[music playing]

Narrator: The sun's shining, the birds are singing, and it's Karen White's favorite part of the day. Time for a cup of coffee, and a chat with her neighbor and best friend.

Karen White: Do you want to come around? I've got that [inaudible] video.

Lynn White: All right then. Only if you've got coffee and biscuits.

Karen White: Shall we say five minutes?

Lynn White: All right then.

Narrator: Lynn is Karen's identical twin. They've been inseparable since they were born. They went to the same schools, have always lived in the same town, and on occasion, had the same boyfriend.

Karen White: We went out on New Year's Eve. And I ended up kissing Mark on the stroke of midnight. And I didn't like the way he kisses, so I bit his tongue— or his lip, I think— and said, oh! And Lynn ended up marrying him.

Lynn White: Of course, after New Year's Eve, when he got back to where— don't know why— the funny thing is, I started talking to him. So he thought that it was me that he had kissed. And he thought, ooh she's had the change of heart, or whatever, and he's just started being friendly. And then he realized that it was Karen he had kissed, but it was me that he actually wanted to go out with, isn't it? So it was really strange.

Narrator: As well as sometimes fancying the same blokes, they have the same taste in clothes, and have the same sense of humor.

Tv Actor 1: Oh, I'll never shoot myself.

Tv Actor 2: I know, shame.

[laughter]

Narrator: As identical twins, Karen and Lynn have exactly the same set of genes. They're clones. And they've also had the same upbringing. The question is, how much their personality traits are determined by their genes. The view was that genes played little, if any, role in shaping our personalities. How could something as complex as the human psyche be explained away by few strands of DNA? Well it turns out, that it can.

This DNA analysis is painting a new, and astonishing picture of the role that genes play in influencing our behavior.

Man 1: It's almost unbelievable the results, because they suggest that genetics is important almost across the board. You can find some traits, surprisingly like shyness for example, that show somewhat more genetic influence than other traits, for example, femininity. But the more striking thing is that no one has demonstrated any personality trait to show no genetic influence.

[music playing]

Narrator: Psychological studies of twins raised apart have shown that behavior such as addiction and criminality have a genetic basis. But these have been debunked, partly because many top scientists don't take psychology seriously. But also, some say, because of political correctness. To even hint that people are born bad, or born clever, could be seen as running counter to a century of social reform. But in the coming years, our comfortable views of human nature may have to be changed.

Woman: The Human Genome Project has been completed in terms of sequencing the human genome. And there's going to be a lot of research over the next few years in trying to understand what those different kind of genes do. And some of those genes, of course, will not be involved in disease-related conditions. They'll be involved in human characteristics, in which we all have some kind of experience, whether it's sort of with fear or anxiety, sexual orientation. And so I think there'll be a lot of interest from the public, and from media, in this kind of research as it unfolds. And we need to think about how that research is going to be applied, and whether the results should be applied.

Narrator: One of those research programs is into depression. Norma, her sister Margaret, and niece, Vanessa, have all suffered.

Norma: For me, it feels as if I am cut off from the rest of the world. It's like having a glass shield in front of you. You can see what's going on, but you're not part of it. It just built up to the feeling I just couldn't go on anymore. And I took a few days off, and that few days has gone into ten years.

[murmuring]

Narrator: Their parents and children have also suffered. In all, 10 members of their family have been affected. Genes are obviously a factor.

Researcher: Does the depression feel worse at any particular times of day?

Norma: First thing in the morning.

Narrator: Researchers from the Institute of Psychiatry are trying to track down some of the genes involved. They scour the country looking for suitable families. They first diagnose a condition, and later samples of the patient's blood are sent off for analysis.

Vanessa: If it was something that was found to be a genetic problem, it would just make it a lot easier to deal with. Perhaps the blame would go away.

Narrator: The women's DNA is stored in a freezer, along with samples from other depressed people. Computers can now rapidly read the genetic code of each patient, and compare it with that of non-depressed people. If there's a difference between the two, then genes are probably involved. These men of the world's foremost scientists in behavioral genetics. As well as studying depression, they're homing in on genes influencing intelligence, addiction, and even anti-social behavior.

Man 2: You're thinking that even these sorts of differences are real.

Narrator: And if the research all comes off, it could help to identify those likely to develop problems when they're children, and then take preventive steps.

Man 3: It does raise the question as to whether anti-social behavior should be regarded like depression or schizophrenia— as a disease— and there are those who believe that it should. But, in a sense, I suppose the main issue is whether it has a partly biological basis, and as I said, I think there is evidence that it does. So the real question is, in the long term, would one be able to use genetic evidence to, for example, make medication that alters anti-social behavior? And again, that's a possibility.

Man 1: And if you could intervene before the problems become problems, I think it's likely to be much more effective, even from a cost point of view, but especially from the child's life. You don't wait for problems to happen before you do anything about them. Because we aren't that good at dealing with problems once they're full blown.

Narrator: Mick McDade wishes someone had spotted his problem early. He used to be an alcoholic, but he's fine now, and able to visit a fun fare with his doctor, David Ball, who's trying to track down the genes that help drive Mick to drink.

DR. DAVID BALL: If we can find the genes involved, then we can understand the biology of what's going on when people are rather vulnerable to becoming alcohol dependent, or what happens when they become alcohol dependent. Now if we can understand the biology, then we can develop better treatments to work on that biology. It may also be possible, on the basis of a genetic test, to identify those individuals which may respond to that particular form of treatment, or may respond to a different form of treatment, which may even be psychological.

Narrator: Dr. Ball thinks the same set of genes are involved in other types of addiction. He and other researchers suspect that some people are driven to drink or drugs because of a chemical imbalance in their brain that can only be compensated by intense stimulation.

[screaming]

And controversially, they believe that ordinary thrill seekers, like these, are driven to search out excitement and adventure because of their genes.