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.”
Yep.
"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.”
If we're believing that God directed the evolution of the human brain, at what point was that human brain the Adam of the Bible?
That's not true. Look up the example of the Peppered Moth in Britain that changed color when their tree trunks where stained black by coal soot during the Industrial Revolution. Before that, most of them where white, but there where a few black ones (variation in species). In a short time, the white ones mostly disappeared and the black ones predominated. That's a perfect example of selective pressure causing a species to change. True, they did not become a new species, but the example shows how species change due to environmental pressure.
Also, the fossil record shows many examples of evolution. Species appear and disappear in the fossil record throughout time. The Creation story doesn't explain that.
Yup, evolution even explains why whales and snakes have leg bone remnants..
The theory of evolution has nothing to do with where life came from or how the universe began.
It was from that that we evolved using natural selection.
This statement is basically true.
I HAD to learn what evolution is in the BJU science books, IN THIRD GRADE. but it was tought as a theory, not fact.
What's your point? Nobody is claiming that the TOE is anything more than a theory.
you guys have no proof that evolution exists, I have yet to see it, all you have is "evidence" from "millions" of years ago.
What kind of proof would be adequate for you to accept that evolution occurs?
"...in general high intelligence is not a particularly useful adaption. Sure we are numerous and dominate our planet for the last few-thousand years. The Sauropods managed that for 100 million years."
Extremely bad comparison. Humans are unique in that we lack almost any physical adaptations to the environment. Sauropods had every physical adaption needed to survive as long as they did. The only thing we have is intelligence. Not only is it a useful adaptation, it is our ONLY adaptation.
Well, I have to agree with Jay777.
Nobody has been able to deliver a successful argument to suggest that Creationism could not have been responsible for evolutionism. If God is within all of us, he also has the ability to tweak us for His purposes.
Personally, I do not believe that evolution just happened, but I can phathom the possibility, or probability that God controls evolution.
If we have proof of some evolution, we have proof of evolution. What we do not have is proof of how life began and here is where Creationism and the Bible chimes in.
If you do not believe at all in evolution, please explain to me why all human bones discovered are not Homo Sapiens.
I didn't know that. If it's true then it's certainly a point in favor of my Evolutionist argument. However, if they can still breed with the ancestral Coi then they are still the same species, as dogs and wolves are. They haven't diverged enough to be considered different species.
I expressed myself badly. I was merely trying to downgrade the idea that humans, with their intelligence, represent some kind of pinnacle of evolution that can regard itself as far more successful than past species.
Sorry, my fault. I understand what you mean now, which is right.
The chances of teddy turning republican are as remote as the chances of liberals ever regaining political power again -liberals are at a political and genetic dead end...
Try the following link for some info that may interest you:
I would strongly dispute that notion. Pure, unadorned evolution has one, singular measure of success: the ability to survive long enough to propagate. There is only one species with the capability to ensure that it survives the total annihilation of the planet itself. Guess which one that is?
I am unsure, but probably the point at which H. Sapiens diverged from its immediate predecessor.
I don't know. Even Einstein got around. Evolution doesn't distinguish between legitimat and illegitimate.
I'm not takling PhDs here. I'm talking about the guys that make the most money and have the most power.
But if the pressure was more, then selection wouldn't "work any harder," it would work the same as it does elsewhere. They've flipped it, adding something beyond the "normal" result of pressure.
Also, the "Special Event" quote. I take this to mean unlike all other events. Again, not conforming to the other natural selection events.
They are saying that the development, selection for, greater brain size/power was favored among the human as opposed to the other primate species. This doesn't compute scientifically and I think that's why we see this type of "explanation."
That's not even close to being true. You should crack a biology book sometime.
I think we need to observe the introduction of a new genus through variation of an existing species. It seems if variation could "leap" into a new genus classification the evolution theory would have a few more allies.
Viruses?
DU is descended from the control group.
I would think the smart women would want to choose smart men.
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