NYT: Human brain still evolving

[Martin]

http://www.nytimes.com/2005/09/08/science/08cnd-brain.html?ei=5094&en=7f83ee9b96d40611&hp=&ex=1126238400&adxnnl=1&partner=homepage&adxnnlx=1126224003-zyBKE45IEICeBUIKvUHFdg

 

"Two genes involved in determining the size of the human brain have undergone substantial evolution in the last 60,000 years, researchers say, suggesting that the brain is still undergoing rapid evolution...

 

...The new finding, reported by Bruce T. Lahn of the University of Chicago and colleagues in the journal Science, could raise controversy because of the genes' role in determining brain size. New versions of the genes, or alleles, as geneticists call them, appear to have spread because they enhanced the brain's function in some way, the report suggests, and they are more common in some populations than others..."

[Martin]

this news event (which is of some importance in human genetics) was flagged at about the same time by Skye, who started a thread

 

http://scienceforums.net/forums/showthread.php?t=14364

 

and indicated an important guideline for discussing the scientific issues in a value-neutral way

 

They found that, for each gene, a particular goup of polymorphisms had been positively selected for. The actual function of the genes isn't known with certainty, and the authors are keen to avoid any ubermensch talk.

[Martin]

Here are some possibly useful links:

 

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

free download of complete Lahn ASPM article from Human Molecular Genetics

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

 

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

free download of complete Lahn Microcephalin article from Human Molecular Genetics

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

 

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15620360&itool=iconabstr&query_hl=5

abstract of Lahn article

 

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16151009&query_hl=5

abstract of Lahn Microcephalin article in 9 Sept Science journal.

 

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16151010&query_hl=5

abstract of Lahn ASPM article in 9 Sept Science

 

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

 

Here is a press release from the HHMI where Lahn has his lab. the PR journalist, or public information writer, assigned to the job may have garbled or misquoted Lahn, so be careful about putting too much weight on the press release (or the NY Times article either!)

 

http://www.hhmi.org/news/lahn4.html

 

http://www.hhmi.org/research/investigators/lahn.html

 

the only way to tell what Lahn and his colleagues claim or do not claim to have discovered is to read what they publish in Human Molecular Genetics, or the journal Science.

[Callipygous]

were we under the arrogant assumption that humans were past evolution?

[Martin]

were we under the arrogant assumption that humans were past evolution?

 

Hi Callipygous, several people were put off by the headline. I think the point of the article was not merely that brain is still evolving. the point is that by geneticist standards the evolution has been rapid in the case of two particular alleles. One of them, a variant of the ASPM gene has spread thru much of the world population amazingly fast (since roughly 3800 BC).

 

Since most newspaper readers don't have a clear perspective on the speed with which alleles spread. So the headline writer had a problem, he should have said something like

 

Brain evolving unexpectedly FAST

 

but I guess that wouldnt make sense----wouldnt be a good headline. So he said simply

Brain evolving

 

which is not the point

 

I have to go out, back and resume later

[Martin]

Callipygous, since i know you are OK with the math I will try to reproduce what Skye explained to me about how they calculate the time (5800 years ago) when ASPM began to spread

 

and also mention one other quantitative thing: IIRC a geneticist on a humangenetics blog said that for it to have spread in that short a time then it would have to have had a 6 percent reproductive advantage

 

(I will check that, maybe he said 4 to 8 percent or something like that.)

 

that means that someone with that allele will have on average 6 percent more grandchildren than someone with the other type.

 

that is the impressive thing. everything, like your liver and your eyes and your thumbs etc is always evolving but usually quite gradually and almost as it were by a DRIFT, like a boat drifting without wind.

 

but this rapid spread of an allele that could only happen with a strong selective PRESSURE is a different thing, which one doesnt necessarily expect.

 

this is all assuming that the result stands and is not overturned by subsequent research----and I hope i am explaining it essentially right.

 

Now how do they arrive at the estimate that this allele started spreading in the human population around 3800 BC, or about 5800 years ago.

Skye provide some arithmetic for that. Did you happen to see it? If so then I dont need to copy it here.

 

this was Skye's post:

http://scienceforums.net/forums/showthread.php?p=206175#post206175

 

it was #16 in his thread on this, I expounded it a little in post #17 to make the steps in the reasoning a bit plainer.

[Martin]

a lot of additional information in this geneticist blog

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

 

blog is called "Gene Expression"

 

there are some maps showing the distribution of ASPM,

extent of spread

 

this blog is where one of the posters estimated what selective pressure would be needed to drive that rapid a spread

 

Look at this map for the Microcephalin allele spread

http://www.gnxp.com/blog/uploaded_images/MCPH1-37,000-722163.JPG

 

Look at this map for the ASPM allele spread

http://www.gnxp.com/blog/uploaded_images/ASPM%20-%205,800-787176.JPG

 

 

here is more blog discussion

http://universalacid.blogspot.com/2005/09/human-brain-still-evolving.html

 

http://johnhawks.net/weblog/reviews/genetics/brain/lahn_2005_aspm_microcephalin_science.html

 

http://science.slashdot.org/article.pl?sid=05/09/09/003203&tid=191&tid=14

[CanadaAotS]

The real question is, what is this gene doing that gives a 6% better chance of producing offspring?

[Martin]

The real question is, what is this gene doing that gives a 6% better chance of producing offspring?

 

on average 6 percent more grandchildren

like 17 is roughly 6 percent more than 16

so take some historical period and some region and take 4 random peasants who have the variant gene

and 4 random peasants who have the ordinary usual version of the gene

 

and count their grandchildren (that survive various hardships, famines, wars, floods plagues whatever and themselves reach reproductive age) and you find that the 4 "variant" peasants have 17 grandchildren

and the 4 "usual" peasants have 16 grandchildren

 

or it averages out like that, with larger samples

I think that is what they mean by "reproductive fitness". Mokele or Skye can confirm if they are around.

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

 

OK so CANADA you have asked the big question!

 

I can't tell you because I am far from expert, but let's check the links to see if they still work

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

 

Go there, scroll down to the maps. Click on the maps to see the geograph. distribution of the gene-variants ("alleles")

 

RIGHT BELOW THE MAPS IT SAYS 'COMMENTS' right now it says "96 comments"

 

So click on that.

There you will see professional human genetics people SPECULATING about why the genes could spread so fast and why they would confer reproductive advantage. It is a mixed group, not all professionals and not all looking at the results in a cool skeptical way, but quite a few seem to be looking at the stuff scientificially and reasoning technically about it. You have to pick the ones that seem knowledgeable and reliable to you.

 

Anyway CANADA please read some of those 96 comments and tell me what catches your attention. I dont know any better way to respond to your questions. Those people are trying to figure out the answer just like we are. some are making risky guesses, some are reserving judgement, and so on.

[dragono]

Every organism is aways evolving, so why did we think we were different?

[Mokele]

Every organism is aways evolving, so why did we think we were different?

 

Not necessarily. If selection favors the middle value of trait which occurs in a range of values, then the mean value will remain the same and thus no real evolution has occured, at least at that locus / for that trait.

 

Also, humans have relaxed selection pressure so much that fast-evolving genes would be something of a suprise.

 

Mokele

[Pangloss]

I was just reading this morning the introduction to Russell and Norvig's famous "Artificial Intelligence: A Modern Approach" (generally considered the standard introductory textbook on AI), which was recently revised (2003), and came across this passage:

 

We now have data on the mapping between areas of the brain and the parts of the body that they control or from which they receive sensory input. Such mappings are able to change radically over the course of a few weeks, and some animals seem to have multiple maps. Moreover, we do not fully understand how other areas can take over functions when one area is damaged. There is almost no theory on how an individual memory is stored.

 

It seems to me that we may not know enough to know if the brain is evolving or not. But I suppose it's also reasonable to suggest that it seems to be doing so.

 

I'll have to think it over. (ar ar)

[Mokele]

It seems to me that we may not know enough to know if the brain is evolving or not.

 

Actually, we don't need to know how it works to tell if it's evolving. All we need to know is that certain genes are associated with the brain, an that those genes are changing faster than would be predicted by random effects, and their frequency increasing faster than one would expect from random processes. What they *do* is superfluous to theinvestigation, only that they're spreading and changing rapidly.

 

Mokele

[Martin]

Actually' date=' we don't need to know how it works to tell if it's evolving. All we need to know is that certain genes are associated with the brain, an that those genes are changing faster than would be predicted by random effects, and their frequency increasing faster than one would expect from random processes. What they *do* is superfluous to theinvestigation, only that they're spreading and changing rapidly.

 

Mokele[/quote']

 

Mokele, this is a bit off the OP topic, but has to do with what you say about proving that evolution is occuring in ways that fit the model.

 

there was this article in the Washington Post

http://www.washingtonpost.com/wp-dyn/content/article/2005/09/25/AR2005092501177.html?referrer=email&referrer=email

 

It says something that I find intriguing but that i dont completely understand.

 

By comparing populations of two related species, with known population sizes, one can apparently PREDICT the load of harmful mutations carried by one of the populations. How?

 

Apparently someone just did this with Chimps----they predicted the number of harmful mutations that should be present in the chimp population. This is a test of the evolutionary model. The model predicts a certain number. Then they counted and found that the prediction was RIGHT.

 

I would like to understand this better, in case anyone wants to explain it more completely than they do in this article. Here is a quote:

----quote----

If Darwin was right, for example, then scientists should be able to perform a neat trick. Using a mathematical formula that emerges from evolutionary theory, they should be able to predict the number of harmful mutations in chimpanzee DNA by knowing the number of mutations in a different species' DNA and the two animals' population sizes.

 

"That's a very specific prediction," said Eric Lander, a geneticist at the Broad Institute of MIT and Harvard in Cambridge, Mass., and a leader in the chimp project...

---endquote---

 

here is some blog discussion of the article:

http://pharyngula.org/index/weblog/comments/journalists_getting_it_right/

 

here is Eric Lander's MIT homepage:

http://web.mit.edu/biology/www/facultyareas/facresearch/lander.shtml

 

here is a related article in the Harvard Crimson:

http://www.news.harvard.edu/gazette/2005/09.15/11-chimp.html

[Mokele]

It sounds like a part of population genetics, but far in advance of the level at which I've been exposed to it. I can guess at the rudiments of the math behind it (mutation rates, genetic drift, selection pressures, etc), but I suspect the application to such a problem requires a computer.

 

Mokele

[mariabrenna]

do they ever randomly mutate human genes, trying to test for something that might correlate with increased fitness? For example, you said they discovered microcephalin and ASPM may affect brain size. Would they try to make a mutation that affected brain-size in a similiar fashion and test it?

 

also, how does one differentiate a gene that is evolving the human species versus just mutating a small population of the race?

[Mokele]

do they ever randomly mutate human genes, trying to test for something that might correlate with increased fitness? For example, you said they discovered microcephalin and ASPM may affect brain size. Would they try to make a mutation that affected brain-size in a similiar fashion and test it?

 

They do in flies and other animals, and fitness studies are actually rather common (though few are done via experimental manipulation, but rather taker advantage of existing natural variation). As for humans, no, since you can't make a test population, and we've altered out environment so much that it'd be hard to tell from observation if there's any effect.

 

also, how does one differentiate a gene that is evolving the human species versus just mutating a small population of the race?

 

Test around, see who has the gene.

 

Mokele

[Mayflower]

were we under the arrogant assumption that humans were past evolution?

 

I find it a bit arrogant to think that we are still evolving.

[lucaspa]

Here is a press release from the HHMI where Lahn has his lab. the PR journalist, or public information writer, assigned to the job may have garbled or misquoted Lahn, so be careful about putting too much weight on the press release (or the NY Times article either!) ... the only way to tell what Lahn and his colleagues claim or do not claim to have discovered is to read what they publish in Human Molecular Genetics, or the journal Science.

 

Good points! I also note that the the NY Times article claims the microcephalin allele appeared 50, 000 years ago and claim it is associated with "modern" humans. However, anatomically modern humans -- including present brain size -- were present 100,000 years ago. This raises skepticism in me whether the alleles have that much to do with brain size.

[lucaspa]

I find it a bit arrogant to think that we are still evolving.

We are mostly immune to evolution due to our technology and transportation. The technology negates natural selection by providing resources for everyone and compensating for traits -- such as poor eyesight -- that would be disadvantageous otherwise. Transportation means we have gene flow between most populations, which stops allopatric speciation.

 

However, HIV is causing the selection of individuals with alleles that confer immunity. Also, there are indications that 3 populations of humans are diverging and could, if the trend continues, form their own species.

 

Two of these are Andean and Himalayan highlanders. Data shows they have unique alleles for adaptation to living at the high altitudes. The question is how much they intermarry with lowlanders for gene flow. If they do not intermarry and become isolated in their unique climates, then over many more generations they could become reproductively isolated from the rest of humans -- which means they would be a new species of Homo.

 

The other is the !Kung. Data shows that marriage patterns are that genes do not flow into to !Kung but that a few !Kung intermarry outside the !Kung. So, they are already showing partial reproductive isolation by one of the early mechanisms -- mate selection. Since the !Kung live in the Kalahari, they have adpatations for living in a very arid climate. Two studies have demonstrated that !Kung have some unique alleles. Again, if this continues for many generations, we would have a new species of Homo.

 

Allopatric speciation like this is one of the major mechanisms of evolution. Transformation of an entire large population -- like H. sapiens is now -- is very rare. Instead, you get species splitting and the formation of new species in small populations that are isolated in new environments -- allopatric speciation.

[lucaspa]

do they ever randomly mutate human genes' date=' trying to test for something that might correlate with increased fitness? For example, you said they discovered microcephalin and ASPM may affect brain size. Would they try to make a mutation that affected brain-size in a similiar fashion and test it?

 

also, how does one differentiate a gene that is evolving the human species versus just mutating a small population of the race?[/quote']

1. How would you test a mutated gene? Testing of fitness requires the entire organism, in this case a human being. It would be illegal and immoral to form genetically engineered humans.

 

2. "mutating in a small population" is how most evolution happens. See my previous post and allopatric speciation. You are thinking of transforming the entire human population to a new species. This is called "anagenesis". It is very rare in evolution. Instead, what you nearly always see is "cladogenesis" where a small population is isolated -- either by geography or by ecology -- and face a different environment. Mutations that are neutral in the old environment are advantageous in the new. So there is directional natural selection to "fix" those alleles in the small population. Over the course of generations, those changes are enough to make the small population a new species.

 

Large populations that are adapted to their environment have stabilizing natural selection. Most mutations would be less adaptive than the existing alleles and get eliminated.

 

Everyone seems to think that increasing brain size in humans would be selected. I just don't see any selective pressure for increased brain size or intelligence. People with IQs of 80 earn adequate living (in evolutionary terms) and have just as many, or more, offspring than people with IQs of 180.

[Martin]

this is a very interesting post.

 

it makes me think that sometimes at SFN we have too small a "gene pool" or "breeding population". or not enough to be a critical mass.

 

I was preoccupied with something else. nobody else responded.

 

We are mostly immune to evolution due to our technology and transportation. The technology negates natural selection by providing resources for everyone and compensating for traits -- such as poor eyesight -- that would be disadvantageous otherwise. Transportation means we have gene flow between most populations' date=' which stops allopatric speciation.

 

However, HIV is causing the selection of individuals with alleles that confer immunity. Also, there are indications that 3 populations of humans are diverging and could, if the trend continues, form their own species.

 

Two of these are Andean and Himalayan highlanders. Data shows they have unique alleles for adaptation to living at the high altitudes. The question is how much they intermarry with lowlanders for gene flow. If they do not intermarry and become isolated in their unique climates, then over many more generations they could become reproductively isolated from the rest of humans -- which means they would be a new species of Homo.

 

The other is the !Kung. Data shows that marriage patterns are that genes do not flow into to !Kung but that a few !Kung intermarry outside the !Kung. So, they are already showing partial reproductive isolation by one of the early mechanisms -- mate selection. Since the !Kung live in the Kalahari, they have adpatations for living in a very arid climate. Two studies have demonstrated that !Kung have some unique alleles. Again, if this continues for many generations, we would have a new species of Homo.

 

Allopatric speciation like this is one of the major mechanisms of evolution. Transformation of an entire large population -- like H. sapiens is now -- is very rare. Instead, you get species splitting and the formation of new species in small populations that are isolated in new environments -- allopatric speciation.[/quote']

[Martin]

this is a very interesting post.

 

it makes me think that sometimes at SFN we have too small a "gene pool" or "breeding population". or not enough to be a critical mass.

 

I was preoccupied with something else. nobody else responded.

 

We are mostly immune to evolution due to our technology and transportation. The technology negates natural selection by providing resources for everyone and compensating for traits -- such as poor eyesight -- that would be disadvantageous otherwise. Transportation means we have gene flow between most populations' date=' which stops allopatric speciation.

 

However, HIV is causing the selection of individuals with alleles that confer immunity. Also, there are indications that 3 populations of humans are diverging and could, if the trend continues, form their own species.

 

Two of these are Andean and Himalayan highlanders. Data shows they have unique alleles for adaptation to living at the high altitudes. The question is how much they intermarry with lowlanders for gene flow. If they do not intermarry and become isolated in their unique climates, then over many more generations they could become reproductively isolated from the rest of humans -- which means they would be a new species of Homo.

 

The other is the !Kung. Data shows that marriage patterns are that genes do not flow into to !Kung but that a few !Kung intermarry outside the !Kung. So, they are already showing partial reproductive isolation by one of the early mechanisms -- mate selection. Since the !Kung live in the Kalahari, they have adpatations for living in a very arid climate. Two studies have demonstrated that !Kung have some unique alleles. Again, if this continues for many generations, we would have a new species of Homo.

 

Allopatric speciation like this is one of the major mechanisms of evolution. Transformation of an entire large population -- like H. sapiens is now -- is very rare. Instead, you get species splitting and the formation of new species in small populations that are isolated in new environments -- allopatric speciation.[/quote']

[Royston]

The Andean people although (from first hand experience) are not completely isolated they do indeed have a larger lung capacity to cope with the higher altitude and obviously lower oxygen levels.

 

In a documentary a few years back (the name escapes me) the residents of an Andean village played football against a group of physically fit westerners...needless to say the Andeans ran circles round them. Although you could argue this isn't really a controlled experiment (I will try and find links to this topic) it'll be interesting to see if these traits survive.

 

Having had the privelage of trekking through the Andes, the villages are becoming less isolated, most villages have access to transport / roads et.c and western influence can be seen pretty much anywhere you go. It's really a case of what takes precedence, preservation or westernisation. With the temptation of arguably better lives in 'the city' et.c and the effects that economic growth and western culture has on small settlements (predominantly negative effects) then I'm wondering if this will accelerate too much before we do see a new species of homo sapiens.

 

BRB

 

Here we go...

 

http://jeb.biologists.org/cgi/content/full/204/18/3151

[Severian]

I would have thought that the modern evolutionary trend would be towards smaller brains. It is definitely true that people who are successful academically (who you would suppose have larger brains) have fewer offspring than their small brained (McDonald's serving) neighbours. Of course, this was not true 60,000 years ago....