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Why pygmies are so short?
For years, scientists have been wondering why Pygmies of West Africa have such short stature. Men grow to a maximum of five feet tall and women about a half foot shorter, while in neighboring groups, such as the Bantus, the average height are 5 feet.In order to see whether these differences were genetic or an adaptation to living in a tropical environment, researcher analyzed their genomes.
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Pygmies and Bantus in West Africa have mixed for thousands of years but were separated genetically about 60,000 to 70,000 years ago; then 4,000 to 5,000 years ago, they started inbreeding.
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Mating between some Pygmy women with Bantu men had as a result half-Bantu babies. This phenomenon integrated Bantu genes into pygmy population. These women and their offspring stayed in the Pygmy population, so there was no mix with the Bantu. Nonetheless, offspring resulting from mating between Pygmy men and Bantuwomen aren’t common, so the Bantus don’t have many Pygmy genes.
Researchers first investigated which regions of the Pygmies’ genomes reflected Pygmy or Bantu ancestry. The conclusion was that the more Bantu ancestry someone had, the taller he or she was, which supported the idea that Pygmy stature has genetic roots.
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This study, leaded by Sarah Tishkoff, analyzed the SNPs of 70 Pygmies and 60 Bantus trying to find those that may have been naturally selected as they gave pygmies an advantage in surviving and passing on their genes.
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Some of these selected SNPs occurred in a region of chromosome 3 that differed between Bantus and Pygmies, and were linked to height. They also found new changes in hormone pathways and immunity that seemed to have a relation with the short stature of the pygmies. One of the SNPS, called CISH, has been shown to interact with growth hormone receptor by inhibiting the signal; it’s also known that this gene confers immunity against Malaria.
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The immunity component could be a result of natural selection, as it helps the pygmies fight off infections, which are prevalent in their habitat. The short height could just be a byproduct of these changes.
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Original divulgative article: http://www.nature.com/news/hunt-for-genetic-link-to-pygmy-height-yields-clue-1.10517
The complete study: http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1002641
Cooperation not competition: Chimps can be team players
Our species is thought to be unique in its ability to achieve cooperation, whilst the chimpanzee, our closest relative, is usually described as competitive. However, a new study revealed that, given the choice between cooperation and competition, chimpanzees opted for the first option five times more frequently.
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This research carried by the Yerkes National Primate Research Center, suggests that chimpanzees, considered to be aggressive and competitive, actually prefer cooperating over competing. The work shows that chimps work together at similar rates as humans, and when violence does occur, it is usually caused by an ape who is not being a team player.
To reach this conclusion, researchers worked with 11 chimps in an environment that simulates their usual conditions and devised an experiment to evaluate cooperation, defined as two or more chimps working together to achieve a food reward. Apes had nearly 100 hours to obtain their prize with other chimps as onlookers, so there were lots of chances for competition to occur. The researchers defined “competition” as episodes of violence or prize stealing.
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In 94 hour-long test sessions, the chimps cooperated with one another 3,565 times five times more often than they were in competition. On top of this, apes used plenty of strategies to punish competitive behaviors or to prevent freeloading.
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“It has become a popular claim that human cooperation is unique,” study co-author Frans de Waal, a primatologist at Yerkes, said in a statement. “Our study is the first to show that our closest relatives know very well how to discourage competition and freeloading.”
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Plenty of other species exhibit cooperative behavior, for example the ants. But as lead author MaliniSuchak explains, what her team observed in chimps is even more impressive. “Although cooperation is widespread across species, cooperation in ants, for example, as well as in many other species is directed toward kin and is basically preprogrammed,” she says. “Our study shows that chimpanzees are really thinking about cooperation and actively making decisions that maximize cooperation and minimize competition.” She adds: “Cognitively, what they did in our experiment is much closer to what humans do when we cooperate than it is to what ants do when they cooperate.”
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As Suchaksays, her new findings signify that the origins of our cooperative behaviors may go farther back than it was thought. “In the past, chimpanzees have been characterized as overly aggressive and competitive, which resulted in people suggesting human cooperative behavior evolved relatively recently and is somehow distinct from cooperation observed in other species,” she says. “Our findings are a reminder that humans are animals, after all.”
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Divulgative article (in Spanish) http://elpais.com/elpais/2016/08/22/ciencia/1471883542_652369.html
Original article: http://www.pnas.org/content/113/36/10215
The duplication of the SRGAP2 made us more human
For years, researchers have been looking for differences between the genome of humans and other primates to explain what distinguish us from our closest primate kin. Until the moment, the main way to make those comparisons consisted onsearching changes of the sequence of nucleotides.
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However, studies published in Cell, suggest DNA duplication errors that occurred millions of years ago might be important in the evolution of the complexity of the human brain. These duplications may have allowed our brain to make more neural connections at greater distances, shaping our brains into what they are now.
In 2010, a group led by Evan Eichler,identified 23 genes that have only been duplicated in humans, and no other apes. Among these, SRGAP2 stood out.
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Years later, two groups led by Evan Eichler and Franck Polleux found that humanshave three copies of the SRGAP2 gene. The second of these copies, SRGAP2C, is particularly interesting because it affects the development of neurons, and produces characteristicsthat are distinctively human.
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The authors found that the original gene was first duplicated around 3.4 million years ago to create SRGAP2B. This copy was itself duplicated 2.4 million years ago to create SRGAP2C, and again 1 million years ago to produce SRGAP2D.These copies have evolved in different ways. Whilst B and D versions have probably mutated to the point that they are genetic junk, the C-copy is very different.
The SRGAP2C protein blocks the action of the protein coded by the ancestral gene. According to the team, the inhibition if the SRGAP2A (ancestral) protein, allows neurons to acquire a new function: neurons would produce denser called dendritic spines.
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“If you’re increasing the total number of connections, you’re probably increasing the ability of this network to handle information,” Polleux says. "It’s like increasing the number of processors in a computer."
There is still a lot to discover, SRGAP2 is just one of more than 30 genes that have been duplicated specifically in humans. The teams are now busy trying to analyze these genes and understand their evolution.
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James Sikela, and evolutionary geneticist at the University of Colorado, and his team have identified some duplicated genes that are unique in humans. “Finding the genes that make us human may be challenging,” he says, “but the resources we now have to ask such questions are unprecedented.”
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Divulgation article: http://www.nature.com/news/human-brain-shaped-by-duplicate-genes-1.10584?WT.ec_id=NEWS-20120508
Original article: https://www.sciencedaily.com/releases/2012/05/120503125804.htmhttps://www.sciencedaily.com/releases/2012/05/120503125804.htm
There is evidence of malaria's existence 2,000 years ago
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An analysis of 2,000-year-old human remains from several regions across the Italian peninsula has confirmed the presence of malaria during the Roman Empire, addressing a longstanding debate about its pervasiveness in this ancient civilization.
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The answer is in mitochondrial genomic evidence of malaria, coaxed from the teeth of bodies buried in three Italian cemeteries, dating back to the Imperial period of the 1st to 3rd centuries Common Era.
The genomic data is important, say researchers, because it serves as a key reference point for when and where the parasite existed in humans, and provides more information about the evolution of human disease.
"Malaria was likely a significant historical pathogen that caused widespread death in ancient Rome," says evolutionary geneticist Hendrik Poinar, director of McMaster's Ancient DNA Centre where the work was conducted.
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A serious and sometimes fatal infectious disease that is spread by infected mosquitoes, malaria and its parasite Plasmodium falciparum, is responsible for nearly 450,000 deaths every year, the majority of them children under the age of five.
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"There is extensive written evidence describing fevers that sound like malaria in ancient Greece and Rome, but the specific malaria species responsible is unknown," says Stephanie Marciniak, a former post doctoral student in the Ancient DNA Centre and now a postdoctoral scholar at Pennsylvania State University.
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"Our data confirm that the species was likely Plasmodium falciparum, and that it affected people in different ecological and cultural environments. These results open up new questions to explore, particularly how widespread this parasite was, and what burden it placed upon communities in Imperial Roman Italy," she says.
Marciniak sampled teeth taken from 58 adults and 10 children interred at three Imperial period Italian cemeteries: Isola Sacra, Velia and Vagnari. Located on the coast, Velia and Isola Sacra were known as important port cities and trading centres. Vagnari is located further inland and believed to be the burial site of labourers who would have worked on a Roman rural estate.
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Using techniques developed at McMaster and abroad, researchers mined tiny DNA fragments from dental pulp taken from the teeth. They were able to extract, purify and enrich specifically for the Plasmodium species known to infect humans.
It was a difficult and painstaking process, complicated by the very nature of the disease.
Usable DNA is challenging to extract because the parasites primarily dwell within the bloodstream and organs, including the spleen and liver, which decompose and break down over time -- in this instance, over the course of two millennia.
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Marciniak, Poinar, and Tracy Prowse from McMaster, alongside Luca Bandioli from the Luigi Pigorini National Museum of Prehistory and Ethnography in Rome and Edward Holmes from the University of Sydney recovered more than half of the P. falciparum mitochondrial genome from two individuals from Velia and Vagnari.
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P. falciparum remains the most prevalent malaria parasite in sub-Saharan Africa and the most-deadly anywhere, responsible for the largest number of malaria-related deaths globally.
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Original article: http://www.cell.com/current-biology/abstract/S0960-9822(16)31201-5
Lucy spent so much time in trees
Lucy, the first complete skeleton of the erliest hominid ever found, is suggested to have been a very good climber. Her fossil, which is 3,18 million-years-old, is what give the researchers the clue about this fact.
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“Most people have agreed for a while that she did some tree climbing, or had done tree climbing in the recent past, but there were a lot of questions about whether it was a major part of her lifestyle,” said Christopher Ruff, a professor of functional anatomy and evolution at Johns Hopkins University School of Medicine and the lead author on the study. “We’re saying she probably used trees on a daily basis.”
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The authors turned to a micro-CT scan of Lucy’s skeleton to come to this conclusion. Lucy’s fossilized bones had been scanned not long after their discovery in the early 1970s, but the instruments back then were not powerful enough to show the internal structure of her bones.
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Being able to peer into the interior of Lucy’s bones has shed a whole new light on how Lucy lived her life, Ruff said.
Ruff and his team concentrated on cross-sectional scans of Lucy’s one remaining thigh bone and her two remaining upper arm bones. In particular, they were looking for how tissue was distributed along the bone shaft as an indication of strength.
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Next, the group compared the relative strength of Lucy’s bones to those from a database of more than 1,000 pre-20th century humans and 100 chimpanzees.
Previous work on chimpanzees and gorillas revealed that measurements like these matched up with locomotion behavior.
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For example, animals that climbed trees had relatively stronger upper limbs compared with those that did not climb trees.
The authors found that Lucy’s upper limb strength was intermediate between humans and chimps, but a bit closer to the chimp side. This suggests that she used her upper limbs significantly more than we do, although not as much as chimpanzees, which frequently climb trees.
He added that it is hard to imagine what other factors besides tree climbing would have created the bone tissue distribution he observed in Lucy’s upper arm bones.
“There is really no other explanation for that kind of overloading,” Ruff said.
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Original article: http://journals.plos.org/plosone/article?id=info%3Adoi/10.1371/journal.pone.0166095