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Hermit
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Evolution in the Fast Lane
« on: 2006-08-17 18:02:26 » |
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Fastest-evolving human gene linked to brain boost
Source: Nature via New Scientist
Authors: Not Credited
Dated: 2006-08-16
The fastest evolving gene in the human genome is one linked to brain development, researchers say.
A study of differences between the human and chimp genomes has identified a gene associated with neural growth in the cerebral cortex – the part of the brain involved in processing thoughts and learning – as having undergone “accelerated evolutionary change”.
Katherine Pollard and colleagues at the University of California Santa Cruz, US, suggest that the fast-changing gene may help explain the dramatic expansion of this part of the brain during the evolution of humans.
They identified the rapidly evolving region of DNA – called human accelerated region 1 (HAR1) – after carrying out an extensive computational comparison between the genomes of humans, chimpanzees and other vertebrates.
Critical role
There are only two changes in the 118 letters of DNA code that make up HAR1 between the genomes of chimps and chickens. But chimps and humans are 18 letter-changes apart. And those mutations occurred in just five million years, as we evolved from our shared ancestor.
“That is an incredible amount of change to have happened in a few million years,” Pollard notes.
Subsequent experiments looking at the brains of human and primate embryos revealed that HAR1 is part of two overlapping genes. One of these genes, called HAR1F is active in nerve cells that appear early in embryonic development and play a critical role in the formation of the layered structure of the human cerebral cortex.
The role of the other gene, called HAR1R, is less clear, but it also appears also to be involved in cortex development.
"Very suggestive"
The researchers point out that these genes do not appear to code for any proteins, but are what is known as an RNA genes.
“We don’t know exactly what it does, but the evidence is very suggestive that HAR1F is important in the development of the cerebral cortex, and that’s exciting because the human cortex is three times as large as it was in our predecessors,” says David Haussler, director of the Center for Biomolecular Science and Engineering at the University of California Santa Cruz, who assisted with the study.
“Something caused our brains to evolve to be much larger and have more functions than the brains of other mammals,” he points out.
Journal reference: Nature (DOI: 10.1038/nature05113)
Scientists find brain 'gene'
MAY PLAY ROLE IN HUMAN INTELLECT
Source: Nature via Mercury News
Authors: Lisa M. Krieger
Dated: 2006-08-17
Researchers at UC-Santa Cruz say they have found a gene that may provide operating instructions for the human intellect.
There is no single gene for intelligence because an enormous number of genes are involved in building a brain, said geneticist David Haussler, who led the research, published in today's issue of the journal Nature.
But the gene, called HAR1, is believed to be important because it has undergone evolutionary changes that are unique to humans -- and is active during a critical time in complex brain development, Haussler said. He hopes that future work will solidify the link.
Haussler believes the gene may play a role in construction of the cerebral cortex -- that thick and folded mass of cells on the surface of the human brain that gives us the unique ability to play chess, write violin sonatas and build explosives.
One of the longstanding mysteries of science is how humans -- alone in the animal kingdom -- are able to master intellectually complex activities.
"Why are we smarter than apes? What happened? That was the motivation behind our research," Haussler said.
Scientists know that about 2 million years ago, the human brain began to enlarge until it became about three times larger than that of chimpanzees, our closest evolutionary cousin. In addition, they believe there were changes in cellular structures that created cognitive improvement.
Haussler and his team reasoned that these rapid changes must have left their impression on the human genome.
"It's got to be something that happened in our genome -- a genetic change,'" he said.
In its research, the University of California-Santa Cruz team first identified the parts of the human genome that have changed most dramatically since we parted ways with chimps 5 million to 7 million years ago.
They found that the HAR1 region is essentially the same in all mammals except humans -- and that sometime after humans diverged from chimps, it changed in 18 different places. It changed because of mutations that proved advantageous to early humans, Haussler said.
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With or without religion, you would have good people doing good things and evil people doing evil things. But for good people to do evil things, that takes religion. - Steven Weinberg, 1999
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Hermit
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Re:Evolution in the Fast Lane
« Reply #1 on: 2006-08-17 22:06:54 » |
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How we differ from our cousin, the chimp
Scientists think a part of our DNA linked to speech and thought took a huge leap forward
[Hermit: More notes on this announcement, differentiated primarily from those previously introduced here by what may be yet another silly American attempt to present a "balanced perspective" to the indefensible. If not that, then attempting to introduce an "Intelligent Design" based challenge in a deniable form. It is remarkably difficult to differentiate between these possibilities, particularly given the location and the non sequitor post scriptal nature of the ID related comments. Perhaps the Chronicle is trying very hard not to offend its idiotic "life loving" audience down in Crawford* which is nauseated by any suggestion that they share simian DNA.
In this piece, I did find the allusion to speech development centers at 200kybp interesting; particularly given that the consensus is that we didn't have the mechanisms for speech until 70-130kybp and didn't have the brain potential until 110-140kybp. Based on that, I suspect that either the dating will be revised, or that we will eventually find that FOXP2 was linked to some other development (e.g. tool making) and either transformed or was co-opted into the speech process.
*Whose life loving nature is presumably attested to by the fact that they would seemingly prefer to see blastocysts being flushed to the sound of bombs over Baghdad and Beirut, rather than they be used for research. Can you say that again please?]
Source: The Houston Chronicle
Authors: Eric Berger
Dated: 2006-08-17
Scientists believe they may have found a narrow slice of DNA that separates us from chimpanzees.
Current research holds that humans and chimps split on the evolutionary tree about 7 million years ago. In identifying a section of DNA that has changed more than 70 times as rapidly as the rest of the human genome, researchers may have found out how, though not why, that split came about.
"The suggestion is that this region of DNA is crucial to the development of uniquely human brains," said David Haussler, a molecular biologist at the University of California at Santa Cruz and the co-author of a study reported in the journal Nature.
Finding the gene, or genes, that underpin the runaway brain of humans as compared to every other species is one of modern biology's holy grails.
"It's not like the problem is solved," said Richard Gibbs, director of Baylor College of Medicine's Human Genome Sequencing Center. "But this is a nice paper. And it's persuasive to me that they have found a significant difference in the genomes.
"But it's unknown how many significant differences will have to add up to make us different from chimpanzees."
Humans and chimps share about 98.5 percent of the same DNA.
As part of the human reproductive process, male and female DNA are mixed, with the offspring inheriting genes from both. Sometimes, as part of this process, a DNA letter here and there is changed, or mutated.
Such mutations often have negative consequences and, as part of a so-called "negative selection," are eventually weeded out of the gene pool. Some gene mutations with negative consequences survive, of course, such as the gene responsible for cystic fibrosis. But most are washed out.
50 regions identified
In searching for what makes humans human, Haussler's team decided its best bet was to identify regions of the genome — the blueprint of life for an organism — that have evolved most rapidly since chimpanzees and humans diverged.
Of the nearly 50 regions they identified, one that had changed a lot stood out.
More intriguingly, that particular section of DNA lies on a gene that plays a role in developing the region of the brain identified with higher-level thinking and speech.
The study is one of the first to harness the ability to mine the trove of data accrued as part of the Human Genome Project and later efforts. Since a draft of the human genome was completed five years ago, geneticists have raced to complete the sequences of other animals.
For the new study, Haussler's team compared the 3 billion-DNA letter genome of humans with that of the chimp, mouse and rat.
Searching across the four genomes, the team looked for regions of DNA about 100 letters long that had made the biggest leaps. One, they found, had changed nearly twice as much as any other region, with 18 letters of DNA different between humans and chimps. A similar stretch of chicken DNA, they found, has all but two letters in common with the chimp DNA.
"That shows that this region of the DNA had been stable for a long time, hundreds of millions of years," Haussler said.
The next question was to determine the function of this particular region of DNA, which was found on a gene named "HAR1." The gene produces an RNA molecule that aids in the formation of the brain's neocortex between the seventh and 19th weeks of an embryo's development into a fetus.
This part of the brain is thought to be critical to higher levels of thinking, including the development of speech.
Largely because of this accelerated development of the cerebral cortex, the human brain has grown three times larger than that of the chimpanzee in just 7 million years.
It's tempting, therefore, to suggest that the tiny portion of the human genome that has evolved most rapidly since then may represent the spark that led to modern human beings.
Genes and speech
Still, some scientists say it must have taken more than a handful of these kingpin genes to trigger the development of humans. A few years ago, scientists identified a gene named FOXP2, which appears to have rapidly evolved in humans about 200,000 years ago and is important for human speech.
"It's hard for me to imagine that two or three major genetic changes would produce the differences we see between humans and chimpanzee," said Jeff Rogers, a geneticist at the Southwest National Primate Research Center in San Antonio.
Like the other scientists, Rogers was impressed by the scale of the evolution of the HAR1 gene when the odds were so seemingly stacked against it.
"A change like what they found?" Rogers said. "It's way, way out there on the probability curve."
The surprising find is unlikely to sway those who dispute the idea that humans and apes share a common ancestor. Surveys regularly show 40 percent of Americans don't accept the theory of evolution.
"The authors note that the evolutionary changes in question happened rapidly, and they can, apparently, document some of the necessary changes," said mathematician and philosopher William Dembski, a former faculty member at Baylor University and an advocate for intelligent design.
"But that hardly explains what caused the changes and how they were coordinated to bring about our more complex and developed brains."
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With or without religion, you would have good people doing good things and evil people doing evil things. But for good people to do evil things, that takes religion. - Steven Weinberg, 1999
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