Will new gene discoveries substantiate bigotry? The ASPM gene

The explosion in DNA analysis can expose differences between us that affect our abilities and can be screened for before birth. There may be correlations with race but there are now questions as to whether the human races have statistical reality. This means that there can be more variation within the classical races than between them. It is now relatively well accepted that humans originated in Africa between 100 and 200 thousand years ago and that all non-Africans left the continent less than 70,000 years ago as a very small group. We are a very young species that has almost gone extinct more than once. We populated the world very rapidly displacing earlier hominids such as homo erectus and Neanderthal. There was something different about us that gave us a significant advantage. We are on the verge of identifying just which genes made us human and which variants of these genes are “best”. Such identifications will allow “inferior” individuals to be identified in the womb and eliminated. It also may result in us being categorized at birth as to our future potential and segregated into different groups based on these determinations.

Many “intelligence” genes are identified by examining the DNA of individuals with mental handicaps. One such example is the ASPM gene which was identified as the causative agent in inherited microcephaly.
http://eprints.iisc.ernet.in/archive/00000196/03/629.pdf

It is claimed as described below, that this gene has undergone recent rapid evolution suggesting that it is very important to human development. Also, not all humans have the same variants of the gene. Does this affect IQ? No, as described in the article from Science magazine. http://www.sciencemag.org/cgi/content/full/314/5807/1872 and the variations in this gene in the “normal” population don’t seem to correlate with brain size. Some mutations of the ASPM gene do cause a significant decrease in brain size resulting in microcephaly but other genetic variation seen in people with normal brain size don’t seem to mater. There are many mutations that while different in genetic sequence make no change in phenotype of gene function.

However, there must be genetic control of intelligence, the genes will be discovered and we will probably discriminate. Its only human.



Excerpts from http://www.futurepundit.com/archives/001892.html
Bruce Lahn and collaborators have discovered signs of strong selective pressure in primates on a gene that affects brain size.
The researchers, led by Howard Hughes Medical Institute (HHMI) investigator Bruce Lahn at the University of Chicago, reported their findings in an advance access article published on January 13, 2004, in the journal Human Molecular Genetics. Patrick Evans and Jeffrey Anderson in Lahn's laboratory were joint lead authors of the article.

Lahn and his colleagues found that the ASPM gene showed clear evidence of changes accelerated by evolutionary pressure in the lineage leading to humans, and the acceleration is most prominent in recent human evolution after humans parted way from chimpanzees.
“In our work, we have looked at evolution of a large number of genes, and in the vast number of cases, we see only weak signatures of adaptive changes,” said Lahn. “So, I was quite surprised to see that this one gene shows such strong and unambiguous signatures of adaptive evolution — more so than most other genes we've studied.”
By contrast, the researchers' analyses of the ASPM gene in the more primitive monkeys and in cows, sheep, cats, dogs, mice and rats, showed no accelerated evolutionary change. “The fact that we see this accelerated evolution of ASPM specifically in the primate lineage leading to humans, and not in these other mammals, makes a good case that the human lineage is special,” said Lahn.

You might be wondering how exactly scientists can detect selective pressure on a gene. Note how the article talks about mutations that are not functionally significant versus mutations that are functionally significant. Well, compare two related species for the ratio of functionally significant to functionally insignificant variations in the same gene. The higher the ratio the higher the selective pressure must have been.
Here's an intuitive example of why ratios of functionally signficant to functionally insignificant mutations reveal the extent of past selective pressure: Suppose at some point in the past there was a species that has only a million animals of that species. Suppose they had some gene we will call X. Suppose they all had only functionally insignificant mutations in X and that between the million animals of that species they had 20 different combinations of mutations in X. Then suppose a single animal in that species was born that had a mutation in X that caused a functional change that made that animal more adaptive. Perhaps the mutation in X made the animal smarter and therefore more successful in finding food. Well, that animal with the "smart X" variation also had one of the existing 20 combinations of functionally insignificant mutations. The other 19 combinations existed only in animals that did not have the "smart X" intelligence-enhancing mutation. All the other animals of that species will therefore be less successful, on average, at reproducing. That will, over a period of generations, cause those other 19 combinations in the X gene to become far less common. Many of the combinations in X likely will disappear entirely as their carriers become outcompeted in the search for food and fail to reproduce successfully. The 1 combination of insignificant variations that occurs with the "smart X" mutation will become far more common and may become the only combination of insignificant variations in the X gene until new insignificant combinations start accumulating across generations as new mutations happen in animals that have the "smart X" mutation.
The point is that a valuable mutation will mprove the relative reproductive success of the first animal that gets it. But then any unimportant or less important mutations that animal also has will be propagated along with the important mutation. The amount of overall variation in that gene will go down in future generations as the animals that do not have the valuable mutation but which have various functionally insignificant mutations do not reproduce as successfully. Valuable mutations have the effect of reducing the number of functionally unimportant mutational variations that will be found around genes that has the valuable mutations.
Update: Nicholas Wade of the New York Times has more details about the historical frequency of ASPM mutations.
"There has been a sweep every 300,000 to 400,000 years, with the last sweep occurring between 200,000 and 500,000 years ago," Dr. Lahn said, referring to a genetic change so advantageous that it sweeps through a population, endowing everyone with the same improved version of a gene.
By this measure humans may be due for another ASPM mutation. Perhaps there is some human out there walking around with the next intelligence-enhancing ASPM mutation.
Where Lahn talks about a mutation that "sweeps through a population" understand what that really means: All animals that did not have the mutation in a given species were outcompeted and, over some generations, failed to reproduce. The mutation didn't just jump from one ape to another ape like a viral infection. The line of successive mutations were each so helpful for enhancing survival and reproduction that animals that didn't have them were outcompeted for food or for mates or in fights and perhaps in all of those ways.
Wade says at least 5 other genes cause microcephaly but they have not yet been identified. Once they are expect evolutionary geneticists to repeat the same comparison between species as was done with ASPM. While few humans appear to have functional variations in ASPM (aside from victims of microcephaly) it is possible that some of these yet-to-be-discovered genes will turn out to vary between humans. Humans do vary in brain size and brain shape. Genetic variations in some genes must be causing this. Though some of those variations might be occurring in genes that are not responsible for microcephaly.
By Randall Parker at 2004 January 14 12:29 AM Trends, Human Evolution TrackBack