An item on yesterday's Science page incorrectly stated that mitochondrial DNA is found in the nucleus of cells. It is in every cell's cytoplasm. (Published 10/26/1999)
Sociality, Morality and the Brain
In 1848, a dynamiting accident drove an iron bar through the skull of a railroad worker named Phineas Gage. Miraculously, Gage survived the accident with no apparent damage to his intellect. His personality, however, changed dramatically. Once a diligent worker, Gage became an irresponsible drifter.
Gage's misfortune provided neuroscientists with what have become landmark insights into how the brain works. The spike damaged Gage's prefrontal cortex, indicating that this part of the brain is critical for social and moral decision-making.
Now, researchers have found new evidence supporting that idea. Antonio Damasio of the University of Iowa and colleagues found two subjects who suffered damage to their prefrontal cortices before the age of 16 months. Both children seemed to recover. But as they aged, the two began to behave aberrantly, stealing, lying, verbally and physically abusing other people, poorly parenting their out-of-wedlock children, showing a distinct lack of remorse, and failing to plan for their futures.
There were no obvious environmental explanations for their behavior--both subjects came from stable, middle-class families and had well-adjusted siblings.
"In conclusion, early dysfunction in certain sectors of prefrontal cortex seems to cause abnormal development of social and moral behavior, independently of social and psychological factors, which do not seem to have played a role in the condition of our subjects," the researchers write in the November issue of Nature Neuroscience. "This suggests that antisocial behavior may depend, at least in part, on the abnormal operation of a multi-component neural system which includes . . . sectors of the prefrontal cortex."
Curing, or Creating, Stress?
One of the reasons many smokers say they enjoy cigarettes is that the habit helps alleviate stress. A new analysis, however, suggests that may not be true.
Andy C. Parrot of the University of East London in Britain reviewed all the scientific evidence about the relationship between smoking and stress and concluded that smoking may simply alleviate the anxiety caused by nicotine withdrawal.
"The regular smoker needs nicotine to maintain normal moods and suffers from unpleasant feelings of irritability and tension between cigarettes, when his or her . . . nicotine levels are falling," Parrot writes in the October issue of American Psychologist. "The majority of smokers recognize that smoking is physically unhealthy, but mistakenly believe it has positive psychological functions."
The DNA Mutations of Aging
Scientists have long suspected that one of the fundamental causes of aging may be the accumulation of damage to a type of DNA located in every cell's nucleus called mitochondrial DNA, which produces energy for cellular functions. Now, researchers have found the first direct evidence supporting this theory.
Yuichi Michikawa of the California Institute of Technology in Pasadena compared the mitrochondrial DNA of people of varying ages and found that certain defects tended to accumulate in those of older people, according to a report in the Oct. 22 issue of Science. More research is needed, the researchers said, to find direct evidence that the mutations play a role in aging.
A Weevil Species' Sexual Ruse
Many creatures have been observed engaging in what appears to be homosexual behavior. Now, a team of researchers has concluded that, at least among one species of beetles, female homosexual behavior is actually a ruse designed to attract the biggest male mates.
Ally R. Harari and colleagues at the University of Florida in Gainesville studied Diaprepes abbreviatus, an inch-long black beetle commonly known as the sugar cane rootstock borer weevil.
Scientists had noticed that females of the species tend to mount other females. When the researchers studied the insects in the laboratory, they found that the sight of a pair of mounted females attracted large males, who are then equally likely to mate with either of the females.
Male beetles appear to rely on sight to identify females, which tend to look very similar to males except for being somewhat larger. By going after mounted pairs, the males are likely to find at least one female to mate with, the researchers conclude.
"In the absence of reliable cues, males search either for larger individuals, as these are more likely to be females, or for mating couples, as one individual is likely to be female," the researchers write in the Oct. 21 issue of Nature.
"Our explanation is consistent with all known cases of naturally occurring female-female mounting in insects, as males have difficulty distinguishing females and so seek females in copulating pairs. By mounting one another, females can increase their opportunities to mate with large males."
CAPTION: Female sugar cane rootstock borer weevils couple; researchers believe the act is aimed at luring males.