Cloning adds a dimension to nature-nurture debate Identical humans are not in the cards

March 09, 1997|By Jonathan Bor | Jonathan Bor,SUN STAFF

Identical genes do not make identical people.

That's important to remember, according to leading scientists, in the wake of a Scottish researcher's announcement two weeks ago that he had successfully cloned an adult sheep and named it Dolly.

The report instantly kindled fears and fantasies about the possibility -- perhaps the inevitability -- that a human will someday be cloned.

But while clones might bear an uncanny resemblance to their genetic forebears, researchers say that the experience of growing up in a different place and time would ensure identities of their own.

Even now, identical twins growing up under the same roof can turn out differently.

Dr. Victor A. McKusick, a Johns Hopkins researcher who is considered the father of medical genetics, ought to know. He is an identical twin, having split 75 years ago from an embryo that also produced his brother, Vincent L. McKusick.

"I am well aware of the differences, even though my twin and I have precisely the same genomes," said McKusick, who has spent 50 years deciphering the impact of inheritance.

The Scottish scientist, Dr. Ian Wilmut, arrives in Baltimore today for a conference that is modestly called "Impact of Molecular Biology on Animal Health and Production Research." The meeting will be held tomorrow and Tuesday at the Hyatt Regency Hotel.

Nature, nurture and chance

How much variation would exist between clone and cloned remains a matter of conjecture -- a mental exercise that builds upon years of debate over the competing roles played by nature and nurture.

Increasingly, brain researchers are talking also about the role played by chance.

Personality, they say, is shaped not only by genes and environment but also by random connections that are made during fetal development as nerve cells organize themselves into the complex computer that is the brain.

Dr. Larry J. Siever, director of outpatient psychiatry at Mount Sinai Hospital in New York, said clones would be no more alike than identical twins -- probably less so.

While twins share the same fetal environment and usually the same household, a clone modeled from an adult would develop in a different womb and grow up in a different environment altogether.

'Mystical concepts'

"People have mystical concepts about clones, like they are the same person, but nobody really believes identical twins are the same person," said Siever, author of "The New View of the Self," a book about the impact of genes on personality.

Clones, and twins, are like houses built from the same blueprints.

"They are painted differently, landscaped differently. You'd walk into one instead of the other and realize you are in the wrong place," Siever said.

"But they do come from the same map, and there's a lot alike."

For example, Victor McKusick and his brother are slender, stand 6 feet, one-half inch tall and are easily mistaken for each other if not seen together.

Victor McKusick describes his brother as the more argumentative one who veered toward a legal career, eventually becoming chief judge of the Supreme Court of Maine.

Victor McKusick might have become a physician even if a random event hadn't exposed him at age 15 to the fascinations of medicine.

Nonetheless, he traces his career to the weeks he spent in Massachusetts General Hospital, recovering from a serious illness.

"My twin escaped that, and as a result of my illness, I saw a great deal of medicine," he said. "My interest got bent in that direction."

Personality more mutable

Physical characteristics, said McKusick, are less mutable than elements of personality.

Genes carry the code for height, hair, eye color and skin pigmentation, and there is little the environment can do to change that.

They can also determine one's chances of getting a disease such as Huntington's, cystic fibrosis and muscular dystrophy.

Mental illness also tends to run in families, but with less consistency.

Schizophrenia, for instance, has a strong genetic component.

But the disease is duplicated in identical twins about half the time -- if one twin has it, the other has a 40 percent to 60 percent chance of developing it, too.

"There may be differences in the brain between the affected twin and the unaffected," said Siever.

"Possibly, environment also comes into play."

For years, scientists have studied identical twins for clues to the relative importance of genes and environment.

Researchers have found support for the contention that environment is -- and isn't -- significant.

Some of the most famous work has been done by Dr. Thomas J. Bouchard and Auke Tellegen, researchers at the University of Min- Clones9A

Pub Date: 3/09/97

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