The Third Twin Page 0,33

of them would have written nothing. Since she had first observed this syndrome, she included as many numbered lists as possible in her lectures.

She was a good teacher - somewhat to her surprise. In general, she felt her people skills were poor. She was impatient, and she could be abrasive, as she had been this morning with Sergeant Delaware. But she was a good communicator, clear and precise, and she enjoyed explaining things. There was nothing better than the kick of seeing enlightenment dawn in a student's face.

"We can express this as an equation," she said, and she turned around and wrote on the board with a stick of chalk:

Vt=Vg+Ve+Vm

"Vt being the total variance, Vg the genetic component, Ve the environmental, and Vm the measurement error." They all wrote down the equation. "The same may be applied to any measurable difference between human beings, from their height and weight to their tendency to believe in God. Can anyone here find fault with this?" No one spoke, so she gave them a clue. "The sum may be greater than the parts. But why?"

One of the young men spoke up. It was usually the men; the women were irritatingly shy. "Because genes and the environment act upon one another to multiply effects?"

"Exactly. Your genes steer you toward certain environmental experiences and away from others. Babies with different temperaments elicit different treatment from their parents. Active toddlers have different experiences than sedentary ones, even in the same house. Daredevil adolescents take more drugs than choirboys in the same town. We must add to the right-hand side of the equation the term Cge, meaning gene-environment covariation." She wrote it on the board then looked at the Swiss Army watch on her wrist. It was five to four. "Any questions?"

For a change it was a woman who spoke up. She was Donna-Marie Dickson, a nurse who had gone back to school in her thirties, bright but shy. She said: "What about the Osmonds?"

The class laughed, and the woman blushed. Jeannie said gently: "Explain what you mean, Donna-Marie. Some of the class may be too young to remember the Osmonds."

"They were a pop group in the seventies, all brothers and sisters. The Osmond family are all musical. But they don't have the same genes, they're not twins. It seems to have been the family environment that made them all musicians. Same with the Jackson Five." The others, who were mostly younger, laughed again, and the woman smiled bashfully and added: "I'm giving away my age here."

"Ms. Dickson makes an important point, and I'm surprised no one else thought of it," Jeannie said. She was not surprised at all, but Donna-Marie needed to have her confidence boosted. "Charismatic and dedicated parents may make all their children conform to a certain ideal, regardless of their genes, just as abusive parents may turn out a whole family of schizophrenics. But these are extreme cases. A malnourished child will be short in stature, even if its parents and grandparents are all tall. An overfed child will be fat even if it has thin ancestors. Nevertheless, every new study tends to show, more conclusively than the last, that it is predominantly the genetic inheritance, rather than the environment or style of upbringing, that determines the nature of the child." She paused. "If there are no more questions, please read Bouchard et al. in Science, 12 October 1990, before next Monday." Jeannie picked up her papers.

They began packing up their books. She hung around for a few moments, to create an opportunity for students too timid to ask questions in open class to approach her privately. Introverts often became great scientists.

It was Donna-Marie who came up to the front. She had a round face and fair curly hair. Jeannie thought she must have been a good nurse, calm and efficient. "I'm so sorry about poor Lisa," Donna-Marie said. "What a terrible thing to happen."

"And the police made it worse," Jeannie said. "The cop who drove her to the hospital was a real asshole, frankly."

"That's too bad. But maybe they'll catch the guy who did it. They're passing out flyers with his picture all over the campus."

"Good!" The picture Donna-Marie was talking about must have been produced by Mish Delaware's computer program. "When I left her this morning she was working on the picture with a detective."

"How's she feeling?'

"Still numb ... but jumpy, too."

Donna-Marie nodded. "They go through phases, I've seen it before. The first phase is denial. They say: 'I just want