Natural Limitation to Evolutionary Processes (2/14/05)

Genetic resistance to AIDS works in different ways and appears in different ethnic groups. The most powerful form of resistance, caused by a genetic defect, is limited to people with European or Central Asian heritage. An estimated 1 percent of people descended from Northern Europeans are virtually immune to AIDS infection, with Swedes the most likely to be protected.All those with the highest level of HIV immunity share a pair of mutated genes -- one in each chromosome -- that prevent their immune cells from developing a "receptor" that lets the AIDS virus break in. If the so-called CCR5 receptor -- which scientists say is akin to a lock -- isn't there, the virus can't break into the cell and take it over.To be protected, people must inherit the genes from both parents; those who inherit a mutated gene from just one parent will end up with greater resistance against HIV than other people, but they won't be immune. An estimated 10 percent to 15 percent of those descended from Northern Europeans have the lesser protection.Using formulas that estimate how long genetic mutations have been around, researchers have discovered that the mutation dates to the Middle Ages. (Similar research in mitochondrial DNA -- passed along by women -- has suggested that Europeans are all descended from seven Ice Age matriarchs.)Why would the mutation stick around so long instead of giving up the ghost? Researchers initially thought the mutation provided protection against the bubonic plague that caused the Black Death in Europe. Those with the mutation would have lived longer and had more children while many of their neighbors died off. The fact that the genetic mutation also provided protection against HIV centuries later would just be a coincidence.The plague scenario has been largely discarded in favor of another deadly scourge. "A disease like smallpox that has been continuous since that time ... is more likely," said Yale University professor of epidemiology Alison Galvani, who co-wrote a study about the possible smallpox link in 2003.According to Galvani, while the plague came and went, smallpox stuck around well into the 20th century, providing even more incentive for a protective gene to live on: It would keep people alive generation after generation, instead of just during one brief epidemic.

Well, what if a mutation caused the destruction of a disease-causing gene?Would you consider that to be detrimental and negative?And I also think you are harboring another misconception about what happens in this particular mutation.This mutation is is a change in the nuceotide sequence. No genes have been lost (although that can happen, just as additions can also happen). I just have a different nucleotide sequence in that particular gene than someone who has all of their wisdom teeth.