Human brain still evolving

[LucidDreamer]

I'm asking you to put up or shut up' date=' Lucid. You have accused the report-writer at Howard Hughes of unprofessional conduct.

 

Show the passage at fault, or retract your accusation.

 

You cast aspersions on someone who writes press releases for HHMI. It would be unworthy and unscientific of him/her to put a value judgement bias on these alleles.

 

If you can show that the article is actually at fault, fine. Convince me by showing me. I will write to the guy's boss and let them know that the press release was written with an unscientific slant. In a case like this with high visibility that would be a serious screwup and the writer should be held accountable (or the editor who cleared the release)

 

If you cannot show this, then your accusation is unfounded and morally you should retract it.

 

so lets hear how you substantiate that the term "superiority" with its value connotations is "IMPLIED" in the actual HHMI press release that Skye linked.

 

I am happy either way. if you can prove your point, fine. if you cannot prove it and wish to retract, fine. no problemo either way.

[/quote']

People have misunderstood what I was trying to say before, and this must be another example. It's probably my ffault for not being clear enough. I am not accusing the author of that journal of unprofessional conduct. In fact if I had his job I would probably report it in about the same way. He is just reporting what the scientist found and the scientists opinons about the relevancy of what he found. It's the scientist that I am a accusing of making unsubstatiated claims about the relatedness of these two genes to culture and civilization and that the only means that the variations could arise is through specific natural selection.

[Martin]

It's the scientist that I am a accusing of making unsubstatiated claims about the relatedness of these two genes to culture and civilization and that the only means that the variations could arise is through specific natural selection.

 

OK, I understand a lot better. So what quote do you have from the scientist where he claims the following?

 

1. the two genes (or alleles, variants) have a proven relation to culture and civilization

 

2. the only way these alleles (particular variants) could "arise" is through some specified natural selection process.*

 

Please quote Bruce Lahn---he is the scientist in this case---to show us that HE REALLY DOES MAKE THE CLAIMS which you say you are accusing him of making.

 

Or, if you cannot find quotes from Lahn that actually make those two claims, then of course retract your accusation.

 

You understand, Lucid, that I need actual words from Lahn. More words from you will not suffice. Because i had the impression that Lahn CAREFULLY AVOIDED claiming anything like what you say. So please show me that I was mistaken by pasting in where he says 1 and 2..

 

*not quite sure what you mean by "arise". Different versions of a gene first occur, AFAIK, by mutation. they then may SPREAD through a population by various mechanisms some of which are selection, but it takes work to actually determine WHAT selection, and what selective advantage, if any, is responsible. the same gene can have several seemingly unrelated expressions and there may be several candidates for a selection mechanism, that have to be sorted out by further study. I think by "arise" you may mean spread, and you think that Lahn has claimed to know that the genes spread because of SOME SPECIFIED selection mechanism which he has determined. Show me where he says that please.

[Martin]

Dating method for the ASPM gene

 

time since most recent common ancestor = 2(T/D)*L

 

T=estimated number of mutations per base in the sequence being studied since a theoretical most recent common ancestor

D=estimated number of mutations per base in the gene compared to a chimp homolog

L=estimated time since chimps and humans diverged

 

=2(4.2x10^-6/0.00865)*6 million years

=5826 years.

 

 

So far we have not had many interesting posts on this thread. this one of Skye is extremely interesting. It describes the clock which lets them calculate that that one allele originated 5800 years ago. It is really ingenious.

 

On a geneticist/biologist blog today I saw where someone calculated that for that allele to spread all over europe and asia in that short a time it MUST HAVE CONFERRED APPROXIMATELY 5 TO 8 PERCENT REPRODUCTIVE ADVANTAGE!!!! (of some kind' date=' in some category as yet undetermined---one gene can effect various parts and cause various selective advantages or disadvantages)

 

AFAIK nobody is claiming to have proven what selective advantage was operating (there is just speculation about what that might be) but this one commenter on the blog calculated that whatever type advantage it was, it must have been a whopping big 5 percent one in order to explain the rapid spread. They have their routine formulas for these things, and a certain amount of experience.

 

HERE ARE THOSE BLOG LINKS brought up from a few posts back

more links about this:

this is from a blog called GENE EXPRESSION used by genetics and bio people:

http://www.gnxp.com/blog/2005/09/this-is-bruce-lahns-brain-on-aspm-and.php

(I found some of the comments, 82 so far, interesting---had an inside profession flavor)

 

 

here are two articles in the journal Science

http://www.sciencemag.org/content/current/#researcharticles

(scroll about 1/3 of the way down the page)

 

many articles on Google News

http://news.google.com/news?hl=en&ned=us&ie=UTF-8&ncl=http://www.washingtonpost.com/wp-dyn/content/article/2005/09/08/AR2005090801254.html

 

GENETICS AND PUBLIC HEALTH BLOG has a bit on it

http://www.aboutweblogs.com/genetics/item/1731

(with links to several other articles about genetic effects)

 

Has anybody checked out the comments on Gene Expression blog?

Hot topic. Good to see professional biologist reaction.

[LucidDreamer]

OK' date=' I understand a lot better. So what quote do you have from the scientist where he claims the following?

1. the two genes (or alleles, variants) have a proven relation to culture and civilization[/quote']

I didn't say he said that there was a proven relationship; that's why I used the word implied. I am simply reposting here, but I will paste it again if you like.

Their statistical analysis indicated that the Microcephalin haplogroup D appeared about 37,000 years ago, and the ASPM haplogroup D appeared about 5,800 years ago - both well after the emergence of modern humans about 200,000 years ago. “In the case of Microcephalin, the origin of the new variant coincides with the emergence of culturally modern humans,” said Lahn. “And the ASPM new variant originated at a time that coincides with the spread of agriculture, settled cities, and the first record of written language. So, a major question is whether the coincidence between the genetic evolution that we see and the cultural evolution of humans was causative, or did they synergize with each other?”

Definition of synergy: working better together than separately.

 

He gave two options: One is where there was a causative nature or one where they both improved each other. Either way, I think it implies that there is a relation to culture and civilization.

 

2. the only way these alleles (particular variants) could "arise" is through some specified natural selection process.*

"Their analysis indicated that for each of the two genes, one haplogroup occurs at a frequency far higher than that expected by chance, indicating that natural selection has driven up the frequency of the haplogroup." From the article provided.

From Lahn:""Here we have two microcephaly genes that show evidence of selection in the evolutionary history of the human species and that also show evidence of ongoing selection in humans."

He just used the word selection, but I think it's obvious that means natural selection.

[LucidDreamer]

delete

[Martin]

[[i didn't say he said that there was a proven relationship; that's why I used the word implied.]]

 

Logical implication is proof. Maybe you would like to accuse Lahm of TACITLY SUGGESTING some connection.

 

[[Quote:

Their statistical analysis indicated that the Microcephalin haplogroup D appeared about 37,000 years ago, and the ASPM haplogroup D appeared about 5,800 years ago - both well after the emergence of modern humans about 200,000 years ago. “In the case of Microcephalin, the origin of the new variant coincides with the emergence of culturally modern humans,” said Lahn. “And the ASPM new variant originated at a time that coincides with the spread of agriculture, settled cities, and the first record of written language. So, a major question is whether the coincidence between the genetic evolution that we see and the cultural evolution of humans was causative, or did they synergize with each other?”]]

 

SOMEBODY, LAHN OR THE JOURNALIST, GOOFED HERE BECAUSE THIS IS INCOMPLETE. The major question is whether this coincidence in time is causative, or synergistic (a kind of reciprocal causal relation) OR NOT causal, or synergistic. Lahn has not yet demonstrated a connection. he has only the suggestive evidence of simultaneity----that time coincidence.

 

IF YOU LOOK IN HIS SCHOLARLY PAPERS i think that will be clear----he is NOT claiming to have shown a causal, or synergistic, connection.

 

Too bad that did not come through clearly in the press release.

 

 

[[Quote:

"Their analysis indicated that for each of the two genes, one haplogroup occurs at a frequency far higher than that expected by chance, indicating that natural selection has driven up the frequency of the haplogroup." From the article provided.

From Lahn:""Here we have two microcephaly genes that show evidence of selection in the evolutionary history of the human species and that also show evidence of ongoing selection in humans."

 

He just used the word selection, but I think it's obvious that means natural selection.]]

 

I am glad to see quotes. I think you misinterpret them. what this means

"Here we have two microcephaly genes that show evidence of selection in the evolutionary history of the human species and that also show evidence of ongoing selection in humans."

 

is that he sees evidence of SOME selection process, so far they have not determined what it is (the same allele can confer diverse advantages, good knee joints, resitance to measles, large brain (if that is a help) and they need to study this some more to say WHAT selection process.

 

One idea is that the selection mechanism might have to do with brain function where some (so far unproven) advantage comes from that. But he does not claim to have distinguished a SPECIFIC selection process.

 

========================

 

Lucid, the reason I am pretty sure you are wrong

1. in inserting the value-laden "superiority" concept into discussion and blaming it on Lahn

2. in accusing Lahn of making unsubstantiated claims of having identified a specific selection mechanism to explain the rapid spread

3. in accusing Lahn of claiming to have established a connection to culture and civilization

 

is that he is a smart competent scientist and not likely to do any of that, plus I myself see the opposite. Maybe in some writing of his I havent seen he DOES assert the things you say, in which case he is stupider than i thought.

 

1. I see him being careful NOT to use value terms like "superiority". you brought that in and quite unfairly accused either Lahn or the journalist of being responsible

 

2. what scientists like is to have more problems to work on so they can request grants to do more studies! those guys are saying explicitly they have NOT established the selection mechanism. What I see them doing now is conjecturing and speculating and hypothesizing and looking forward to the next course of the meal, when they get to determine what it really is.

 

3. What I see Lahn say is that because of that coincidence with the startup of cities and agriculture etc one can speculate that one possible selective advantage mechanism had something to do with that. It would be very interesting to prove something like that. It is a big interesting question if there is some recipocal causality or NOT. But it will take years of research to decide that one. AFAIK this is not something that Lahn is claiming is already proven! All he has is stats on the spread of an allele or two, and some ideas to test by future research. The whole point, one could say, of what he announced last week is that it presents some great questions to work on.

 

I can see that if you still want to criticize someone about what you think they tacitly or openly suggested then you will probably end up having to go to the library and reading Lahn's actual articles in SCIENCE magazine. That is probably the only way to make sure what he and his co-authors REALLY ARE SAYING.

 

Are you interested? I will get the issue and page numbers.

[Martin]

Here are the real papers that all the fuss is about

 

Microcephalin, a Gene Regulating Brain Size, Continues to Evolve Adaptively in Humans

Patrick D. Evans, Sandra L. Gilbert, Nitzan Mekel-Bobrov, Eric J. Vallender, Jeffrey R. Anderson, Leila M. Vaez-Azizi, Sarah A. Tishkoff, Richard R. Hudson, and Bruce T. Lahn

Science 9 September 2005: 1717-1720.

 

Ongoing Adaptive Evolution of ASPM, a Brain Size Determinant in Homo sapiens

Nitzan Mekel-Bobrov, Sandra L. Gilbert, Patrick D. Evans, Eric J. Vallender, Jeffrey R. Anderson, Richard R. Hudson, Sarah A. Tishkoff, and Bruce T. Lahn

Science 9 September 2005: 1720-1722.

 

 

Here is a way to eavesdrop on what biologists are saying NOT IN PUBLIC about this, these are haloscan comments from Genetics Expression blog.

In the private comments among colleagues you get a different side and perhaps somewhat less careful, more speculative. but these are not published claims, they are more casual conversation guesses.

 

http://www.haloscan.com/comments/raldanash/112621514101868344/#352755

 

http://www.haloscan.com/comments/raldanash/112621514101868344/#352831

[LucidDreamer]

Martin, I am totally flabbergasted. I provided exactly what you asked for. I provided a quote where he specifically claims a relationship to culture and civilization and you claim somebody must have goofed and misrepresented him. Then I provide another quote where he says that the alleles arose through natural selection, and you say that doesn't count because I once used the word specific. My use of the word specific was not intended to indicate that he claimed to know the exact mechanism, but from the comments that I have read about him he seems to believe that they are specifically related to culture and civilization and that natural selection has acted on these two genes in this capacity.

 

Now, it could be that I am totally insane or a complete idiot and I have totally misunderstood the two articles that I read about the subject, but I think they were pretty clear and either somebody is misrepresenting him or he is really, indirectly or directly, proposing exactly what I have said. Now, I want to clarify one last thing. I don’t necessarily disagree with his position, which I am only deducing from two articles that I read and a few quotes. I totally agree for one thing, that natural selection was probably involved in the spread of the allele that arose 5800 years ago, assuming that his research about the emergence of allele is good.

 

You claim that I have said terrible and unjust things about both a reporter and then a scientist, but I feel I have only repeated what I read on the article provided with very minimal induction. I did say that it is unscientific to suggest that these genes are related to culture and civilization because they are as yet unsubstantiated, and I stand by that. Scientists say all kinds of things like that all the time because they like to believe that the work that they put their heart and sole into is extremely significant, which is only human nature. I am only trying to differentiate what his research really indicates from what he would like to believe and his opinions. I can’t fathom what exactly made you turn on me like that, but I can only tell you that I very much enjoy and appreciate all of the many excellent posts you have made on this forum. I will indeed read his papers when I get a hold of them.

[zyncod]

Here is a way to eavesdrop on what biologists are saying NOT IN PUBLIC about this, these are haloscan comments from Genetics Expression blog.

 

This is not how you see what biologists are saying about microcephalin. The way that you actually see what they are saying is to wait for further papers to come out about this topic. I can understand the public's complete lack of patience, but you've all waited thousands of years even to hear about microcephalin. You can wait a year or two longer to get some rational discourse about this topic.

[Martin]

I agree with several things you say, Lucid, if I understand you.

...Now' date=' I want to clarify one last thing. I don’t necessarily disagree with his position, which I am only deducing from two articles that I read and a few quotes. I totally agree for one thing, that natural selection was probably involved in the spread of the allele that arose 5800 years ago, assuming that his research about the emergence of allele is good.

...[/quote']

 

I agree with him that some kind of adaptive natural selection was probably responsible for the spread of both alleles. Also that we dont know WHAT was being selected, in each case. An allele might confer extra ability to digest furry mammoth meat, or a tolerance for dank smoky caves, as well as being related to brain volume.

 

If you agree that at least one allele (the ASPM one) probably spread by some still undetermined selection mechanism, I agree with you.

 

Not enough research has been done to indicate what kind of adaptive advantage the alleles provide. Certainly not enough research has been done to establish a firm link to the appearance of cities etc. I am of the strong opinion that it would be unscientific of Lahn to be claiming now that he already knows what the advantage was or that he has established a causal (or synergic) relation between that and civilization!

 

I would say that his research does raise a major question, which is WHETHER OR NOT there is some causal (one way or two way) connection between the spread of the allele and those historical developments (cities, agriculture) that happened around the same time.

 

BTW I dont think the issue of one-way versus two-way causality is major, what I see as the big question is whether there is any causal link at all.

 

Anyway I think it would have been grossly unscientific for Lahn to claim that a causal link has already been established. That is a matter for some very interesting future research. As things are now it has not even been established that the alleles contribute to any type of mental function that could, in turn, contribute to some of those historical changes. So I agree with your general tenor here, if not with the exact words:

 

... I did say that it is unscientific to suggest that these genes are related to culture and civilization because they are as yet unsubstantiated, and I stand by that...

 

Actually let's change "they are" to "that is" because the genes are substantiated---all sequenced and found in the population and frequency measured etc. It is the relation to culture etc that is unsubstantiated. And "suggest" is pretty vague---what some statement SUGGESTS to different listeners depends on what they want to hear and how SUGGESTIBLE they are. So let's say assert---then with that clarification we have agreement

 

... I did say that it is unscientific to assert that these genes are related to culture and civilization because this is as yet unsubstantiated, and I stand by that...

 

I hope you agree with this trivial clarification and will stand by this! I have said it and do say it and certainly stand behind it myself.

 

I also very much approve and am glad about your intention:

I will indeed read his papers when I get a hold of them

 

Maybe your setting a good example will get me to make an effort to look at the 9 September issue of Science

 

Eventually, when someone sees the actual Lahn articles we will get a less ambiguous quote that makes it clearer what he is asserting as proven and what he is not, at least as yet, asserting.

 

For the time being I will assume that this is a garbled misquotation:

 

"So, a major question is whether the coincidence between the genetic evolution that we see and the cultural evolution of humans was causative, or did they synergize with each other?"

 

The major question which everybody sees here is whether or not there was some (one-way or two-way) causal connection that can help explain the coincidence in time.

 

It would not make sense, I think, for him to be pretending that this big question has already been settled and that what is left is the (relatively trivial) issue of whether it was one-way causality or some two-way synergistic connection.

 

If there turns out to have been any causal link, then I would say that it is very likely to have been synergistic----that is, if the genes helped get people started doing agriculture and cities, then in a kind of feedback or reciprocity the cities in turn provided circumstances in which those genes were even more advantageous----the idea would be "the spread of the allele promoted cities and the cities in turn promoted the spread of the allele". My guess would be if there is any causality at all, then it is working both ways. So that is not a big issue, as I see it.

 

When I read that quotation, which your response suggests to me may have been garbled, I took it to mean this:

 

A major question is whether or not there is a causative (one or two-way) connection between the genetic evolution that we see and the cultural evolution of humans

 

I think that is one fair construction of the quote you cited, although I wish it had been worded more clearly.

[Martin]

This is not how you see what biologists are saying about microcephalin. The way that you actually see what they are saying is to wait for further papers to come out about this topic. I can understand the public's complete lack of patience, but you've all waited thousands of years even to hear about microcephalin. You can wait a year or two longer to get some rational discourse about this topic.

 

Hi zyncod, I like your reaction which seems very sensible. Agreed it's very premature to be speculating about what this finding means. One can only guess as to what future research will turn up.

 

As I understand it, and please correct me if I am wrong, all we know is that a couple of alleles probably spread rapidly in a certain time frame. One of them, in particular, spread over much of the earth and got into many regions (though not all) in a matter of a few 1000 years----like 6000 years.

 

It is reasonable, again correct me if I am mistaken, that such a rapid wide spread could only have happened if the expression was in some way ADAPTIVE. We dont know what the adaptiveness was, but we can say it probably wouldnt have spread so fast if it hadnt conferred some reproductive advantage on the bearer and had some selection mechanism going for it.

 

That is all I get from the published stuff, the HHMI press release, etc. And this is all that Lahn is saying in public, as far as I can tell.

 

he does point out the coincidence in time with some historical developments, which does raise a major unresolved question.

 

Do you agree?

 

As for listening in to the backroom scuttlebut in the Human Genetics department, I think that is fun. A lot of those guys are obviously scientists, maybe all, but given it is not published but is only informal off-the-record in-group blog-speculation, I'd say they speak their minds pretty freely. I will repost the links to that discussion thread:

 

http://www.haloscan.com/comments/raldanash/112621514101868344/#352755

 

http://www.haloscan.com/comments/raldanash/112621514101868344/#352831

 

I happened to find another Bruce Lahn link:

http://www.genes.uchicago.edu/fri/lahnres.html

 

Here is the PubMed online abstract of the ASPM article

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16151010&itool=iconabstr&query_hl=1

 

Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens.

 

Mekel-Bobrov N, Gilbert SL, Evans PD, Vallender EJ, Anderson JR, Hudson RR, Tishkoff SA, Lahn BT.

 

Howard Hughes Medical Institute, Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA.

 

"The gene ASPM (abnormal spindle-like microcephaly associated) is a specific regulator of brain size, and its evolution in the lineage leading to Homo sapiens was driven by strong positive selection. Here, we show that one genetic variant of ASPM in humans arose merely about 5800 years ago and has since swept to high frequency under strong positive selection. These findings, especially the remarkably young age of the positively selected variant, suggest that the human brain is still undergoing rapid adaptive evolution."

 

Here is the abstract for the other paper, the Microcephalin one:

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16151009&itool=iconabstr&query_hl=1

 

Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans.

 

Evans PD, Gilbert SL, Mekel-Bobrov N, Vallender EJ, Anderson JR, Vaez-Azizi LM, Tishkoff SA, Hudson RR, Lahn BT.

 

Howard Hughes Medical Institute, Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA.

 

"The gene Microcephalin (MCPH1) regulates brain size and has evolved under strong positive selection in the human evolutionary lineage. We show that one genetic variant of Microcephalin in modern humans, which arose approximately 37,000 years ago, increased in frequency too rapidly to be compatible with neutral drift. This indicates that it has spread under strong positive selection, although the exact nature of the selection is unknown. The finding that an important brain gene has continued to evolve adaptively in anatomically modern humans suggests the ongoing evolutionary plasticity of the human brain. It also makes Microcephalin an attractive candidate locus for studying the genetics of human variation in brain-related phenotypes."

[Martin]

http://hmg.oxfordjournals.org/cgi/content/full/13/11/1139

 

Reconstructing the evolutionary history of microcephalin, a gene controlling human brain size

 

Patrick D. Evans1,2, Jeffrey R. Anderson1, Eric J. Vallender1,2, Sun Shim Choi1 and Bruce T. Lahn1,*

1Howard Hughes Medical Institute, Department of Human Genetics and 2Committee on Genetics, University of Chicago, Chicago, IL 60637, USA

Received February 24, 2004; Accepted March 25, 2004

 

Abstract:

"The defining process in the evolution of primates and particularly humans is the dramatic expansion of the brain. While many types of genes could potentially contribute to this process, genes that specifically regulate brain size during development may be especially relevant. Here, we examine the evolution of the microcephalin gene, whose null mutation in humans causes primary microcephaly, a congenital defect characterized by severe reductions in brain size without other gross abnormalities. We show that the evolution of microcephalin's protein sequence is highly accelerated throughout the lineage from simian ancestors to humans and chimpanzees, with the most pronounced acceleration seen in the early periods of this lineage. We further demonstrate that this accelerated evolution is coupled with signatures of positive selection. Statistical analysis suggests that about 45 advantageous amino acid changes in microcephalin might have fixed during the 25–30 million years of evolution from early simian progenitors to modern humans. These observations support the notion that the molecular evolution of microcephalin may have contributed to brain expansion in the simian lineage leading to humans. We have recently shown that ASPM, another gene linked to primary microcephaly, experienced strong positive selection in the ape lineage leading to humans. We therefore propose that genes regulating brain size during development may have the general propensity to contribute to brain evolution in primates and particularly humans."

 

Going by the page numbering where it was published, the journal Human Molecular Genetics, this is a 6 page paper. As a sample, here is the introductory paragraph:

" As a species, Homo sapiens is distinguished by its highly advanced mental capacity (1). A key biological basis for this is believed to be the enormous brain size of humans relative to other extant taxa (2–4). This is particularly true for the cerebral cortex, the region of the brain most prominently involved in higher cognitive functions (5,6). Indeed, there is a general correlation across taxa between the level of encephalization and cognitive complexity (7), which has led researchers to utilize anatomical dimensions of the brain, especially the size of the cerebral cortex, as proxies for cognitive abilities of extant and extinct species. More recently, discussions of brain evolution have moved from the traditional realms of anatomy, physiology and behavior to the domains of genes and genome organization (8,9). Of particular interest to researchers is the identification of specific genes whose evolution at the DNA sequence level may have contributed to the evolutionary expansion of the brain..."

 

the two recent articles in 9 September Science are not, AFAIK, available anywhere online free. However they are each only about 3 pages (going by the journal's pagination). maybe someone will scan them or post them at website sometime. in the meantime this 6 page article is free for downloading and gives a firsthand idea of what Lahn and coworkers are doing. It has charts and data and some technical detail of how their studies are conducted.

 

=================

Bruce Lahn heads the Lahn Lab at HHMI/U.Chicago and his webpage

http://www.genes.uchicago.edu/fri/lahnres.html

has a statement of research goals. Here is a sample:

Bruce Lahn, PhD.

Asst. Professor

Howard Hughes Medical Institute

Department of Human Genetics

Department of Molecular Genetics and Cell Biology

 

Click here to visit Lahn lab home page

 

"Our laboratory is interested in developing and applying innovative genetic approaches to the study of mammalian development and evolution, with an emphasis on the brain. The following is a sampling of our diverse research interests:

 

1. Genetic basis of human brain evolution

One of the ultimate quests in biology is to understand the molecular basis underlying the distinct cognitive capacity of the human brain. Our lab investigates this question by an evolutionary approach, where we systematically compare sequences and expression patterns of brain-related genes between humans and other mammals. The techniques we employ include high-throughput sequencing and microarray-based expression analysis. Through these comparative studies, we have identified candidate “human-ness” genes, which appear to have undergone distinct evolutionary changes in the human lineage relative to other mammalian lineages. Through further investigation of these genes, we hope to uncover genetic basis that underlie unique functional properties of the human brain...."

[Martin]

http://hmg.oxfordjournals.org/cgi/content/full/13/5/489

Adaptive evolution of ASPM, a major determinant of cerebral cortical size in humans.

Evans PD, Anderson JR, Vallender EJ, Gilbert SL, Malcom CM, Dorus S, Lahn BT.

Howard Hughes Medical Institute, Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA.

 

"A prominent trend in the evolution of humans is the progressive enlargement of the cerebral cortex. The ASPM (Abnormal spindle-like microcephaly associated) gene has the potential to play a role in this evolutionary process, because mutations in this gene cause severe reductions in the cerebral cortical size of affected humans. Here, we show that the evolution of ASPM is significantly accelerated in great apes, especially along the ape lineages leading to humans. Additionally, the lineage from the last human/chimpanzee ancestor to humans shows an excess of non-synonymous over synonymous substitutions, which is a signature of positive Darwinian selection. A comparison of polymorphism and divergence using the McDonald-Kreitman test confirms that ASPM has indeed experienced intense positive selection during recent human evolution. This test also reveals that, on average, ASPM fixed one advantageous amino acid change in every 300,000-400,000 years since the human lineage diverged from chimpanzees some 5-6 million years ago. We therefore conclude that ASPM underwent strong adaptive evolution in the descent of Homo sapiens, which is consistent with its putative role in the evolutionary enlargement of the human brain."

 

this is another ready to download PDF and print in case anyone is interested. It is also about 6 pages. I wish the two that just appeared in Science were available free, but couldnt find them.