Human Brain Evolution Was a 'Special Event'

Howard Hughes Medical Institute ^ | 29 December 2004 | Staff

[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.”

[Dataman]

Because one formation of layered sediments formed in a day, that does not therefore mean that all layered sedimentary formations were formed in a short timeframe.

Of course that is not a claim I made.

[GreenFreeper]

ping

[Dataman]

Okay, let's put it this way: You have been hit over the head with literally mountains of evidence.

And the above illustration is typical of your "evidence." But remember Lewontin said it's not the evidence, but the commitment to materialism.

[Dataman]

However, you then take that one square-peg truth and try to pound it in every stratigraphic round hole that you come across.

The fact that layers can and did form rapidly seems to make materialist very uncomfortable.

[Dataman]

The fact that layers can and did form rapidly seems to make materialists very uncomfortable.

[WildHorseCrash]

We take the side of science in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, and in spite of the tolerance of the scientific community for unsubstantiated just-so-stories, because we have a prior commitment, a commitment to materialism. It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counterintuitive, no matter how mystifying to the uninitiated. Moreover, that materialism is an absolute, for we cannot allow a Divine Foot in the door." - Richard Lewontin

You're not pulling this out-of-context quote again, are you??? Sigh.

This is from a review of Carl Sagan's book The Demon-Haunted World. When you look at this quote in context, he is really making the point that one of the difficulty science has in educating people is the fact that some things which are true seem to lack "common sense" to those who don't know science. Nonetheless, they are true. Thus, Lewontin is really saying, is, essentially, that people have difficulty believing in science because they are ignorant of how science works. What he is saying is that the fact that science is "counterintuitive... [and] mystifying to the uninitiated" simply means they don't understand it, and scientists have to do a better job in teaching it.

From the article:

With great perception, Sagan sees that there is an impediment to the popular credibility of scientific claims about the world, an impediment that is almost invisible to most scientists. Many of the most fundamental claims of science are against common sense and seem absurd on their face. Do physicists really expect me to accept without serious qualms that the pungent cheese that I had for lunch is really made up of tiny, tasteless, odorless, colorless packets of energy with nothing but empty space between them? Astronomers tell us without apparent embarrassment that they can see stellar events that occurred millions of years ago, whereas we all know that we see things as they happen. When, at the time of the moon landing, a woman in rural Texas was interviewed about the event, she very sensibly refused to believe that the television pictures she had seen had come all the way from the moon, on the grounds that with her antenna she couldn't even get Dallas. What seems absurd depends on one's prejudice. ...

Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural. We take the side of science in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community for unsubstantiated just-so stories, because we have a prior commitment, a commitment to materialism....

I see this all the time on these boards, when people say, "I don't believe in evolution because it just doesn't make any sense to me..." That something appears to go against common sense is no proof that it is not true.

[Dataman]

Oh, and FWIW, I have my own doubts about some of the dynamics of Darwinian evolution.

I have no problem with the benign evolutionists; I was one myself. And I don't lump them in with the malignant evolutionists who favor ridicule over reason.

[Dimensio]

I'm sorry but there is no way I can belive evolution, there is just no way it is possible. The chances to create life as complicated as Human beings is just far too remote

This is called "argument from incredulity".

[Dimensio]

Blank-Slate Syndrome -- a horrible way to go through life.

I think at this point it's safe to say that he's just a liar.

[Dataman]

Yes, we all know that Lewinton didn't mean what he said. He really didn't mean his commitment to materialism didn't bias him at all.

And Antony Flew really didn't abandon atheism.

And Darwin really didn't mean half of what he wrote.

The quotation is fairly lengthy. It wasn't a sound bite. It wasn't even a sentence. It was an entire paragraph that obviously embarrassed Sagan. So if these men are so brilliant, why can't they say what they mean?

[dirtboy]

The fact that layers can and did form rapidly seems to make materialist very uncomfortable.

No, it doesn't. It simply fails to buttress your position in any manner.

[VOYAGER]

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.

I sure hope God reads this thread so He can know what a good job He was doing when He didn't know what He was doing before He got through doing what He had no idea what a terrific job He was doing!

Thank you God!

[dirtboy]

Of course that is not a claim I made.

Not correct - you clearly inferred just that in post #141 (bolded sections are your responses):

As for the flood, it supposedly lasted 40 days and nights,

Closer to a year.

That takes millions of years. Are you telling me that all those deposits formed in forty days?

How long do you think these layers took to form?

[Junior]

A fixation on wings and chickens... Ted, is that you?

[_Jim]

Mmm, Sovek, would you care to state what the theory of evolution says?

After he's done exposing his ignorance about which he says he 'doesn't believe', send him here for some edification:

The Origin of Species
Charles Darwin

Gotta love the 'net, where even the torch-wielding pitchfork-thrusting Neanderthals can be shown the 'source documents' in an argument ...

BONUS - here's the opening paragraph from the preface.

I WILL here give a brief sketch of the progress of opinion on the Origin of Species.

Until recently the great majority of naturalists believed that species were immutable productions, and had been separately created. This view has been ably maintained by many authors. Some few naturalists, on the other hand, have believed that species undergo modification, and that the existing forms of life are the descendants by true generation of pre-existing forms. Passing over allusions to the subject in the classical writers,* the first author who in modern times has treated it in a scientific spirit was Buffon.

But as his opinions fluctuated greatly at different periods, and as he does not enter on the causes * Aristotle, in his 'Physicae Auscultationes' (lib. 2, cap. 8, s. 2), after remarking that rain does not fall in order to make the corn grow, any more than it falls to spoil the farmer's corn when threshed out of doors, applies the same argument to organization: and adds (as translated by Mr Clair Grece, who first pointed out the passage to me), 'So what hinders the different parts [of the body] from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident.

And in like manner as to the other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity, and whatsoever things were not thus constituted, perished, and still perish. or means of the transformation of species, I need not here enter on details.

[_Jim]

Evolution is rejected because it is bad science, bad logic and not even very good story telling.

Sheer, unalloyed idiocy (IOW, "idiocy in it's purest form").

[WildHorseCrash]

Yes, we all know that Lewinton didn't mean what he said. He really didn't mean his commitment to materialism didn't bias him at all.

No, it means that you didn't understand what he wrote. He said that the commitment to materialism is the only thing that keeps scientist doing science, and not conjuring up stories based on wishes or pretending four-thousand year-old mid-Eastern creation stories are factual history.

And Antony Flew really didn't abandon atheism.

An 81 year-old philosopher now believing in some kind of deity...Wow, there's a shocker. Interesting description of God, by Mr. Flew, by the way: "I'm thinking of a God very different from the God of the Christian and far and away from the God of Islam, because both are depicted as omnipotent Oriental despots, cosmic Saddam Husseins,"

And Darwin really didn't mean half of what he wrote.

This doesn't even make any sense. Of course he meant what he wrote.

The quotation is fairly lengthy. It wasn't a sound bite. It wasn't even a sentence. It was an entire paragraph that obviously embarrassed Sagan. So if these men are so brilliant, why can't they say what they mean?

Again, just because you can't understand him does not mean he isn't saying what he meant.

Further, just because your quote was long does not mean that it could not be out of context. You even cut out the topic sentence of his paragraph: "Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural." In other words, scientists have a commitment to materialism because it is the only thing separating scientific belief from the superstitious nonsense the yokels believe in.

As for Sagan, he believed that if you teach ignorant people the truth, they will rise out of their ignorance. Lewontin believes that they will not, because he views science as a bit less grand than Sagan, but believes that if you show people how science is done, they will accept it and rise out of their ignorance. Seeing discussions of ID on FR tells me that those who believe in ID and creationism are happy to wallow in their ignorance, and won't rise up even if you gave them a rope.

[Dataman]

C'mon DB, I give you more credit than that. Am I wrong for expecting you to abstain from fabrication like so many of your brethren? Show me where I claimed all layers are laid down quickly through water action.

Is the frequent fabrication of material the standard evolutionary alternative to conceding a point?

[Dataman]

No, it means that you didn't understand what he wrote.

That's just another dusty tactic from the evos worn out bag of tricks. You're smart and anyone who disagrees with you is stupid. I guess that puts you in the category of malignant evolutionist.

An 81 year-old philosopher now believing in some kind of deity...Wow, there's a shocker.

Like Gene Edward Veith said, it would be like Billy Graham renouncing Christianity. Apparently you were not aware of Flew's writing or influence. It is not only a major big deal for atheists, but the result of Christian apologists and that just ruins the decade for some. He left the reservation so now you attack his person in a most dignified, scholarly and scientific manner. So you think you can discredit the mental process that led him to discard atheism over the years can be dismissed by his age? Hmmm. How old are you?

This doesn't even make any sense. Of course he [Darwin] meant what he wrote.

Then you'll enjoy some of the ALS classics:

There are more if you want.

[PatrickHenry]

Permit me to explode yet another fraudlulent example of shameless creationoid quote-mining, the part presented as being a legitimate quote is in blue:

My dear Lyell,

You seemed to have worked admirably on the species question; there could not have been a better plan than reading up on the opposite side. I rejoice profoundly that you intend admitting the doctrine of modification in your new edition; nothing, I am convinced, could be more important for its success. I honour you most sincerely. To have maintained in the position of a master, one side of a question for thirty years, and then deliberately give it up, is a fact to which I much doubt whether the records of science offer a parallel. For myself, also, I rejoice profoundly; for, thinking of so many cases of men pursuing an illusion for years, often and often a cold shudder has run through me, and I have asked myself whether I may not have devoted my life to a phantasy. Now I look at it as morally impossible that investigators of truth, like you and Hooker, can be wholly wrong, and therefore I rest in peace. Source: HERE.

Observe the several indicia of fraudulent quote-mining: First, the alleged quote begins in mid-sentence. Second, the alleged quote has no source to check it out (easily remedied, however). Third, Darwin is really saying that he is delighted to have other experts agree with him. Fourth, the creationoids never seem to tire of trying to quote Darwin as their "evidence" against evolution. Tragic behavior.