Lucky 7

Kenneth Robert, the oldest of the McCaughey septuplets born Nov. 19, 1997.
Courtesy of Iowa Health System Affiliates.
As the Iowa septuplets leave their respirators and the headlines, we're reminded that fertility treatments have spawned a wave of multiple births in the United States.
Believe the numbers? The rate of triplet births rose 200 percent between 1980 and 1994. The so-called "supertwins" -- triplets and up -- are becoming almost common. In 1994, 315 quadruplets and 46 quintuplets or sextuplets were also born in the United States.
doll Identical twins and identical supertwins are genetic oddities. Neither carbon copies nor clones, they do have the same genes. And that makes them fascinating to scientists, lay people and themselves. Different and yet the same, some can finish each other's sentences. They often have similar talents -- and diseases. When separated at birth, their life paths often bear an eerie resemblance. And when reunited, they share an immediate, profound rapport that science can't begin to explain.
In short, says Louis Keith, he and his fellow identical twins share unique feelings. "You know it's you -- but not you -- at the same time." Keith, who directs the Center for the Study of Multiple Birth at Northwestern University, figures that this feeling is incomprehensible to anyone without a genetically identical sibling.
doll It's easy to hear echoes of this sentiment on the Web. In Triplet Connection, a web site for supertwins, identical triplet Joan Hensley wrote, "We are so closely bonded. We did everything together. We dressed alike, shared teachers and friends, competed together, shared a bedroom and clothing, and we felt one another's sorrows and joys."
Curious -- and useful
In fact, identical twins are so fascinating that if nature hadn't delivered them, scientists might have had to invent them. Why? Because they help us sort out genetic from environmental influences. Genes, after all, do more than just determine hair color and body height. They affect disease, intelligence and behavior.
Problem is, environment also affects these factors. So if we were curious about how genetics and environment affect a certain disease, we could study people who have identical genes but lived in different environments. If they have the same level and type of disease, then we blame genetics for the illness. Otherwise, we look at the environment.
That typical Why Files oversimplification -- accurate but hideously short of details -- describes some twin studies. Other twin researchers compare the behavior, health or intelligence, and resemblance of identical twins, fraternal twins, and sometimes unrelated individuals.
Skip this if you know "monozygotic" from "dizygotic"

Identical multiples originate in a single fertilized egg, or zygote (that's why they're called monozygotic). If this zygote splits in two before starting its usual process of dividing and specializing, the result is identical twins. If one of the cells separates again, the result is more identical offspring.

Fraternal (dizygotic) multiples originate when two or more eggs are fertilized and grow to maturity. They share, on average, 50 percent of their genes -- just like siblings born separately.

More on smart jeans -- er, genes and smarts.

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The Why Files Staff includes: Terry Devitt, editor; Darrell Schulte, webmaster; Dave Tenenbaum, feature writer; Susan Trebach, team leader.

Kenneth Robert, the oldest of the McCaughey septuplets born Nov. 19, 1997. Courtesy of Iowa Health System Affiliates.	As the Iowa septuplets leave their respirators and the headlines, we're reminded that fertility treatments have spawned a wave of multiple births in the United States. Believe the numbers? The rate of triplet births rose 200 percent between 1980 and 1994. The so-called "supertwins" -- triplets and up -- are becoming almost common. In 1994, 315 quadruplets and 46 quintuplets or sextuplets were also born in the United States. Identical twins and identical supertwins are genetic oddities. Neither carbon copies nor clones, they do have the same genes. And that makes them fascinating to scientists, lay people and themselves. Different and yet the same, some can finish each other's sentences. They often have similar talents -- and diseases. When separated at birth, their life paths often bear an eerie resemblance. And when reunited, they share an immediate, profound rapport that science can't begin to explain. In short, says Louis Keith, he and his fellow identical twins share unique feelings. "You know it's you -- but not you -- at the same time." Keith, who directs the Center for the Study of Multiple Birth at Northwestern University, figures that this feeling is incomprehensible to anyone without a genetically identical sibling. It's easy to hear echoes of this sentiment on the Web. In Triplet Connection, a web site for supertwins, identical triplet Joan Hensley wrote, "We are so closely bonded. We did everything together. We dressed alike, shared teachers and friends, competed together, shared a bedroom and clothing, and we felt one another's sorrows and joys." Curious -- and useful In fact, identical twins are so fascinating that if nature hadn't delivered them, scientists might have had to invent them. Why? Because they help us sort out genetic from environmental influences. Genes, after all, do more than just determine hair color and body height. They affect disease, intelligence and behavior. Problem is, environment also affects these factors. So if we were curious about how genetics and environment affect a certain disease, we could study people who have identical genes but lived in different environments. If they have the same level and type of disease, then we blame genetics for the illness. Otherwise, we look at the environment. That typical Why Files oversimplification -- accurate but hideously short of details -- describes some twin studies. Other twin researchers compare the behavior, health or intelligence, and resemblance of identical twins, fraternal twins, and sometimes unrelated individuals. Skip this if you know "monozygotic" from "dizygotic"
		Identical multiples originate in a single fertilized egg, or zygote (that's why they're called monozygotic). If this zygote splits in two before starting its usual process of dividing and specializing, the result is identical twins. If one of the cells separates again, the result is more identical offspring.
		Fraternal (dizygotic) multiples originate when two or more eggs are fertilized and grow to maturity. They share, on average, 50 percent of their genes -- just like siblings born separately.
	More on smart jeans -- er, genes and smarts.