Sunday, July 5, 2015

What Are Mitochondria?

Mitochondria are specialized structures unique to the cells of animals, plants and fungi. They serve as batteries, powering various functions of the cell and the organism as a whole. Though mitochondria are an integral part of the cell, evidence shows that they evolved from primitive bacteria. 

Occurrence

All living organisms are built with one fundamental brick: the cell. In some cases, a single cell constitutes an entire organism. Cells contain genetic material (DNA and RNA), and they carry out essential functions, such as metabolism and protein synthesis. Cells are also capable of self-replicating. However, the level of organization varies within the cells of different organisms. Based on these differences, organisms are divided into two groups: eukaryotes and prokaryotes. 

Plants, animals and fungi are all eukaryotes and have highly ordered cells. Their genetic material is packaged into a central nucleus. They also have specialized cellular components called organelles, each of which executes a specific task. Organelles such as the mitochondria, the rough endoplasmic reticulum and the golgi serve respectively to generate energy, synthesize proteins and package proteins for transport to different parts of the cell and beyond. The nucleus, as well as most eukaryotic organelles, is bound by membranes that regulate the entry and exit of proteins, enzymes and other cellular material to and from the organelle.

Prokaryotes, on the other hand, are single-celled organisms such as bacteria and archaea. Prokaryotic cells are less structured than eukaryotic cells. They have no nucleus; instead their genetic material is free-floating within the cell. They also lack the many membrane-bound organelles found in eukaryotic cells. Thus, prokaryotes have no mitochondria. 

Structure

In a 1981 review of the history of mitochondria in the Journal of Cell Biology, authors Lars Ernster and Gottfried Schatz note that the first true observation of mitochondria was by Richard Altmann in 1890. While Altmann called them “bioblasts,” their current, visually descriptive name was given by Carl Benda in 1898, based on his observations of developing sperm. “Mitochondria” derives from two Greek words: “mitos” meaning thread, and “chondros” meaning granule. As described by Karen Hales, a professor of biology at Davidson College, in Nature Education, these organelles are dynamic, and constantly fuse together to form chains, and then break apart. 

Individual mitochondria are capsule shaped, with an outer membrane and an undulating inner membrane, which resembles protruding fingers. These membranous pleats are called cristae, and serve to increase the overall surface area of the membrane. When compared to cristae, the outer membrane is more porous and is less selective about which materials it lets in. The matrix is the central portion of the organelle and is surrounded by cristae. It contains enzymes and DNA. Mitochondria are unlike most organelles (with an exception of plant chloroplasts) in that they have their own set of DNA and genes that encode proteins.

Plant mitochondria were first observed by Friedrich Meves in 1904, as mentioned by Ernster and Schatz (Journal of Cell Biology, 1981). While plant and animal mitochondria do not differ in their basic structure, Dan Sloan, an assistant professor at the University of Colorado said, their genomes are quite different. They vary in size and structure.

According to Sloan, the genomes of most flowering plants are about 100,000 base pairs in size, and can be as large as 10 million base pairs. In contrast, mammalian genomes are about 15,000 to 16,000 base pairs in size. Moreover, while the animal mitochondrial genome has a simple circular configuration, Sloan said that the plant mitochondrial genome, though depicted as circular, could take on alternate forms. “Their actual structure in vivo [within the plant] is not well understood. They might be complex branched molecules,” he said. 

Function

The main function of mitochondria is to metabolize or break down carbohydrates and fatty acids in order to generate energy. Eukaryotic cells use energy in the form of a chemical molecule called ATP (adenosine triphosphate). 

ATP generation occurs within the mitochondrial matrix, though the initial steps of carbohydrate (glucose) metabolism occur outside the organelle. According to Geoffrey Cooper in “The Cell: A Molecular Approach 2nd Ed” (Sinauer Associates, 2000), glucose is first converted into pyruvate and then transported into the matrix. Fatty acids on the other hand, enter the mitochondria as is. 

ATP is produced through the course of three linked steps. First, using enzymes present in the matrix, pyruvate and fatty acids are converted into a molecule known as acetyl-CoA.  This then becomes the starting material for a second chemical reaction known as the citric acid cycle or Krebs Cycle. This step produces plenty of carbon dioxide and two additional molecules, NADH and FADH2, which are rich in electrons. The two molecules move to the inner mitochondrial membrane and begin the third step: oxidative phosphorylation. In this last chemical reaction, NADH and FADH2 donate their electrons to oxygen, which leads to conditions suitable for the formation of ATP. 

A secondary function of mitochondria is to synthesize proteins for their own use. They work independently, and execute the transcription of DNA to RNA, and translation of RNA to amino acids (the building blocks of protein), without using any components of the cell. However, here too, there are differences within eukaryotes. The sequence of three DNA nucleotides U-A-G (uracil-adenine-guanine) is an instruction for translation to stop in the eukaryotic nucleus. 

According to the authors of “Molecular Cell Biology 4th Ed” (W.H. Freeman, 2000), while this sequence also stops translation in plant mitochondria, it encodes the amino acid tryptophan in the mitochondria of mammals, fruit flies and yeast. In addition, RNA transcripts that arise from mitochondrial genes are processed differently in plants than in animals. “Lots of modifications have to occur in plant mitochondria for those genes to be functional,” Sloan told LiveScience. For example, in plants, the individual nucleotides of RNA transcripts are edited before translation or protein synthesis takes place. Also, introns, or portions of mitochondrial RNA that do not carry instructions for protein synthesis, are spliced out. 

Origins of mitochondria: The Endosymbiont Theory

In her 1967 paper, “On the Origins of Mitosing Cells,” published in the Journal of Theoretical Biology, scientist Lynn Margulis proposed a theory to explain how eukaryotic cells along with their organelles were formed. She suggested that mitochondria and plant chloroplasts were once free-living prokaryotic cells that were swallowed up by a primitive eukaryotic host cell. 

Margulis’ hypothesis is now known as the “endosymbiont theory.” Dennis Searcy, emeritus professor at University of Massachusetts Amherst, explained it as follows: “Two cells began to live together, exchanging some sort of substrate or metabolite [product of metabolism, like ATP]. The association became mandatory, so that now, the host cell cannot live separately.” 

Even at the time that Margulis proposed it, versions of the endosymbiont theory were already in existence, some dating back to 1910 and 1915. “Although these ideas are not new, in this paper they have been synthesized in such a way as to be consistent with recentdata on the biochemistry and cytology of subcellular organelles,” she wrote in her paper. According to a 2012 article on mitochondrial evolution by Michael Gray in the journal Cold Spring Harbor Perspectives in Biology, Margulis based her hypothesis on two key pieces of evidence. First, mitochondria have their own DNA. Second, the organelles are capable of translating the messages encoded in their genes to proteins, without using any of the resources of the eukaryotic cell.  

Genome sequencing and analyses of mitochondrial DNA have established that Margulis was correct about the origins of mitochondria. The lineage of the organelle has been traced back to a primitive bacterial ancestor known as alphaproteobacteria (α-proteobacteria).

Despite the confirmation of the mitochondria’s bacterial heritage, the endosymbiont theory continues to be researched. “One of the biggest questions right now is, 'Who is the host cell?'” Sloan told LiveScience. As Gray noted in his article, the questions that linger are whether mitochondria originated after the eukaryotic cell arose (as hypothesized in the endosymbiont theory) or whether mitochondria and host cell emerged together, at the same time. 
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Reference:

Vidyasagar, Aparna. 2015. “What Are Mitochondria?”. Live Science. Posted: April 30, 2015. Available online: http://www.livescience.com/50679-mitochondria.html

Saturday, July 4, 2015

Not much size difference between male and female Australopithecines

Lucy and other members of the early hominid species Australopithecus afarensis probably were similar to humans in the size difference between males and females, according to researchers from Penn State and Kent State University.

"Previous convention in the field was that there were high levels of dimorphism in the Australopithecus afarensis population," said Philip Reno, assistant professor of anthropology, Penn State. "Males were thought to be much larger than females." Sexual dimorphism refers to differences between males and females of a species. These can show up, for example, in body size and weight or in the size of the canine teeth. For Australopithecines, canines of males and females are about the same size, but it was assumed their body sizes differed. Other primates have varying degrees of sexual dimorphism. Gorillas are highly dimorphic, with males weighing as much as 200 pounds more than females. Chimpanzees are only moderately sexually dimorphic with males weighing about 18 pounds more than females on average. Humans are moderately sexually dimorphic. Previously, researchers assumed that A. afarensis was similar to or even more dimorphic than gorillas in sexual size differences.

Lucy is probably the most famous example of A. afarensis, a supposed female who measures 3.5 feet in height. Also often used as an example of this species is A.L. 128/129, another small specimen assumed to be female. However, A. afarensis existed long before brains in the human line became large enough to require the alteration in the pelvic structure that both allows for large-headed baby births and easy identification of female specimens. "There is no reason why Lucy, if female, would have the wide notched pelvic bone of a human female," said Reno. "We can't really sex Australopithecines."

While Lucy may not be female, she is the earliest discovered and most well preserved example of A. afarensis and so has been used as a model for the study of other specimens. Recently, another reasonably intact A. Afarensis, Kadanuumuu, was uncovered and he stood 5 to 5.5 feet tall. Reno and C. Owen Lovejoy, distinguished professor of human evolutionary studies, Kent State, developed the Template Method to compare different skeletons and determine the range and dimorphism of A. Afarensis. They report their results in today's (Apr. 28) issue of PeerJ.

The pair used both Lucy and Kadanuumuu as templates for the method, which compares similar parts of the skeleton from partial remains to the nearly complete remains of the template. For example, the researchers compared the size of 41 specimens from different parts of the skeleton to that of Lucy. By determining the ratio of these specimens to Lucy, they could then calculate the relative size of partial bones from incomplete skeletons and better determine the size variation in the species.

Another method of determining sexual dimorphism is the Geometric Mean Method, which uses 11 characteristics to estimate size. Unfortunately, in this method, because Lucy is so complete a skeleton, she supplies seven or eight of the metrics; A.L. 128/129 supplies an additional three. So two very small individuals supply ten of the eleven metrics.

"In essence, Lucy is counted multiple times in the Geometric Mean Method, which gives her a skewed impact on the size of individuals," said Reno. "In our method, Lucy is weighted only once. The range shows intermediate moderate levels of sexual dimorphism, A. afarensis is within the human dimorphic range."

Another problem in comparing various A. afarensis skeletons is that except for those found in A.L. 333—a geologically contemporaneous group—individuals could be 10 thousand to 100 thousand years apart in age. During that time, the overall size of the species could have changed. Neither method can accommodate this potential time warp, but the researchers acknowledge that the time range is another variable that must be considered. Because Lucy was the first discovered specimen, it was easy to assume that she was a typical size specimen, but it now appears that Lucy is at the lower edge of A. afarensis size and that Kadanuumuu may be an outlier at the upper edge of the range with many intermediate sized specimens between the two, according to Reno.
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Reference:

Phys.org. 2015. “Not much size difference between male and female Australopithecines”. Phys.org. Posted: April 28, 2015. Available online: http://phys.org/news/2015-04-size-difference-male-female-australopithecines.html

Ancient archeological mystery solved: Cooling temps led to farming disaster, collapse of civilization

Climate change may be responsible for the abrupt collapse of civilization on the fringes of the Tibetan Plateau around 2000 B.C.

WSU archaeologist Jade D'Alpoim Guedes and an international team of researchers found that cooling global temperatures at the end of the Holocene Climatic Optimum, a 4,000 year period of warm weather, would have made it impossible for ancient people on the Tibetan Plateau to cultivate millet, their primary food source.

Guedes' team's research recently was published online in theProceedings of the National Academy of Sciences. Her results provide the first convincing explanation for why the area's original inhabitants either left or so abruptly changed their lifestyles.

They also help explain the success of farmers who practiced wheat and barley agriculture in the region 300 years later.

Unlike millet, wheat and barley have high frost tolerance and a low heat requirement, making them ideally suited for the high altitudes and cold weather of eastern Tibet. Guedes argues this made the two crops an important facet of subsistence immediately after their introduction around 1700 B.C.

"Wheat and barley came in at the opportune moment, right when millets were losing their ability to be grown on the Tibetan Plateau," Guedes said. "It was a really exciting pattern to notice. The introduction of wheat and barley really enabled Tibetan culture to take the form it has today, and their unique growth patterns may have played a crucial rule in the spread of these crops as staples across the vast region of East Asia."

One offshoot of the research: The ancient millet seeds that fell out of cultivation on the Tibetan Plateau as the climate got colder might soon be useful again as the climate warms up.

"Right now, these millets have almost become forgotten crops," Guedes said. "But due to their heat tolerance and high nutritional value, they may be once again be useful resources for a warmer future."

An archaeological enigma

At Ashaonao, Haimenkou, and other archeological sites in the Tibetan highlands, researchers for years had noticed a growing trend. An abundance of ancient wheat and barley seeds found at the sites suggested the crops rapidly replaced millet as the staple food source of the region during the second millennium BCE.

The findings were puzzling considering that the scientific consensus of the time was the region's climate would have actually favored millet, due to its shorter growing season, over wheat or barley.

The conundrum intrigued Guedes so she dove into the agronomy literature to investigate. She found agronomists tended to use a different measurement than archaeologists to determine whether crops can grow in cold, high altitude environments like the Tibetan Plateau. They used total growing degree days or the accumulated amount of heat plants need over their lifetime rather than the length of a growing season.

"My colleagues and I created a new model based off what we found in the literature," Guedes said. "It revealed that global cooling would have made it impossible to grow millet in the Eastern Tibetan Highlands at this time but would have been amenable to growing wheat and barley. Our work turned over previous assumptions and explained why millet is no longer a staple crop in the area after 2000 BCE."

Guedes' work points to climate cooling as the culprit behind the collapse of early civilization on the Tibetan Plateau. Ironically, the region is today one of the areas experiencing the most rapid climate warming on the planet. There are some areas in the southeastern plateau where temperatures are 6 degrees Celsius higher than they were 200 years ago.

Rapid temperature increase is making it difficult for the region's inhabitants to raise and breed yaks, a staple form of subsistence in the central Asian highlands, and grow cold weather crops, once again endangering their survival.

"So now we have a complete reversal and climate warming is having a big impact on the livelihood of smaller farmers on the Tibetan Plateau," Guedes said.
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Reference:

Science Daily. 2015. “Ancient archeological mystery solved: Cooling temps led to farming disaster, collapse of civilization”. Science Daily. Posted: April 29, 2015. Available online: http://www.sciencedaily.com/releases/2015/04/150429090110.htm

Friday, July 3, 2015

Early Urban Planning: Ancient Mayan City Built on Grid

An ancient Mayan city followed a unique grid pattern, providing evidence of a powerful ruler, archaeologists working at Nixtun-Ch'ich' in Petén, Guatemala, have found.

The city, which contains flat-topped pyramids, was in use between roughly 600 B.C. and 300 B.C., a time when the first cities were being constructed in the area. No other city from the Maya world was planned using this grid design, researchers say. This city was "organized in a way we haven't seen in other places," said Timothy Pugh, a professor at Queens College in New York.

"It's a top-down organization," Pugh said. "Some sort of really, really, powerful ruler had to put this together."

The ancient Mexican city of Teotihuacan also used a grid system. But that city is not considered to be Mayan, and so far archaeologists have found no connections between it and the one at Nixtun-Ch'ich', Pugh said.  People living in the area have known of the Nixtun-Ch'ich' site for a long time. Pugh started research on it in 1995 and has been concentrating on Mayan remains that date to a much later time period,long after the early city was abandoned. However, in the process of studying these later remains, his team has been able to map the early city and even excavate a bit of it. 

Ceremonial route

From the mapping and excavations, Pugh can tell that the city's main ceremonial route runs in an east-west line only 3 degrees off of true east. "You get about 15 buildings in an exact straight line — that's the main ceremonial area," he said. These 15 buildings included flat-topped pyramids that would have risen up to almost 100 feet (30 meters) high. Visitors would have climbed a series of steps to reach the temple structure at the top of each of these pyramids.

At the end of the ceremonial way, on the eastern edge of the city, is a "triadic" structure or group, which consists of pyramids and buildings that were constructed facing each other on a platform. Structures like this triadic group (the name comes from the three main pyramids or buildings in the group), have been found in other early Mayan cities.

The residential areas of the city were built to the north and south of the ceremonial route and were also packed into the city's grid design, Pugh said.

From the excavations, archaeologists can tell that many of the city's structures were decorated with shiny white plaster. "It was probably a very shiny city," Pugh said.

The city's orientation, facing almost directly east, would have helped people follow the movements of the sun, something that may have been of importance to their religion.

A wall made of earth and stone also protectedthe city, suggesting defense was also a concern of these Mayans.

Were the people miserable?

While the city was a sight to behold, its people might not have been happy with it, Pugh said.

"Most Mayan cities are nicely spread out. They have roads just like this, but they're not gridded," said Pugh, noting that in other Mayan cities, "the space is more open and less controlled."

Cities in early Renaissance Europe that adopted rigid designs were often unpleasant places for their residents to live, Pugh said. It's "very possible" that the residents of this early Mayan city "didn't really enjoy living in such a controlled environment," Pugh said.

Preserving the city

Archaeologists said they are thankful to the cattle ranchers who own the land the site is on and are protecting it against looters, Pugh said.

This location is one of the few Mayan sites in the area that hasn't been looted, and that's because the ranchers are "really protective, and they don't want people messing with the Maya ruins," Pugh said.

Additionally, the ranchers use a type of quick-growing grass, which, in addition to helping feed cattle, also protects the site from erosion, helping preserve it.

Pugh's team presented their research recently at the Society for American Archaeology's Annual Meeting, in San Francisco.
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Reference:

Jarus, Owen. 2015. “Early Urban Planning: Ancient Mayan City Built on Grid”. Live Science. Posted: April 29, 2015. Available online: http://www.livescience.com/50659-early-mayan-city-mapped.html

Thursday, July 2, 2015

Paleo-Eskimos and Neo-Eskimos Migrated from Alaska's North Slope

New genetic testing of Iñupiat people currently living in Alaska's North Slope has determined the migration patterns and ancestral pool of the people who populated the North American Arctic over the last 5,000 years and found that all mitochondrial DNA haplogroups previously found in the ancient remains of Neo- and Paleo-Eskimos and living Inuit peoples from across the North American Arctic were found within the people living in North Slope villages.

The findings support the archaeological model that the "peopling of the eastern Arctic" began in the North Slope, in an eastward migration from Alaska to Greenland. It also provides new evidence to support the hypothesis that there were two major migrations to the east from the North Slope at two different times in history. There hadn't been a clear biological link found in the DNA of the Paleo-Eskimos, the first people to spread from Alaska into the eastern North American arctic, and the DNA of Neo-Eskimos, a more technologically sophisticated group that later spread very quickly from Alaska and the Bering Strait region to Greenland and seemed to replace the Paleo-Eskimo.

"This is the first evidence that genetically ties all of the Iñupiat and Inuit populations from Alaska, Canada and Greenland back to the Alaskan North Slope," said Northwestern's M. Geoffrey Hayes, senior author of the new study in the American Journal of Physical Anthropology. "Our study suggests that the Alaskan North Slope serves as the homeland for both of those groups, during two different migrations. We found DNA haplogroups of both ancient Paleo-Eskimos and Neo-Eskimos in Iñupiat people living in the North Slope today."

At the request of Iñupiat elders from Barrow, Alaska, who are interested in using scientific methods to learn more about the history of their people, Hayes and a team of scientists extracted DNA from saliva samples given by 151 volunteers living in eight different North Slope communities. This is the first genetic study of modern-day Iñupiat people. The authors sequenced and analyzed only mitochondrial DNA. Mitochondrial DNA is passed down from mother to child, with few changes from generation to generation. 98 percent of the maternal linages in this group were of Arctic descent. The scientists found all known Arctic-specific haplogroups present in these North Slope communities. The haplogroups are: A2a, A2b, D4b1a and D2.

D2 is the known haplogroup of ancient Paleo-Eskimos. Until this study D2 had only been found in the remains of ancient Paleo-Eskimos. D4b1a is a known haplogroup of the ancient Neo-Eskimos, the much more technologically sophisticated group that came after the Paleo-Eskimos and seemed to replace them and populate a large part of the Arctic in a short amount of time.

"We think the presence of these two haplotypes in villages of the North Slope means that the Paleo-Eskimos and the Neo-Eskimos were both ancestors of the contemporary Iñupiat people," said Jennifer A. Raff, first author of the study and a post-doctoral fellow in Hayes' lab at the Feinberg School when the research was being done. "We will be exploring these connections in the future with additional genetic markers."

Another haplogroup that surfaced in this study was C4. This is typically only seen in Native Americans much farther south. Its geographic distribution suggests that it might have been one of the haplogroups carried by the earliest peoples to enter the Americas. The researchers think it could be seen in the North Slope because of recent marriages between Athapascan and Iñupiat families or because it is a remnant of a much more ancient contact between these groups. Additional authors of this study are Margarita Rzhetskaya of Northwestern and Justin Tackney of the University of Utah. The National Science Foundation's Office of Polar Programs funded the study (grant numbers OPP-0732846 and OPP-0732857).
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Reference:

Science 2.0. 2015. “Paleo-Eskimos and Neo-Eskimos Migrated from Alaska's North Slope”. Science 2.0. Posted: April 29, 2015. Available online: http://www.science20.com/news_articles/paleoeskimos_and_neoeskimos_migrated_from_alaskas_north_slope-155179

Wednesday, July 1, 2015

Geological foundations for smart cities: Comparing early Rome and Naples

Geological knowledge is essential for the sustainable development of a "smart city" -- one that harmonizes with the geology of its territory. Making a city "smarter" means improving the management of its infrastructure and resources to meet the present and future needs of its citizens and businesses. In the May issue of GSA Today, geologist Donatella de Rita and classical archaeologist Chrystina Häuber explain this idea further by using early Rome and Naples as comparative examples.

The authors describe Rome prior to Republican Times as a smart city because its expansion did not substantially alter the natural features of the area, and natural resources were managed to minimize environmental risks. Rome, which had at that time an economy based on agriculture, developed on small hilltops, and its position on the Tiber alluvial plain ensured fertile soils and easy commerce between river banks. Farms were plentiful, even inside the city walls, ensuring the self-sustenance of the city. Rome was also favored by an abundance of water resources, such as the Tiber and Aniene Rivers, and several natural springs inside the city walls.

In contrast, during the same period, Naples was exposed to more geological hazards and had fewer natural resources. Naples was located within an easily defendable bay, and as such its economy was dominated by sea trade. The rugged geomorphology of Naples' interior territory significantly limited agriculture and diversification. Rather than being able to expand outward, Naples mostly grew vertically, using as foundations the natural marine terraces bordering the coast. Geomorphology, therefore, played a key role in constraining the importance of Naples to the Roman Empire, according to de Rita and Häuber.

Over time, however, rapid urban expansion and concomitant population growth led to the overuse of resources and increased hazards for both cities, write de Rita and Häuber. As a result, the cities became unstable and fragile, with disasters resulting from several natural processes, such as flooding, volcanism, CO2 emissions, and earthquakes.
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Reference:

Science Daily. 2015. “Geological foundations for smart cities: Comparing early Rome and Naples”. Science Daily. Posted: April 30, 2015. Available online: http://www.sciencedaily.com/releases/2015/04/150430113602.htm

Tuesday, June 30, 2015

Lapita colonised Tonga within two generations

It only took a generation or two for the first settlers of Polynesia to spread from their original colonisation site in Tonga, a new study has found. The rapid spread could have been driven by resource depletion and sibling rivalry, says archaeologist Professor Marshall Weisler of the University of Queensland.

"We now have a precise chronology for the settlement of Tonga and the radiating out and occupying the islands of Tonga," says Weisler.

"Within one human generation or so the first settlers explored the rest of the archipelago and put down additional daughter communities."

In 2012, Weisler worked with Professor David Burley of Simon Fraser University to establish that the first humans to colonise the Pacific arrived at Nukuleka, on the Tongan island of Tongatapu, around 2838 years ago.

Their conclusions were based on uranium isotope dating of coral abraders used by the Lapita people to make fish hooks, ornaments and tools.

Now, in a paper published in PLOS ONE, Weisler and colleagues have got a picture of how long it took the Lapita to spread to other islands in Tonga, and how long daughter populations stayed in touch with the founder population.

The researchers dated 65 samples (including coral abraders, animal bones, shell tools and charcoal from ovens) from 20 Lapita sites across the Tongan archipelago.

They combined uranium- and radiocarbon-dating techniques in a so-called 'Bayesian model' to get the most precise chronology of early Polynesian movement.

The chronology was also aided by an analysis of pottery styles, which changed over time.

Rather than taking hundreds of years before occupying the rest of Tonga, the findings suggest it only took the early settlers 20 or 50 years, says Weisler.

"The process of settlement is far more rapid than we thought before," he says. "It's generational."

Weisler says archaeological evidence suggests that there was some depletion of resources at the original site, which could have been one reason why some people went in search of new homelands.

But, he says, sibling rivalry could possibly also have contributed to the split.

"In Polynesian societies, the first-born male inherits the good stuff. They become the head of their lineage in time, they inherit property," says Weisler.

"If you're second-born it's not good because you don't get any of these things. This creates a tension between siblings."

Weisler says another factor is the Lapita's long-standing tradition of seafaring. In other words, they may have dispersed just because they were adventurers.

In a separate study Weisler and colleagues have found evidence that daughter populations in other parts of Polynesia tended to stay in contact with their parent population for about 300 years before breaking off completely.

The findings are a result of analysing the chemical fingerprints of stone adzes, which were essential tools for early Polynesians.

Weisler and colleagues now plan to investigate reasons for the break off between daughter and parent communities.
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Reference:

Salleh, Anna. 2015. “Lapita colonised Tonga within two generations”. ABC Science. Posted: April 29, 2015. Available online: http://www.abc.net.au/science/articles/2015/04/29/4211318.htm