Posted on 01/12/2005 8:00:35 AM PST by PatrickHenry
Genes that control the size and complexity of the brain have undergone much more rapid evolution in humans than in non-human primates or other mammals, according to a new study by Howard Hughes Medical Institute researchers.
The accelerated evolution of these genes in the human lineage was apparently driven by strong selection. In the ancestors of humans, having bigger and more complex brains appears to have carried a particularly large advantage, much more so than for other mammals. These traits allowed individuals with “better brains” to leave behind more descendants. As a result, genetic mutations that produced bigger and more complex brains spread in the population very quickly. This led ultimately to a dramatic “speeding up” of evolution in genes controlling brain size and complexity.
“People in many fields, including evolutionary biology, anthropology and sociology, have long debated whether the evolution of the human brain was a special event,” said senior author Bruce Lahn of the Howard Hughes Medical Institute at the University of Chicago. “I believe that our study settles this question by showing that it was.”
Lahn and his colleagues reported their data in a research article published in the December 29, 2004, issue of the journal Cell.
The researchers focused their study on 214 brain-related genes, that is, genes involved in controlling brain development and function. They examined how the DNA sequences of these genes changed over evolutionary time in four species: humans, macaque monkeys, rats, and mice. Humans and macaques shared a common ancestor 20-25 million years ago, whereas rats and mice are separated by 16-23 million years of evolution. All four species shared a common ancestor about 80 million years ago.
Humans have extraordinarily large and complex brains, even when compared with macaques and other non-human primates. The human brain is several times larger than that of the macaque — even after correcting for body size — and “it is far more complicated in terms of structure,” said Lahn.
For each gene, Lahn and his colleagues counted the number of changes in the DNA sequence that altered the protein produced by the gene. They then obtained the rate of evolution for that gene by scaling the number of DNA changes to the amount of evolutionary time taken to make those changes.
By this measure, brain-related genes evolved much faster in humans and macaques than in mice and rats. In addition, the rate of evolution has been far greater in the lineage leading to humans than in the lineage leading to macaques.
This accelerated rate of evolution is consistent with the presence of selective forces in the human lineage that strongly favored larger and more complex brains. “The human lineage appears to have been subjected to very different selective regimes compared to most other lineages,” said Lahn. “Selection for greater intelligence and hence larger and more complex brains is far more intense during human evolution than during the evolution of other mammals.”
To further examine the role of selection in the evolution of brain-related genes, Lahn and his colleagues divided these genes into two groups. One group contained genes involved in the development of the brain during embryonic, fetal and infancy stages. The other group consisted of genes involved in “housekeeping” functions of the brain necessary for neural cells to live and function. If intensified selection indeed drove the dramatic changes in the size and organization of the brain, the developmental genes would be expected to change faster than the housekeeping genes during human evolution. Sure enough, Lahn's group found that the developmental genes showed much higher rates of change than the housekeeping genes.
In addition to uncovering the overall trend that brain-related genes — particularly those involved in brain development — evolved significantly faster in the human lineage, the study also uncovered two dozen “outlier” genes that might have made important contributions to the evolution of the human brain. These outlier genes were identified by virtue of the fact that their rate of change is especially accelerated in the human lineage, far more so than the other genes examined in the study. Strikingly, most of these outlier genes are involved in controlling either the overall size or the behavioral output of the brain — aspects of the brain that have changed the most during human evolution.
According to graduate student Eric Vallender, a coauthor of the article, it is entirely possible by chance that that two or three of these outlier genes might be involved in controlling brain size or behavior. “But we see a lot more than a couple — more like 17 out of the two dozen outliers,” he said. Thus, according to Lahn, genes controlling the overall size and behavioral output of the brain are perhaps places of the genome where nature has done the most amount of tinkering in the process of creating the powerful brain that humans possess today.
There is “no question” that Lahn's group has uncovered evidence of selection, said Ajit Varki of the University of California, San Diego. Furthermore, by choosing to look at specific genes, Lahn and his colleagues have demonstrated “that the candidate gene approach is alive and well,” said Varki. “They have found lots of interesting things.”
One of the study's major surprises is the relatively large number of genes that have contributed to human brain evolution. “For a long time, people have debated about the genetic underpinning of human brain evolution,” said Lahn. “Is it a few mutations in a few genes, a lot of mutations in a few genes, or a lot of mutations in a lot of genes? The answer appears to be a lot of mutations in a lot of genes. We've done a rough calculation that the evolution of the human brain probably involves hundreds if not thousands of mutations in perhaps hundreds or thousands of genes — and even that is a conservative estimate.”
It is nothing short of spectacular that so many mutations in so many genes were acquired during the mere 20-25 million years of time in the evolutionary lineage leading to humans, according to Lahn. This means that selection has worked “extra-hard” during human evolution to create the powerful brain that exists in humans.
Varki points out that several major events in recent human evolution may reflect the action of strong selective forces, including the appearance of the genus Homo about 2 million years ago, a major expansion of the brain beginning about a half million years ago, and the appearance of anatomically modern humans about 150,000 years ago. "It's clear that human evolution did not occur in one fell swoop," he said, "which makes sense, given that the brain is such a complex organ."
Lahn further speculated that the strong selection for better brains may still be ongoing in the present-day human populations. Why the human lineage experienced such intensified selection for better brains but not other species is an open question. Lahn believes that answers to this important question will come not just from the biological sciences but from the social sciences as well. It is perhaps the complex social structures and cultural behaviors unique in human ancestors that fueled the rapid evolution of the brain.
“This paper is going to open up lots of discussion,” Lahn said. “We have to start thinking about how social structures and cultural behaviors in the lineage leading to humans differed from that in other lineages, and how such differences have powered human evolution in a unique manner. To me, that is the most exciting part of this paper.”
Variation is observed. Evolution is not. It is a leap of faith to say that because variation happens, evolution happens. You may as well say that because Chevys have different models, they must have trains and planes too.
We are the most intelligent species on the planet, but we're not the only intelligent species on the planet.
Furthermore, there are plenty of ancestors/relatives of homo sapiens that were quite intelligent, even by human standards. Neanderthals, for example.
Actually, I'm not trying to prove that the Theory of Evolution is true. All I'm saying is that as a theory it's got a lot going for it, and it hasn't been disproven, even after 150 years. Nothing else explains the phenomenon of speciation, unless you just want to say "God did it", but that's a theological argument, not a scientific one. That's part of the problem in this debate. We're talking apples and oranges.
Evolution explains why 'God' gave men nipples.. ;)
Your assuming this all took place in Pleasantville.
Still happening now. Look at how dim-witted lefties have stopped reproducing.
explain why they are not a credible source of science. explain how the pope is soooooooo all knowing.
Fine, if you want me to explain evolution, it simply put was some accident that created the universe, and some accident that happened on earth to create a little bit of life, such as bacteria. It was from that that we evolved using natural selection. I HAD to learn what evolution is in the BJU science books, IN THIRD GRADE. but it was tought as a theory, not fact. you guys have no proof that evolution exists, I have yet to see it, all you have is "evidence" from "millions" of years ago.
Well, first of all, I am a woman. And all you have to do is watch Jerry Springer to see the men fathering multiple children - lol.
True—now. But shift back hundreds of thousands of years and the situation changes drastically. In a world where human numbers were small and the war for existence was on-going and brutal, smarter individuals clearly had an advantage and no doubt succeeded in reproducing more often than dumber ones. Nowadays, we're so numerous and so successful as a species that intelligence gets downgraded a bit as far as fitness to reproduce is concerned. Still, when you were in high-school, would you have been attracted to a Beavis & Butthead-type guy or to a McGyver-type guy?
LMAO
yup -ever adapting dogma is getting pretty deep in evolutionism churches... Next we will have the evolutionary big bang and or big spurts connected via missing links...
Observations are able to show the frequency of phenomena according to the times, places, populations or circumstances studied. In this way facts are discovered, but facts do not constitute a criterion for judging the truth of a complete theory lacking incomplete facts. The observation of the phenomena is certainly to be linked with truth; however, the linkage itself true does not by default impart truth into theory incorporating such...
Every person's brain will someday be just another decaying blob of matter.
Evolution explains why 'God' gave men nipples.. ;)
And why marsupial fossils can be found in Antarctica...
And why the sensors on our retinae face the wrong way (badly designed but still work)...
and... (repeat for thousands of curiosities of that evolution explains)
"This accelerated rate of evolution is consistent with the presence of selective forces in the human lineage that strongly favored larger and more complex brains. "
Beaurocracies. Nahhh!! that would have a retrograde impact. Human intelligence evolved DESPITE governments, not because of them.
I'm not sure that's quite true. IIRC, goldfish have been bred from coi over the last 1500 years or so and are now a completely species.
Okay, I'll bite: How is it that a "group" gets the wing gene? I don't recall any suggestion in the theory that there exists a mass coincidental genetic deviation. This is the crux of the "complex" theory. If evolution is to be considered the way it is taught today you must believe the changes take place on a individual basis and so slowly that it is (nearly) imperceptible. It makes sense in the development of a giraffe's neck or the development of the human hand. System integration (the complexity of the human eye) is quite different.
McGyver, of course!
"..it was tought as a theory, not fact. you guys have no proof that evolution exists"
Religion boils down to a question of faith as well. In terms of proof, science has more going for it.
Why do you correlate smartness with feebleness?
"It is perhaps the complex social structures and cultural behaviors unique in human ancestors that fueled the rapid evolution of the brain"
I believe it has more to do with the physical environment. For example, in an ice-age environment, selection pressure is at its strongest. Only the most intelligent and those who are able to cooperate with one another will survive and reproduce. It isn't a matter of smart people having more kids; it is a matter of stupid people dying off.
Culture or social interaction may explain verbal intelligence, but it does not explain logic, mathematics, abstraction, and visual-spatial abilities.
The wing example was used to make the point that some genes take a lot longer to saturate a gene pool than others, I should have taken a little longer to come up with a better example of the point.
McGyver, of course!
I rest my case!
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