Chapter 1 The Big Picture: Starting Sooner, Lasting Longer The most jaw-dropping fact about modern-day growing up is how much earlier it begins. Today''s kids enter puberty an average of two years younger than their parents did. In fact, it''s not uncommon to hear about kids riding their first wave of hormonal surges three, four, or even five years sooner than the people raising them. The second most stunning fact is how much longer this whole process lasts. Thanks to its mood swings and painfully awkward physical shifts, puberty as a stage of life tends to be equal parts feared and dreaded by parents. At least, reason would dictate, by starting earlier it must progress faster, expediting everyone through this phase. Right? Actually, no. Rather than speeding up, the time line of puberty has stretched like taffy.

One simple example can be found in the average age of a first period: while puberty itself is starting a couple of years sooner than it used to, since the 1940s the age of a first period has barely budged. So today, it is simultaneously true that many kids begin to develop physically well before they ever hit double digits and also that most kids experience hormonally driven changes--from acne to eye rolling--years longer than prior generations. From start to finish, the process can take nearly a full decade. As a result, even though the puberty of the past may not have been kinder or gentler, it was most certainly later and a heck of a lot shorter. The measuring of the pubertal time line is relatively new science. Research looking at "normal" puberty began in earnest in the 1940s, when Dr. James Tanner, a pediatric endocrinologist (aka hormone doctor for kids), launched a study that would span three decades. Starting in 1948, Tanner documented the physical changes of kids living in a postwar orphanage in Harpenden, outside of London.

There are several reasons why this study could never be done today, not the least of which is that Tanner didn''t do any hands-on physical exams but rather studied photographs of each child taken several times per year to examine their pubertal development over time. The growth he tracked was limited to breast or penile and testicular size, depending upon gender, and appearance of pubic hair for all. Tanner then created a numeric scale to classify the progress: stage 1 meant prepubescent with no visible sexual maturation; stage 5 meant fully developed, adult; and stages 2, 3, and 4 fell somewhere in between with certain specific hallmarks. Because Tanner''s staging was so simple and visual, it caught on. And it stuck! This explains why today, 75 years after his study first began, doctors across the world still use Tanner staging to describe progression along the path through physical maturation. Tanner''s scale became particularly helpful as a sort of yardstick for shifting hormones inside the body. Moving from Tanner stage 1--entirely prepubescent--to Tanner stage 2 confirmed that the sex hormones governing these particular body changes were actually present. This, in turn, meant that in the days before certain hormones could be measured in a laboratory, and decades before others had even been discovered, doctors had a way to confirm that sexual maturation was in process.

In addition to staging how kids go through it, Tanner wrote the norms for when they go through it too. His data documenting the adolescence of Baby Boomers showed that the average girl entered puberty just after she turned 11, while the average boy was 11.5 years old. It''s thanks to Tanner''s stages that people are so startled by how early puberty begins these days: if there wasn''t a time expectation, we wouldn''t label it as "early" or "late." Of course, there''s always been a range of pubertal timing--none of us expects to set a clock to these changes. That said, there''s an average age for the onset of puberty and an expected swing on either side, with anything much earlier or later getting noticed. It doesn''t take much to recall the kid in your fifth-grade class who looked like a full-on adult, and another kid in junior year of high school lagging way behind. In puberty parlance, the kids who develop first are called early bloomers and the ones visibly late to the party, late bloomers.

For a long time--certainly before and even long after Tanner''s data was published--there was no agreed-upon definition of what made someone early or late, at least not outside of medical circles. Instead, this was the kind of thing labeled by kids and parents alike, generally not kindly. Tanner examined images of naked kids, but in real, day-to-day life, puberty''s most visible landmarks can even be observed while kids are clothed because the earliest sign for girls is typically a pair of breast buds that seem to poke out of every T-shirt, sweater, and certainly leotard. For boys, though, puberty''s shifts are only publicly obvious a little later on, when some combination of a growth spurt, voice drop, and wispy mustache come into play. Tanner knew that penile and testicular growth were far more accurate measures here, but in a clothed society these go unnoticed and they''re even more subtle because kids tend to move toward privacy just about the same time that their hormones start to surge. So when boys close the door and otherwise keep their clothes on, parents often miss the fact that they''re developing. All of this is why even with robust studies documenting the path through puberty, there has always been lots of room for confusion about who is actually in it, especially among the guys. One potentially misleading indicator: hair.

Ask just about anyone, and they''ll consider pubic hair part of the sexual maturation of puberty. But ask an endocrinologist or a scientist studying this stage of life, and they''ll say something very different: hair might make someone look sexually mature, but it doesn''t make them capable of reproducing. Pubic hair growth is largely governed by hormones released from the adrenal glands sitting on top of the kidneys. These hormones, called adrenal androgens, start to circulate around the same time that estrogen and testosterone are producing the changes of puberty, but don''t be fooled, adrenal androgens are on their own independent path. They might appear at the same time as the hormones ruling puberty, or they might show up much earlier or later. The adrenal androgens stimulate more than just hair follicles--they also tell pores in the skin to secrete sweat and oil, explaining why crops of pubic hair tend to appear along with acne or waves of newly pungent body odor. But none of these downstream impacts signify sexual maturation. Even Tanner didn''t really appreciate the distinction here, which explains why he measured pubic hair as one of his hallmarks of puberty.

It''s confusing that the hormonal pathways through the body don''t always work together, even if things look that way from the outside. Following Tanner''s groundbreaking research, the pipeline of studies of "normal" puberty ran dry. This makes sense, because once a phenomenon has been defined as "normal," it isn''t scientifically sexy to redocument. But in the early 1990s, a nurse practitioner named Marcia Herman-Giddens felt compelled to reexamine Tanner''s assumptions when the patients walking into her office repeatedly defied the expectations he had set: girl after girl appeared to be in Tanner stage 2 well before age 11. Herman-Giddens was quite aware of normal variation, early bloomers and late bloomers, but the trend flowing through her office motivated her to apply for funding to run a fairly large study, ultimately including 17,000 girls. In 1997, she published the results showing that puberty was indeed beginning sooner for genetic females--depending upon ethnicity, anywhere from a year to a year and a half earlier than expected. Herman-Giddens documented a massive shift in puberty and made headlines everywhere.