In 1934, an Ontario farmer asked his local newspaper if a birth announcement for five babies born at once would cost the same as a birth announcement for a single baby. A local reporter filed a wire story about the farmer’s suddenly expanded family, and almost overnight, the Dionne quintuplets became media celebrities–to the point where the government took the quintuplets from their parents and exhibited them behind glass at a facility christened Quintland, where, at one point, they drew more tourists than Niagara Falls.
The Dionne Quintuplets were the world’s first surviving quintuplets (that we know of). But they weren’t the last. In fact, now it seems that hardly a year goes by that there isn’t news of quintuplets, sextuplets or even septuplets being born somewhere in the world–most recently, to the McCaughey family of Iowa.
The reason? Fertility treatments. Statistics from the U.S. show the rate of twin births climbed 30 percent from 1980 to 1994, from 18.9 twins per 1,000 births to 24.6, while triplet births rose 200 percent between. In 1994, 315 quadruplets and 46 quintuplets or sextuplets were also born.
Identical twins and “supertwins” (anything more than two) are interesting to scientists because they share the same genes. They originate in a single fertilized egg (a.k.a. a zygote, which is why they’re also called monozygotic). If the zygote splits in two before starting the process of dividing and specializing, the result is identical twins. If one of the cells splits again, the result is more identical offspring.
(Fraternal, or dizyogotic, multiples are different; they occur when two or more eggs are fertilzied and grow to maturity. They share about 50 percent of their genes–the same as any pair of siblings.)
Scientists study identical multiples to try to better understand the relationship between our genetic inheritance and our environment, and how much each contributes to our personalities and abilities.
Some of the similarities are obvious: identical twins look like each other. Some can finish each other’s sentences. (Of course, so can some married couples!) They often have similar talents, and suffer from similar diseases. Even when separated at birth, the paths their lives follow often have many similarities.
Last year, Gerald McClearn of Penn State University and his colleagues reported the results of a major study of twins which gave new insight into how much of the differences in intelligence among different people is due to genetics–55 percent, according to ther study, which included 110 pairs of identical twins and 130 pairs of same-sex fraternal twins, all more than 80 years old.
McClearn studied elderly twins to maximize the effects of environment–80 years worth of it–and also because a major purpose of the study, sponsored by the National Institute of Aging, was to find ways to improve the functioning of older adults. But the study showed that heredity continued to play an important role even after eight decades. In fact, genetic influence seems to increase with maturity: only 20 percent of the variation in infants’ intellectual ability is attributed to genes.
The study actually divided mental ability into three categories, and found that 62 percent of variations in processing speed and 52 percent of memory, but only 32 percent of spatial ability, could be attributed to genes.
Intelligence is one thing; personality is something else. Studies of twins by psychologist Hill Goldsmith show that the genetic influence on personality is much weaker. By watching them play in a lab, he’s able to get a feel for whether they’re aggressive and active, or more passive and easy-going. And he’s finding that environmental variations are very important for differences in personality. Those environmental variations don’t have to be all that great, either; even twins raised together in the same home develop differences in personality because of choosing different friends or activities or suffering from different accidents.
Unfortunately, the home environment isn’t always great for supertwins. Coping with twins is difficult, but fairly manageable; as the number of children increases, however, so do the difficulties. The biggest problem is simply the exhaustion and sleep deprivation suffered by the parents.
That problem can be exacerbated by the dangers of multiple births themselves. Most multiple births are premature, which means the babies are at higher risk of low birthweight, underdevloped lungs, cerebral palsy and other developmental disorders. For every 1,000 births of triplets and higher-order multiples, 167 die in infancy and 179 are disabled–a much higher rate than for twins or singletons. All of these dangers add to the stress the pregnancy and birth place on the parents (and account for the growing concerns over the ethics of fertility treatments that make multiple births more likely).
Other problems include giving enough attention to older siblings and helping them adjust (it’s bad enough when an older sibling suddenly finds himself saddled with a kid brother or sister; imagine Mom coming home with two, three, four or more!), and maintaining a good marital relationship. Some of these problems are common to families, but in a family where a multiple birth has taken place, they’re exponentially greater–and the problems just go on and on, as all the children need braces at the same time, or help with their homework, or college tuition.
According to one Australian study, it takes 198 hours a week to run a household and care for triplets–30 more hours than there are in a week!
Still, there are advantages, too. As the children grow older, they can entertain each other, and the parents don’t have to worry about dealing with kids at various levels of maturity at the same time.
And the children themselves share something with their siblings that those of us who were not part of identical multiple births generally don’t share with ours: an immediate, profound rapport that science can’t really explain. As Louis Keith, an identical twin who directs the Center for the Study of Multiple Birth at Northwestern University, puts it, “You know it’s you–but not you–at the same time.” He figures this feeling is incomprehensible to us singletons.
He’s probably right. But as the number of multiple births rises, it’s a feeling more and more people may share.
