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FROM BACH TO BEDOUINS, IN SEARCH OF CLUES TO HOW PUBERTY BEGINS:
An eighteenth-century choir // A gene that “kisses” // Harry Potter // Saudi cousins // Songbirds //And, of course, pimply faced adolescents.

Adolescent Development: The Turning Point

By Stephen S. Hall // Fall 2006
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Puberty

D. Corson/ClassicStock

For 27 years, until his death in 1750, Johann Sebastian Bach led three male choirs in Leipzig. Most of the singers were teenagers, almost all of them musical prodigies. By the standards of the time, German school officials kept excellent records on each student, including his date of birth, academic performance and family history. More than two centuries later, an enterprising historian had the idea of poring over those records in an attempt to document, retrospectively, an adolescent trait that is very pertinent to the male choir business.

One of the classic physiological changes of puberty—indeed, one of the most gratingly obvious—is when a boy’s voice “cracks,” or deepens. In the late 1960s, S. F. Daw, a researcher at Worcester College in Oxford, England, attempted to correlate the change in voice, and thus the timing of puberty in eighteenth-century boys, with the part each of Bach’s choristers sang. (Music historians believe that boys whose voices had not yet broken sang soprano, the highest vocal part for male adolescents; boys in the midst of changing sang alto; and boys in whom the change was complete sang tenor and bass.) The results, which Daw published in 1970 in the journal Human Biology, suggested that the average age of a boy whose voice was changing was about 16.5 to 17 years—some three years later than the comparative age for a modern European boy.

Many of the changes in physical features during puberty, such as height and shape and sexual maturation, are obvious, but less visible aspects of development also occur throughout the adolescent body. A voice breaks, for example, because of a growth spurt in the larynx, which stretches out the size of the vocal cords and, like loosening the strings on a guitar, lowers the voice.

The cycle of change generally unfolds during a three-year period, although the starting gun for these enormous transformations goes off at different times for different children. For some puberty starts early; for others, insufferably late. What’s more, the timing has significant—and, scientists think, lifelong—ramifications for the psychological makeup and well-being of adults, affecting everything from self-esteem to such unhealthy behaviors as substance abuse. But that shouldn’t be surprising, really, when one considers that some of the most profound changes occur in the adolescent brain.

Scientists have been studying puberty (the word derives from the Latin pubescere, “to grow hairy”) in humans for decades, but until recently, there was still a central mystery: Boys and girls are suspended in childhood until the brain registers some unknown combination of environmental cues and genetic prompts, unleashing a cerebral signal—for puberty really begins in the head. All the tumultuous shudders of physical change in the armpits, bones and groin begin when a small nub of neural tissue known as the hypothalamus emits a barely perceptible chemical whisper. But what flips the switch to initiate puberty? What tells the brain that it is time to change a sexually immature child into a reproductively competent adult?

In the 1970s, two scientists, one at the Salk Institute in San Diego (Roger Guillemin), the other at Tulane University in New Orleans (Andrew Schally), competed to discover the hormone that controls sexual development in humans. When the dust settled, both had a hand on the prize: a molecule known as gonadotropin-releasing hormone, usually abbreviated GnRH.

The discovery reshaped the working biochemical definition of puberty. “Everyone thought the pituitary was the master gland,” remembers William F. Crowley Jr., who began practicing endocrinology just after Schally and Guillemin did their pioneering work. “It turns out that the pituitary, like all of us, works for someone else. The real boss is the hypothalamus.”

The new, biochemical description of puberty goes like this: The hypothalamus releases tiny squirts of GnRH, sending a chemical message that travels just two or three millimeters—the length of a hyphen—to the pituitary gland, which, in turn, begins releasing small, pulsed secretions of two hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Those hormones act on the sexual organs of both boys (testicles) and girls (ovaries), causing them gradually to grow in size and to release more, increasingly potent, sex-specific hormones—estradiol in girls and testosterone in boys.

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Ready or Not

Kisspeptin, named after a sweet chocolate treat, jumpstarts puberty. But when does the gene that produces it know when to start?

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hed-dossier

1.The GPR54 Gene as a Regulator of Puberty,” by Stephanie B. Seminara, Sophie Messager, Emmanouella E. Chatzidaki, Rosemary R. Thresher et al., New England Journal of Medicine, Oct. 23, 2003. An account of experiments that showed that a defect in the gene prevents puberty in mice and humans, thus revealing the gene’s pivotal role.

2.The Adolescent Brain: A Work in Progress,” by Daniel R. Weinberger, Brita Elvevåg and Jay N. Giedd, June 2005 [The National Campaign to Prevent Teen Pregnancy]. A highly readable exploration of how the teenage brain undergoes refining and restructuring.

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