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Genes in High Places
One relatively speedy example of evolution occurred in Tibet. Tibetans separated from the Han Chinese about 3,000 years ago, moving to a high plateau region. The air at 13,000 feet above sea level has 40 percent less oxygen than at sea level, yet Tibetans do not show typical physical reactions to extreme heights, such as shortness of breath, dizziness, nausea or problems sleeping. These symptoms are caused by excessive red blood cells that work overtime to carry oxygen throughout the body. Chinese biologists discovered that 30 genes changed in order for Tibetans to survive at their elevation. Tibetans are far more likely to have the version of a gene -- an allele -- that produces fewer red blood cells than their Chinese neighbors possess.
The Milky Way
Evolutionary change can result in a lost trait. Early Homo sapiens started to become lactose intolerant as youngsters. This freed up mothers to nurse new siblings. About 8,000 years ago, gene mutations began to appear in the region now known as Turkey. An increasing number of adults were becoming lactose tolerant. In the modern world, lactose intolerance is no longer the norm among adults in Europe, the Middle East, Africa and India. However, worldwide, about 65 percent of adults are still unable to digest milk.
Have a Drink
China is the setting for another evolutionary step. About 10,000 years ago in southern China, alleles that chemically altered alcohol within the body appeared. People with these alleles did not become intoxicated, but their faces flushed. These genetic variations are now common in East Asia. They protect against alcoholism, because individuals with the alleles feel discomfort or sickness after consuming limited amounts of alcoholic drinks. In some areas, up to 90 percent of the population has these alleles. Alcoholics in those regions do not.
Adapting Organisms
Certain insects also seem to be evolving quickly. The heartier bedbugs that sprung up during the late 1990s were more resistant to pesticides and had faster metabolisms than their predecessors. The rootworm, an agricultural pest, adapted to a poison produced by genetically modified corn. An added protein should destroy the digestive track of the insect, but the rootworm is now resistant to the toxin. Some plants are changing, as well. The flowers on South Africa̵7;s Rat̵7;s Tail plant grow at ground level. Birds, who can be pollinators, are not inclined to feed from such a vulnerable spot. The plant has evolved a stalk that makes an ideal aboveground perch.