A Slate special issue on the science, history and culture of multiple births.

The first children born of in vitro fertilization are almost 30 years old. In their lifetimes, and due in part to the technology that enabled their births, we've seen a minor revolution in family structure. Since 1980, the incidence of twinning has increased by more than 70 percent: What once seemed an oddity has grown ever more commonplace. Whether this twin boom is the product of fertility treatments or something else, twins (or triplets or quads) now figure into thorny issues of family planning. Once they were considered a miraculous gift. Now we talk about whether it's OK to reduce a pregnancy by design.

A new generation of kids, overpopulated with same-aged siblings, has changed the landscape of playgrounds, classrooms, and nurseries. Even the material culture of childhood has been upsized and iterated to sustain the waves of multiples. And our cultural obsession with twins has only redoubled: In the 1980s we gawked at the Pisner quintuplets; in the aughts we turned to the Octomom.

The science of twins, meanwhile, has flourished in its own way. Sibling pairs now swab their cheeks and send off their living detritus for a DNA scan, to find out, once and for all, if they're genetically alike. Scientists use vast databases of information on twins to sort nature from nurture, and assert—rightly or not—the heritability of complex behaviors. Other researchers study "twin speak," looking for insight into the nature of language.

Twins may not be so special anymore, and that's why they're worth thinking about.

"Double Take: There are four new shows about identical twins," by Troy Patterson.  Posted Aug. 25, 2011.

"Dorothy Burlingham's Twins: The study that explained why it's not so wonderful to have a look-alike," by David Greenberg and Maida Greenberg. Posted Aug. 24, 2011.

"O Brother, What Art Thou? Russ is my identical twin. At least that's what we've always said …," by Barry Harbaugh. Posted Aug. 24, 2011.

"Double Inanity: Twin studies are pretty much useless," by Brian Palmer. Posted Aug. 23, 2011.

"Dugon, Haus You Dinikin, Du-Ah: The secrets of twin speak," by Jon Lackman. Posted Aug. 23, 2011.

"Are Twins Taking Over? Making sense of the dramatic rise in multiple births," by Angela Tchou. Posted Aug. 23, 2011.