu at the bottom of the square.  After several days, enough of the cranium and mandible had been exposed for Rokus to realize that this was no small child; instead, all of its teeth were permanent meaning that this was a fully grown adult.  A few weeks later, the team had recovered the rest of this hominin's partial skeleton, the likes of which had never been discovered before.  Today, this specimen is referred to as LB1 (Liang Bua 1), and is the holotype specimen for the species Homo floresiensis.


Thomas Sutikna (blue hat) and Benyamin Tarus (white hat) at Liang Bua work to uncover the partial skeleton of Homo floresiensis in 2003.
Thomas Sutikna (blue hat) and Benyamin Tarus (white hat) at Liang Bua work to uncover the partial skeleton of Homo floresiensis in 2003.

At the time of the discovery, the Liang Bua Research Team included specialists in archeology, geochronology, and faunal identification, but there was no physical anthropologist.  Dr. Mike Morwood, the co-leader of the project, invited his colleague at the University of New England in Australia, Dr. Peter Brown, to lead the description and analysis of the skeletal remains.  Dr. Brown is an expert on cranial, mandibular, and dental anatomy of early and modern humans and he agreed to apply his expertise to the study of the new bones from Liang Bua.  This important scientific work resulted in the first descriptions of these skeletal remains in the journal Nature on October 28, 2004.  This work also gave the scientific name, Homo floresiensis, to the hominin species that is represented by the skeletal material from the Late Pleistocene sediments at Liang Bua. 

The holotype specimen of Homo floresiensis.
The holotype specimen of Homo floresiensis.

Just before the two Nature articles on Homo floresiensis were published in 2004, the Liang Bua Research Team uncovered additional skeletal material.  This included the arm bones of LB1, and several bones of another individual, LB6, including the mandible and other bones of the arm.  Drs. Morwood and Brown, and other Indonesian and Australian members of the Liang Bua Research Team, described and analyzed these new skeletal remains of Homo floresiensis and again published their results in Nature on October 13, 2005.
The skeletal evidence suggests that adults of this species had extremely small brains (400 cubic centimeters), stood only about 1 meter (3'6") tall, and weighed around 30 kg (66 lbs).  For their height, these individuals have large body masses, and in this regard appear more similar to earlier hominins like "Lucy" (Australopithecus afarensis) than they do to modern humans, including small and large-bodied people.  The proportions between the upper arm (humerus) and upper leg (femur) also appear more similar to those in Australopithecus and Homo habilis than those of modern humans.

Further Research

As additional postcranial material of Homo floresiensis was being recovered, Dr. Morwood contacted Dr. Susan Larson and Dr. William Jungers, of Stony Brook University Medical Center.  Drs. Larson and Jungers are experts on human evolutionary anatomy, particularly with regard to the functional morphology of the arms and legs.  Dr. Larson has shown that the shoulder of Homo floresiensis is more like that in Homo erectus rather than modern humans, and Dr. Jungers has demonstrated many anatomical features of the "hobbit" foot that are shared with African apes and early hominins like Australopithecus afarensis (e.g., "Lucy").  Dr. Morwood also invited hominin brain expert Dr. Dean Falk to analyze the endocast of Homo floresiensis.  Dr. Falk has identified several features in the "hobbit" brain that suggest neural reorganization despite its overall small size.  Additional research focused on the paleobiology and archeology of Homo floresiensis by Drs. Morwood, Brown, Larson, Jungers, Falk, their many Indonesian colleagues, and a large international network of scientific experts, was recently published in a special issue of Journal of Human Evolution (November 2009).  Discussions and summaries of some of the work included in that special issue will be presented on this web page over the coming weeks and months.   
In total, over a dozen scientific articles have been published based on analysis of the original skeletal remains of Homo floresiensis, and hundreds of scientific articles and news stories about Homo floresiensis have appeared in print or on the web during the past seven years since the partial skeleton of LB1 was discovered.  As excavations at Liang Bua and elsewhere on Flores continue, we will keep you up-to-date on the latest discoveries and scientific analyses of materials related to Homo floresiensis, the so-called "hobbits" of human evolution.  One of our Human Origins Program researchers, Dr. Matt Tocheri who has studied the wrist of Homo floresiensis, is looking forward to taking part in excavations this coming summer at Liang Bua and the Soa Basin.

The Liang Bua Excavation Team Leaders in 2009, from left to right, Dr. Kira Westaway, Jatmiko, Dr. Mike Morwood, Dr. Matt Tocheri, Thomas Sutikna, Wahyu Saptomo, Kompyang, Rok
The Liang Bua Excavation Team Leaders in 2009, from left to right, Dr. Kira Westaway, Jatmiko, Dr. Mike Morwood, Dr. Matt Tocheri, Thomas Sutikna, Wahyu Saptomo, Kompyang, Rokus Due Awe, and Sri Wasisto.

Bibliography
Argue, D., Donlon, D., Groves, C., Wright, R., 2006. Homo floresiensis: microcephalic, pygmoid, Australopithecus or Homo? Journal of Human Evolution 51, 360–374.
Argue, D., Morwood, M.J., Sutikna, T., Jatmiko, Saptomo, E.W., 2009. Homo floresiensis: a cladistic analysis. Journal of Human Evolution 57, 623–639.
Aziz, F., van den Bergh, G.D., Morwood, M.J., Hobbs, D.R., Collins, J., Jatmiko, Kurniawan, I., 2009. Excavations at Tangi Talo, central Flores, Indonesia. In: Aziz, F., Morwood, M.J., van den Bergh, G.D. (Eds.), Palaeontology and Archaeology of the Soa Basin, Central Flores, Indonesia. Indonesian Geological Survey Institute, Bandung, pp. 41–58.
Brown, P., Maeda, T., 2009. Liang Bua Homo floresiensis mandibles and mandibular teeth: a contribution to the comparative morphology of a new hominin species. Journal of Human Evolution 57 571–596.
Brown, P., Sutikna, T., Morwood, M.J., Soejono, R.P., Jatmiko, Saptomo, E.W., Rokus Awe Due, 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431, 1055–1061.
Falk, D., Hildebolt, C., Smith, K., Morwood, M.J., Sutikna, T., Brown, P., Jatmiko, Saptomo, E.W., Brunsden, B., Prior, F., 2005. The brain of LB1, Homo floresiensis. Science 308, 242–245.
Falk, D., Hildebolt, C., Smith, K., Jungers, W., Larson, S., Morwood, M., Sutikna, T., Jatmiko, Wahyu Saptomo, E., Prior, F., 2009a. The type specimen of Homo floresiensis (LB1) did not have Laron Syndrome. American Journal of Physical Anthropology 140, 52–63.
Falk, D., Hildebolt, C., Smith, K., Morwood, M.J., Sutikna, T., Jatmiko, Saptomo, E.W., Prior, F., 2009b. LB1’s virtual endocast, microcephaly and hominin brain evolution. Journal of Human Evolution 57, 597–607.
Jungers, W.L., Harcourt-Smith, W.E.H., Wunderlich, R.E., Tocheri, M.W., Larson, S.G., Sutikna, T., Rhokus Awe Due, Morwood, M.J., 2009a. The foot of Homo floresiensis. Nature 459, 81–84.
Jungers, W.L., Larson, S.G., Harcourt-Smith, W., Morwood, M.J., Sutikna, T., Rokhus Due Awe, Djubiantono, T., 2009b. Descriptions of the lower limb skeleton of Homo floresiensis. Journal of Human Evolution 57, 538–554.
Larson, S.G., Jungers,W., Tocheri, M.W., Orr, C.M., Morwood, M.J., Sutikna, T., Rokhus Due Awe, Djubiantono, T., 2009. Descriptions of the upper limb skeleton of Homo floresiensis. Journal of Human Evolution 57, 555–570.
Morwood, M.J., van Oosterzee, P., 2007. The Discovery of the Hobbit: The Scientific Breakthrough that Changed the Face of Human History. Random House, Sydney, Australia.
Morwood, M.J., Brown, P., Sutikna, T., Jatmiko, Saptomo, E.W., Westaway, K.E., Roberts, R.G., Rokus Awe Due, Maeda, T., Wasisto, S., Djubiantono, T., 2005. Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia. Nature 437, 1012–1017.
Morwood, M.J., O’Sullivan, P., Aziz, F., Raza, A., 1998. Fission track age of stone tools and fossils on the east Indonesian island of Flores. Nature 392, 173–176.
Morwood, M.J., Soejono, R.P., Roberts, R.G., Sutikna, T., Turney, C.S.M.,Westaway, K.E., Rink, W.J., Zhao, J.-x., van den Bergh, G.D., Rokus Awe Due, Hobbs, D.R., Moore, M.W., Bird, M.I., Fifield, L.K., 2004. Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature 431, 1087–1091.
Morwood, M.J., Sutikna, T., Saptomo, E.W., Jatmiko, Hobbs, D.R., Westaway, K.E., 2009. Preface: research at Liang Bua, Flores, Indonesia. Journal of Human Evolution 57, 437–449.
Sondaar, P.Y., van den Bergh, G.D., Mubroto, B., Aziz, F., de Vos, J., Batu Unkap, L., 1994. Middle Pleistocene faunal turnover and colonization of Flores (Indonesia) by Homo erectus. Comptes Rendus de l’Academie des Sciences 320, 1255–1262.
Tocheri, M.W., Caley, M., Orr, C.M., Larson, S.G., Sutikna, T., Jatmiko, Saptomo, E.W., Rokus Awe Due, Djubiantono, T., Morwood, M.J., Jungers, W.L., 2007. The primitive wrist of Homo floresiensis and its implications for hominin evolution. Science 317, 1743–1745.
van den Bergh, G.D., Meijer, H.J.M., Rokhus Due Awe, Morwood, M.J., Szabo´ , K., van den Hoek Ostende, L.W., Sutikna, T., Saptomo, E.W., Piper, P.J., Dobney, K.M., 2009. The Liang Bua faunal remains: a 95 k.yr. sequence from Flores, East Indonesia. Journal of Human Evolution 57, 527–537.
van den Bergh, G.D., Mubroto, B., Sondaar, P.Y., de Vos, J., 1996. Did Homo erectus reach the island of Flores? Indo-Pacific Prehistory Association Bulletin (Chiang Mai Papers) 14, 27–36.
Verhoeven, T., 1953. Eine Mikrolithenkultur in Mittel- und West-Flores. Anthropos 48, 597–612.
Verhoeven, T., 1958. Pleistozane funde in Flores. Anthropos 53, 264–265.
Verhoeven, T. 1968. Pleistozane funde auf Flores, Timor and Sumba. In: Geburtstag von P.W. Schmidt, (Ed.), Anthropica, Gedenkschrift zum 100. Studia Instituti Anthropos 21, St Augustin bei Bonn, pp. 393–403.

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Does the discovery of 1.77-million-year-old skeletons rewrite history? ~ Video

Dr Lordkipanidze and colleagues The latest discoveries the 1.77-million-year-old skeletons of three adults and a teenager have legs and feet adapted for long-distance walking and running, similar to those of modern humans, but have hands and arms ...

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Mysteries of the Early Human Ancestors #1 ~ Why did we grow large brains?

Human brains are about three times as large as those of our early australopithecines ancestors that lived 4 million to 2 million years ago, and for years, scientists have wondered how our brains got so big. A new study suggests social competition could be behind the increase in brain size. Credit NIH, NADA

livescience.com

There are many ways to try to explain why human brains today are so big compared to those of early humans, but the major cause may be social competition, new research suggests. 

But with several competing ideas, the issue remains a matter of debate. 

Compared to almost all other animals, human brains are larger as a percentage of body weight. And since the emergence of the first species in our Homo genus (Homo habilis) about 2 million years ago, the human brain has doubled in size. And when compared to earlier ancestors, such as australopithecines that lived 4 million to 2 million years ago, our brains are three times as large. For years, scientists have wondered what could account for this increase.

The three major hypotheses have focused on climate change, the demands of ecology, and social competition. A new statistical analysis of data on 175 fossil skulls supports the latter hypothesis. 

Behind the hypotheses

The climate idea proposes that dealing with unpredictable weather and major climate shifts may have increased the ability of our ancestors to think ahead and prepare for these environmental changes, which in turn led to a larger, more cognitively adept brain.
The ecology hypothesis states that, as our ancestors migrated away from the equator, they encountered environmental changes, such as less food and other resources. "So you have to be a little bit more clever to figure it out," said David Geary, a professor from the University of Missouri. Also, less parasite exposure could have played a role in the makings of a bigger brain. When your body combats parasites, it cranks up its immune system, which uses up calories that could have gone to boost brain development. Since there are fewer parasites farther away from the equator, migrating north or south could have meant that our predecessors had more opportunity to grow a larger brain because their bodies were not fighting off as many pathogens.


Finally, other researchers think that social competition for scarce resources influenced brain size. As populations grow, more people are contesting for the same number of resources, the thinking goes. Those with a higher social status, who are "a little bit smarter than other folks" will have more access to food and other goods, and their offspring will have a higher chance of survival, Geary said.


Those who are not as socially adept will die off, pushing up the average social "fitness" of the group. "It's that type of process, that competition within a species, for status, for control of resources, that cycles over and over again through multiple generations, that is a process that could easily explain a very, very rapid increase in brain size," Geary said.

Weighing the options

To examine which hypothesis is more likely, Geary and graduate student Drew Bailey analyzed data from 175 skull fossils — from humans and our ancestors — that date back to sometime between 10,000 ago and 2 million years ago.


The team looked at multiple factors, including how old the fossils were, where they were found, what the temperature was and how much the temperature varied at the time the Homo species lived, and the level of parasites in the area. They also looked at the population density of the region in order to measure social competition, "assuming that the more fossils you find in a particular area at a particular time, the more likely the population was larger," Geary said.


They then used a statistical analysis to test all of the variables at once to see how well they predicted brain size. "By far the best predictor was population density," Geary said. "And in fact, it seemed that there was very little change in brain size across our sample of fossil skulls until we hit a certain population size. Once that population density was hit, there was a very quick increase in brain size," he said.


Looking at all the variables together allowed the researchers to "separate out which variables are really important and which variables may be correlated for other reasons," added Geary. While the climate variables were still significant, their importance was much lower than that of population density, he said. The results were published in the March 2009 issue of the journal Human Nature.


Questions linger

The social competition hypothesis "sounds good," said Ralph Holloway, an anthropologist at Columbia University, who studies human brain evolution. But, he adds: "How would you ever go about really testing that with hard data?" 

He points out that the sparse cranium data "doesn’t tell you anything about the differences in populations for Homo erectus, or the differences in populations of Neanderthals." For example, the number of Homo erectus crania that have been found in Africa, Asia, Indonesia and parts of Europe is fewer than 25, and represent the population over hundreds of thousands of years, he said. 

"You can't even know the variation within a group let alone be certain of differences between groups," Holloway said. Larger skulls would be considered successful, but "how would you be able to show that these were in competition?" 

However, Holloway is supportive of the research. "I think these are great ideas that really should be pursued a little bit more," he said. 

Alternative hypotheses

Holloway has another hypothesis for how our brains got so big. He thinks that perhaps increased gestation time in the womb or increased dependency time of children on adults could have a played role. The longer gestation or dependency time "would have required more social cooperation and cognitive sophistication on the part of the parents," he said. Males and females would have needed to differentiate their social roles in a complementary way to help nurture the child. The higher level of cognition needed to perform these tasks could have led to an increase in brain size.


Still other hypotheses look at diet as a factor. Some researchers think that diets high in fish and shellfish could have provided our ancestors with the proper nutrients they needed to grow a big brain.
And another idea is that a decreased rate of cell death may have allowed more brain neurons to be synthesized, leading to bigger noggins. 

Ultimately, no theory can be absolutely proven, and the scant fossil record makes it hard to test hypotheses. "If you calculate a generation as, let's say, 20 years, and you know that any group has to have a minimal breeding size, then the number of fossils that we have that demonstrates hominid evolution is something like 0.000001 percent," Holloway said. "So frankly, I mean, all hypotheses look good."

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Evolution Versus Creation ~ Blowing the lid off the missing link Homo Erectus discovery!

Java Man or Homo ErectusTo set the table for this short video snippet of a lecture given by John Harris, transitional fossils are alleged fossil discoveries of early man that link present day humans to one or more primitive species. The term missing li...

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