Yes, I'm a slow reader. So sue me. (Actually, I've been holding onto this for a couple of days to post it today, knowing that I'll be incommunicado until July 22.) In the meantime, here's another interesting selection from Michio Kaku's latest:
One scientist who has been fascinated ... by the genetics of what makes us "human" is Dr. Katherine Pollard, an expert in a field called "bioinformatics," which barely existed a decade ago. In this field of biology, instead of cutting open animals to understand how they are put together, researchers use the vast power of computers to mathematically analyze the genes in animals' bodies. ...
Dr. Pollard knew that most of our genome is made of "junk DNA" that does not contain any genes and was largely unaffected by evolution. This junk DNA slowly mutates at a known rate (roughly 1 percent of it changes over four million years). Since we differ from the chimps in our DNA by 1.5 percent, this means that we probably separated from the chimpanzees about six million years ago. Hence there is a "molecular clock" in each of our cells. And since evolution accelerates this mutation rate, analyzing where this acceleration took place allows you to tell which genes are driving evolution.
Dr. Pollard reasoned that if she could write a computer program that could find where most of these accelerated changes are located in our genome, she could isolate
precisely the genes that gave birth to Homo sapiens. After months of hard work and debugging, she finally placed her program into the giant computers located at the University of California at Santa Cruz. Anxiously she awaited the results.
When the computer printout finally arrived, it showed what she was looking for: there are 201 regions of our genome showing accelerated change. But the first one on her list caught her attention.
"With my mentor[,] David Haussler[,] leaning over my shoulder, I looked at the top hit, a stretch of 118 bases that together became known as human accelerated region 1 (HAR1)," she recalled.
...
Next she and her colleagues tried to decipher the precise nature of this mysterious cluster called HAR1. They found that HAR1 was remarkably stable across millions of years of evolution. Primates separated from chickens about three hundred million years ago, yet only two base pairs differ between chimps and chickens. So HAR1 was virtually unchanged for several hundred million years, with only two changes, in the letters G and C. Yet in just six million years, HAR1 mutated eighteeen times, representing a huge acceleration in our evolution.
But what was more intriguing was the role HAR1 played in controlling the overall layout of the cerebral cortex, which is famous for its wrinkled appearance. A defect in the HAR1 region causes a disorder called "lissencephaly" or "smooth brain," causing the cortex to fold incorrectly. (Defects in this region are also linked to schizophrenia.) Besides the large size of our cerebral cortex, one of its main characteristics is that it is highly wrinkled and convoluted, vastly increasing its surface area and hence its computational powers. Dr. Pollard's work showed that changing just eighteen letters in our genome was partially responsible for one of the major, defining genetic changes in human history, vastly increasing our intelligence. "Recall that the brain of Carl Friedrich Gauss, one of the greatest mathematicians in history, was preserved after his death and showed unusual wrinkling.)
Dr. Pollard's list went even further and identified a few hundred other areas that also showed accelerated change, some of which were already known. FOX2, for example, is crucial for the development of speech, another key characteristic of humans. (Individuals with a defective FOX2 gene have difficulty making the facial movements necessary for speech.) Another region[,] called HAR2[,] gives our fingers the dexterity required to manipulate delicate tools.
Furthermore, since the genome of the Neanderthal has been sequenced, it is possible to compare our genetic makeup with a species even closer to us than the chimpanzees. (When analyzing the FOX2 gene in Neanderthals, scientists found that we shared the same gene with them. This means that there is a possibility that the Neanderthal could vocalize and create speech, as we do.)
Another crucial gene[,] ... called ASPM, ... is thought to be responsible for the explosive growth of our brain capacity. Some scientists believe that this and other genes may reveal why humans became intelligent but the apes did not. (People with a defective version of the ASPM gene often suffer from microcephaly, a severe form of mental retardation, because they have a tiny skull, about the size of [that of] one of our ancestors, Australopithecus.)
Scientists have tracked the number of mutations within the ASPM gene and found that it has mutated about fifteen times in the last five to six million years, since we separated from the chimpanzee. More recent mutations in these genes seem to be correlated with milestones in our evolution. For example, one mutation occurred over one hundred thousand years ago, when modern humans emerged in Africa, indistinguishable in appearance from us. And the last mutation was 5,800 years ago, which coincides with the introduction of the written language and agriculture.
Because these mutations coincide with periods of rapid growth in intellect, it is tantalizing to speculate that ASPM is among the handful of genes responsible for our increased intelligence. If this is true, then perhaps we can determine whether these genes are still active today, and whether they will continue to shape human evolution into the future.
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