NATURE MEETS NURTURE BEHAVIOR PROBLEMS NOT AS SIMPLE AS XYY, SCIENTISTS ARE LEARNING.

Byline: Evan Henerson Staff Writer

Chalk up your color blindness, athletic coordination or receding hairline to the genetic makeup of your parents and most researchers won't give you an argument. But blame your family tree for alcoholism, schizophrenia or forms of aggressive behavior and, historically, biologists and psychologists have fled to separate corners of the room.

But now, with greater frequency, the two camps are uniting over the conundrum of genetic behavior. Biology plays a role in a person's development, experts say, as does environmental conditioning. How much either factor contributes to - or overrides - the other remains the subject of study and debate.

``Almost all behavior probably has a genetic component,'' says Dr. Juergen Reichardt, associate professor of biochemistry and molecular biology at USC's Keck School of Medicine. ``It may be minor, or it may be major. But if it were all genetic, people would be driving around drunk and killing people, saying, 'My genes made me do it.' That's not particularly helpful.''

Potentially more beneficial - and far in the future, say scientists - is the prospect of identifying harmful and destructive genes and figuring out ways to alter or eliminate them before they manifest themselves. Admittedly, it sounds like something out of a Stanley Kubrick film, but suppose geneticists could ``breed out'' genetic tendencies toward Alzheimer's, obesity or schizophrenia?

A few things we do know about genes: Some traits are carried on the Y chromosome, meaning that they can be passed to male children only. In rare instances, the presence of a single gene can be linked to a given condition. If you have the gene for Huntington's disease, for example, you will get the disease.

When talking about the possible genetic links to behavior, geneticists are more apt to use words like ``tendency'' and bring in environmental factors. Dr. Dean Hamer, chief of the gene structure and regulation section at the National Cancer Institute, has conducted research on subjects ranging from the genetic tendency toward smoking and risk-taking behavior to potential genetic components affecting sexual orientation.

Scientists have focused on the enzyme monoamine oxidase and its effects on the brain. Monkeys and rats with low or nonexistent MAOA levels have demonstrated a greater tendency toward aggressive behavior than their counterparts with normal functioning levels.

The complete absence of MAOA in human beings is extremely rare. A study of a Dutch family published by geneticist Han Brunner in 1993 yielded intriguing results. Among the men in this family - who lacked a gene for producing MAOA - one raped his sister and later, in a mental institution stabbed a warden in the chest with a pitchfork. Another tried to run over his boss with a car, and two others were arsonists.

Complex strands of genes account for most human traits, making the identification of individual behavior genes extremely difficult. And even if they could start influencing behavior in a laboratory, scientists caution that an entirely new set of ethical issues would crop up.

``You'd still be making a leap of faith each time along the way,'' says Dr. Kenneth Goldberg, assistant professor of psychology at Widener University in Pennsylvania. ``Who are we to say that just because you have a particular genetic code you're going to get a certain condition?''

``And at what point are psychologists willing to draw the barrier?'' continues Goldberg. ``We might be comfortable intervening with something like Alzheimer's, because we know that's bad, but not aggression. Maybe we wouldn't have any more aggressive football players.''

Already the XYY defense, a theory that linked the presence of an extra male chromosome to criminal behavior, is largely a thing of the past, says Dr. David Comings, director of medical genetics at City of Hope National Medical Center in Duarte, who is frequently recruited to testify in court cases about an individual's biological tendencies.

``At times it helps a little bit, but it never gets them off,'' says Comings, who noted that the defense attorneys for convicted serial killer Richard Speck couldn't make an XYY defense fly. ``It's been determined that the extra Y chromosome has a fairly minor effect on behavior. I think when they found that a lot of university professors had an extra Y, they determined it wasn't such a bad thing.''

By now, retired Long Beach, N.Y., police detective Vincent LaMarca has heard quite enough about gene behavior, including a theory - debunked by most scientists - that he might be the carrier of a ``murder gene.''

LaMarca's father, Angelo, was a convicted kidnapper and murderer. More than 40 years later, Vincent son's, Joey, was jailed for the murder of a drug dealer. Yet LaMarca dismisses attempts to blame his chemistry for the actions of his family.

``In this society, we all seem to have a need to place blame on something outside, rather than taking responsibility for what we did,'' says LaMarca, whose story inspired the recent film ``City by the Sea.''

``My son was bitter and angry and influenced by drugs. Yeah, he said (he inherited a murder gene), and I think he's sorry he ever said it.''

Scientists believe that the study of genetic behavior still has a place in the laboratory as well as in field studies. Several years after earning a doctorate in molecular biology, Dr. Susan Carswell - a student of Goldberg's at Widener - switched her focus to psychology. The focus of her second Ph.D: aggressive behavior.

While research into the genetic components of behavior is taking place, Carswell maintains the field is relatively sparse largely because the two academic disciplines didn't exactly speak the same language.

``I was aware from day one of entering this program that most psychologists were not attuned to the biological underpinnings of what we were studying, while most biologists were similarly uninformed about the psychological realities of their findings,'' says Carswell. ``The two bodies of research were almost completely separated.''

The gap appears to be closing. A team of genetic and psychological researchers led by Dr. Avshalom Caspi recently published an article in Science magazine examining the link between children and violent behavior. The study identified the presence of the mutated MAOA but concluded that even those with the mutation weren't necessarily more likely to become violent criminals.

``What this says is that two things were required in order to end up having genetics affect aggressive behavior,'' says Carswell. ``You need a genetic predisposition and environmental factors. Abused kids with the normal gene were not aggressive, while kids with the altered gene were not aggressive unless they had been abused.''

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(1 -- cover -- color) in the genes?

Scientists explore whether aggressive tendencies are inherited or learned

(2) Vincent LaMarca