Posted on 06/04/2006 5:02:02 PM PDT by blam
Evolving genes may not size up brain
Bruce Bower
Two gene variants previously proposed as contributors to the evolution of human brain size exert no influence on brain volume in people today, a new report indicates. If these particular genes indeed spread quickly by natural selection, that process might have been spurred by the genes' effects on reproductive organs or other tissue outside the brain, say neurologist Roger P. Woods of the University of California, Los Angeles and his colleagues.
Prior research had indicated that a now-common variant of a gene called microcephalin originated 37,000 years ago and that a variant of a gene known as ASPM arose about 5,800 years ago (SN: 9/24/05, p. 206: Available to subscribers at http://www.sciencenews.org/articles/20050924/note16.asp).
Mutations in both of these genes have been linked to microcephaly, a disease that causes unusually small head size and mental retardation.
Woods' team used magnetic resonance imaging to measure the brain volumes of 120 healthy men and women from a variety of racial and ethnic backgrounds. Analysis of blood samples from each participant identified those who had inherited the common microcephalin and ASPM variants and those with either of two other versions of each gene.
After accounting for brain-size differences between the sexes and among ethnic groups, the researchers found that no specific gene variant regularly appeared in individuals with especially large or small brain volumes. The team reports the findings in the June 15 Human Molecular Genetics.
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Bruce Bower
Two genes already known to influence brain size have undergone relatively recent, survival-enhancing modifications in people and appear to be still evolving, a research team reports.
Specific variants of these genes have spread quickly by natural selection, say Bruce T. Lahn of the University of Chicago and his colleagues, who published separate reports on each gene in the Sept. 9 Science.
The researchers examined DNA from 1,186 adults representing 59 populations worldwide and determined the frequency of specific variants of the two genes called microcephalin and ASPM.
A variant of microcephalin originated roughly 37,000 years ago and now appears in 7 of 10 people, the scientists conclude from comparisons of the gene's sequence for the different groups. Populations outside of sub-Saharan Africa most frequently possess this modified gene.
A distinctive ASPM variant arose approximately 5,800 years ago and now shows up in 3 of 10 people. It occurs most often in Europeans, North Africans, Middle Easterners, and South Asians.
The functions of these particular DNA alterations, including any potential influence on intelligence or reasoning, remain unknown.
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Let me know when they figure out why I'm so myoptic, after all these years of evolution.
I think you're onto something. ;')
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Of course not, silly! A bigger brain would be squished up against the inside of the head!
Proctocephalin is a mighty gene [or jinn?] - I have been observing its action for as long as I could remember, and have read about more examples of it than I could care to number. It strikes high and low [most recently with the Senate version of the immigration bill], but there are no known ways of suppressing it.
exactly! What a nonsense conclusion of that article.
Just because some genes used to cause a bigger brain, doesn't mean that with the current brainsize, genetics and anatomy they still have their original funtion.
The fact remains that without ASM our brains become small.
The genes probably follow rather than dictate structure and function. The DNA is not needed for normal day to day function of the cell and is certainly not the seat of the cellular mind. That would be in the cell wall. As evidence note the normal function of the red blood cells that do quite well for a couple of months until something needs repair. That is when the DNA comes in: building and repair.
Well, they found out not very long ago that very smart children's brains grow faster than other brains, but then prune back more. Maybe they need to prune back so they can fit.
I assume they must prune back less important stuff because the kids grow up to be very smart adults.
Occasionally they discover that ordinary people have skulls filled mostly with fluid, their brain matter severely compressed. Do we really know essentially how the brain "produces" thought?
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Note: this topic is from June 4, 2006. |
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