Is the Human Brain Still Evolving? Some Scientists Think So
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This is SCIENCE IN THE NEWS in VOA Special English. I'm Bob Doughty. And I'm Faith Lapidus. On our program this week -- new thinking about the brain ...
Good news for coffee drinkers ...
And the secret of water-climbing insects.
Two studies suggest that the human brain continues to change through the process of evolution. The findings conflict with a common belief that the brain has evolved about as much as it ever will. Scientists say modern humans developed about two hundred thousand years ago.
Bruce Lahn of the Howard Hughes Medical Institute and the University of Chicago led the studies. The findings appeared in Science magazine.
Scientists looked at changes in two genes related to the size of the brain. These two genes do not work right in people with microcephaly. Microcephaly is a rare condition in which people are born with a brain that is much smaller than normal. Some scientists believe this is what the brain of early humans might have looked like.
In the new studies, the scientists looked at different versions of the two genes. They studied genetic material from people of different ethnic groups. They found that one version of each gene appeared again and again.
The scientists say the changes appear to have spread because they improved the brain in some way. They say the new versions are so common, they cannot be considered an accident.
Instead, the scientists suggest there was pressure to spread through natural selection. Natural selection is a process in which genetic changes that are helpful to a species survive and spread quickly.
The scientists found that the new versions of the two genes evolved much faster in apes than in mice and rats. They decided that these changes might have had an important part in human evolution. The scientists studied how often the changes appeared in the genes of many different populations.
They found that a version of the gene called Microcephalin formed only about thirty-seven thousand years ago. This version appears today in about seventy percent of humans. The scientists say it is more common outside of southern Africa.
The second gene is called ASPM. The studies showed that a version of this gene developed just about six thousand years ago. Today it is found in about thirty percent of all people. It is more common in people from Europe and areas including North Africa, the Middle East and South Asia.
Different populations make use of different genetic changes. Genes must react to the pressures of many environments and threats such as disease.
The scientists who did the studies now want to see if the two genes only act on brain size or also perform other duties. They point out that the genetic changes took place around the same time as important cultural changes. These include the development of things like art and religion and, more recently, civilizations.
Scientists do not know, however, if the two genes are connected to intelligence or problem-solving abilities. Such questions about the mind produce debate. Some scientists are concerned that the new findings might be used to claim that not all groups are created equal.
Some insects can climb what seem like walls of water without moving their legs. They might do this to leave their eggs on land or to avoid attackers. Now, researchers in the United States have found how the insects are able to use this special skill.
John Bush and David Hu are mathematicians at the Massachusetts Institute of Technology in Cambridge. Mr. Bush is a professor; Mr. Hu is a graduate student. For the past four years, they have been studying how small insects travel on the surface of lakes and other areas of water.
The two men used a video camera to make high-speed images of three kinds of insects. Nature magazine reported the results of their study.
They describe how the insects are able to climb areas where the water meets land or another surface, such as a plant. Such areas are called menisci [meh-NIH-sky].
Menisci are common in the environment. They can even be found in a glass of water, where the edge of the water rises to meet the side of the glass.
Mr. Hu says most people do not recognize them because menisci are only a few millimeters high. But to small insects, he says, they are like mountains.
The two men found that the insects were unable to climb menisci with their usual movements. The insects climbed halfway up after a running start, but then slid back down. So the insects changed their body position to create forces that helped to pull them up.
Two kinds of water treaders have claws at the end of their legs that can pull back, or retract. This helps the insects hold onto the surface of the water and pull it up and out of shape. As a result, the insects are able to ride on small areas in the water that can support their body weight.
Professor Bush says the insects produce extremely small menisci with their front and back legs. One meniscus creates a pulling force on another. The combined effect with the meniscus of the water pulls the insect up and over the edge of the surface.
Another insect deals with the problem another way. The larva of the waterlily leaf beetle forms a rounded shape with its back. This action creates menisci at each end, and produces the same effect as with the other insects.
The two researchers also found that the insects climbed up menisci at speeds of up to thirty body lengths a second. The fastest human runners can move about five body lengths a second.
Scientists are finding that coffee does more than help you stay awake. Researchers in the American state of Pennsylvania say coffee has high levels of antioxidants. Antioxidants have been shown to help prevent cancer, heart disease and other conditions.
Joe Vinson is a chemistry professor at the University of Scranton. He says Americans get more antioxidants from coffee than any other food or drink. He reported the findings at a recent meeting of the American Chemical Society.
The body produces chemical substances that cause oxidation. Atoms and molecules called free radicals are involved. Oxidation damages cells and tissues. Experts say this damage causes many of the health problems common in older people.
Antioxidants reduce or prevent oxidation. In recent years, other studies have shown the health value of drinking red wine and tea. Both are known to be high in antioxidants.
Professor Vinson said he and his team compared the antioxidant levels of more than one hundred different foods. They examined everything from fruits and vegetables to oils and popular drinks.
Next, the team compared its findings with information from the United States Department of Agriculture. This information showed what Americans eat and drink and in what amounts. The researchers found that coffee won in both comparisons.
Americans drink large amounts of coffee. And, coffee rated among the very best in antioxidants. One kind of fruit, the date, is actually higher in antioxidants in each serving. However, in the United States, drinking coffee is more popular than eating dates.
Professor Vinson warned that having a diet high in antioxidants is not always a good idea. This is because the body cannot always use these compounds. Scientists do not yet fully understand how the body takes in and uses the substances.
Also, too much caffeine may cause nervousness and other problems.
Professor Vinson said that one to two servings of coffee a day is fine. He also suggested that people eat more fruits and vegetables. They contain not only antioxidants but also high levels of substances such as minerals and fiber.
SCIENCE IN THE NEWS was written by Katherine Gypson, George Grow and Dana Demange. Cynthia Kirk was our producer. I'm Faith Lapidus. And I'm Bob Doughty. Our programs are online at voaspecialenglish.com. To send us e-mail, write to [email protected] Join us again next week for more news about science in Special English on the Voice of America.