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The Science Of Adolescence

Mighty_Emperor

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And you thought it was just spots and fits of picque ;)

Teenagers special: The original rebels

* 05 March 2005
* From New Scientist Print Edition. Subscribe and get 4 free issues.
* Lynn Dicks
* Lynn Dicks is a writer based near Cambridge, UK


EAST Africa, one-and-a-half million years ago: a group of women sit with their young children. They are heavy-browed with small skulls - not quite human, but almost. Some are checking their children for ticks, others teaching them how to dig tubers out of the ground. Not far off, a gaggle of teenage girls lounge under a tree, sniggering and pointing at some young men who are staging fights nearby. The older women beckon: "Come and help us dig out this root - it will make a great meal," they seem to say. But the girls reply with grunts and slouch off, sulkily.

Could this really have happened? Our immediate ancestors, Homo erectus, may not have had large brains, high culture or even language, but could they have boasted the original teenage rebels? That question has been hotly contested in the past few years, with some anthropologists claiming to have found evidence of an adolescent phase in fossil hominids, and others seeing signs of a more ape-like pattern of development, with no adolescent growth spurt at all. This is not merely an academic debate. Humans today are the only animals on Earth to have a teenage phase, yet we have very little idea why. Establishing exactly when adolescence first evolved and finding out what sorts of changes in our bodies and lifestyles it was associated with could help us understand its purpose.

We humans take twice as long to grow up as our nearest relatives, the great apes. Instead of developing gradually from birth to adulthood, our growth rate slows dramatically over the first three years of life, and we grow just a few centimetres a year for the next eight years or so. Then suddenly, at puberty, growth accelerates again to as much as 12 centimetres a year. Over the following three years adolescents grow an astonishing 15 per cent in both height and width. Though the teenage years are most commonly defined by raging hormones, the development of secondary sexual characteristics and attitude problems, what is unique in humans is this sudden and rapid increase in body size following a long period of very slow growth. No other primate has a skeletal growth spurt like this so late in life. Why do we?

Until recently, the dominant explanation was that physical growth is delayed by our need to grow large brains and to learn all the complex behaviour patterns associated with humanity - speaking, social interaction and so on. While such behaviour is still developing, humans cannot easily fend for themselves, so it is best to stay small and look youthful. That way you do not eat too much, and your parents and other members of the social group are motivated to continue looking after you. What's more, studies of mammals show a strong relationship between brain size and the rate of development, with larger-brained animals taking longer to reach adulthood. Humans are at the far end of this spectrum.

If this theory is correct, the earliest hominids, Australopithecus, with their ape-sized brains, should have grown up quickly, with no adolescent phase. So should H. erectus, whose brain, though twice the size of that of Australopithecus at around 850 cubic centimetres, was still relatively small. The great leap in brain capacity comes only with the evolution of our own species and Neanderthals, starting almost 200,000 years ago. Brains expanded to around 1350 cm3 in our direct ancestors and 1600 cm3 in Neanderthals. So if the development of large brains accounts for the teenage growth spurt, the origin of adolescence should be here. The trouble is, some of the fossil evidence seems to tell a different story.

“If Homo erectus did go through a teenage phase, that scuppers the idea linking late growth with development of a big brain”

The human fossil record is extremely sparse, and the number of fossilised children minuscule. Nevertheless in the past few years anthropologists have begun to look at what can be learned of the lives of our ancestors from these youngsters. One of the most studied is the famous Turkana boy, an almost complete skeleton of H. erectus from 1.6 million years ago found in Kenya in 1984. The surprise discovery is that there are some indications that he was a young teenager when he died.

Accurately assessing how old someone is from their skeleton is a tricky business. Even with a modern human, you can only make a rough estimate based on the developmental stage of teeth and bones and the skeleton's general size. For example, most people gain their first permanent set of molars at age 6 and the second at 12, but the variation is huge. Certain other features of the skull also develop chronologically, although the changes that occur in humans are not necessarily found in other hominids. In the middle teenage years, after the adolescent growth spurt, the long bones of the limbs cease to grow because the areas of cartilage at their ends, where growth has been taking place, turn into rigid bone. This change can easily be seen on an X-ray.

You need as many of these developmental markers as possible to get an estimate of age. The Turkana boy did not have his adult canines, which normally erupt before the second set of molars, so his teeth make him 10 or 11 years old. The features of his skeleton put him at 13, but he was as tall as a modern 15-year-old. "By human standards, he was very tall for his dental age," says anthropologist Holly Smith from the University of Michigan at Ann Arbor. But you get a much more consistent picture if you look at Turkana boy in the context of chimpanzee patterns of growth and development. Then, his dental age, bone age and height all agree he was 7 or 8 years old. To Smith, this implies that the growth of H. erectus was primitive and the adolescent growth spurt had not yet evolved.

Susan Anton of New York University disagrees. She points to research by Margaret Clegg, now at the University of Southampton in the UK, showing that even in modern humans the various age markers often do not match up. Clegg studied a collection of 18th and 19th-century skeletons of known ages from a churchyard in east London. When she tried to age the skeletons blind, she found the disparity between skeletal and dental age was often as great as that of the Turkana boy. One 10-year-old boy, for example, had a dental age of 9, the skeleton of a 6-year-old but was tall enough to be 11. "The Turkana kid still has a rounded skull, and needs a lot of growth to reach the adult shape," Anton adds. Like apes, the face and skull of H. erectus changed shape significantly between youth and adulthood. Anton thinks that H. erectus had already developed modern human patterns of growth, with a late, if not quite so extreme, adolescent spurt. She believes Turkana boy was just about to enter it.

If she's right, and small-brained H. erectus went through a teenage phase, that scuppers the orthodox idea linking late growth with development of a large brain. Anthropologist Steven Leigh from the University of Illinois at Urbana-Champaign is among those who are happy to move on. He believes the idea of adolescence as catch-up growth is naive; it does not explain why the growth rate increases so dramatically. He points out that many primates have growth spurts in particular body regions that are associated with reaching maturity, and this makes sense because by timing the short but crucial spells of maturation to coincide with the seasons when food is plentiful, they minimise the risk of being without adequate food supplies while growing. What makes humans unique is that the whole skeleton is involved. For Leigh, this is the key. Coordinated widespread growth, he says, is about reaching the right proportions to walk long distances efficiently. "It's an adaptation for bipedalism," he says.

According to Leigh's theory, adolescence evolved as an integral part of efficient upright locomotion, as well as to accommodate more complex brains. Fossil evidence suggests that our ancestors took their first steps on two legs as long as six million years ago. If proficient walking was important for survival, perhaps the teenage growth spurt has very ancient origins. Leigh will not be drawn, arguing that there are too few remains of young hominids to draw definite conclusions. While many anthropologists will consider Leigh's theory a step too far, he is not the only one with new ideas about the evolution of teenagers.

A very different theory has been put forward by Barry Bogin from the University of Michigan-Dearborn. He believes adolescence in our species is precisely timed to improve the success of the first reproductive effort. In girls, notes Bogin, full adult shape and features are achieved several years before they reach full fertility at around the age of 18. "The time between looking fertile and being fertile allows women to practise social, sexual and cultural activities associated with adulthood, with a low risk of having their own children," says Bogin. When they finally do have children, they are better prepared to look after them. "As a result, firstborns of human mothers die much less often than firstborns of any other species."

In boys, you see the opposite. They start producing viable sperm at 13 or 14 years of age, when they still look like boys. The final increase in muscle size that turns them into men does not happen until 17 or 18. In the interim boys, who feel like men, can practise male rivalries without being a threat to adult men or an attractive option to adult women. When boys do become sexually active, they have practised and are more likely to be successful without getting hurt.

Bogin's theory makes totally different predictions to Leigh's. If the timing of adolescence is related to uniquely human cultural practices, our species should be the first and only one to have a teenage phase. "H. erectus definitely did not have an adolescence," he asserts. Such strong and opposing views make it all the more necessary to scour the fossil record for clues.

One approach, which has produced a surprising result, relies on the minute analysis of tooth growth. Every nine days or so the growing teeth of both apes and humans acquire ridges on their enamel surface. These perikymata are like rings in a tree trunk: the number of them tells you how long the crown of a tooth took to form. Across mammals, the speed of tooth development is closely related to how fast the brain grows, the age you mature and the age you die. Teeth are good indicators of life history because their growth is less related to the environment and nutrition than is the growth of the skeleton. Slower tooth growth is an indication that the whole of life history was slowing down, including age at maturity.

Back in the 1980s Christopher Dean, an anatomist at University College London, was the first to measure tooth growth in fossils using perikymata. He found that australopithecines dating from between 3 and 4 million years ago had tooth crowns that formed quickly. Like apes, their first molars erupted at 4 years old and the full set of teeth were in place by 12. Over the years, Dean's team has collected enough teeth to show that H. erectus also had faster tooth growth than modern man, but not so fast as earlier hominids. "Things had moved on a bit," he says. "They had their full set of teeth by about 15." Modern humans reach this stage by about age 20. The change in H. erectus seems to imply that the growth pattern of modern humans was beginning to develop, with an extended childhood and possibly an adolescent growth spurt. Dean cautions, though, that the link between dental and skeletal development in ancestral hominids remains uncertain.

These findings could equally support Leigh's or Bogin's theories. A more decisive piece of evidence came last year, when researchers in France and Spain published their findings from an analysis of Neanderthal teeth. A previous study of a remarkably well-preserved skeleton of a Neanderthal youth, known as Le Moustier 1, from south-west France had suggested that, with a dental age of 15 and the frame of an 11-year-old, the kid was about to undergo an adolescent growth spurt. But the analysis of his perikymata reveals quite a different picture. Rather than continuing the trend towards slower development seen in H. erectus, Neanderthals had returned to much faster tooth growth (Nature, vol 428, p 936) and hence, possibly, a shorter childhood.

“Bogin believes that adolescence is precisely timed to improve the success of the first reproductive effort”

Does this mean they didn't have an adolescence? Lead researcher Fernando Ramirez-Rozzi, of the French National Centre for Scientific Research (CNRS) in Paris thinks Neanderthals died young - about 25 years old—primarily because of the cold, harsh conditions they had to endure in glacial Europe. Under pressure from this high mortality, they evolved to grow up quicker than their immediate ancestors. "They probably reached maturity at about 15," he says, "but it could have been even younger." They would have matured too fast to accommodate an adolescent burst of growth. He points to research showing that populations of Atlantic cod have genetically changed to mature more quickly under the intense fishing pressure of the 1980s. Others contest Ramirez-Rozzi's position. "You can't assume, just because Neanderthals' teeth grew faster, that their entire body developed faster," says Jennifer Thompson of the University of Nevada, Las Vegas, one of the researchers involved in the Le Moustier 1 study.

Controversy rages, but these latest findings at least highlight one aspect of adolescence that most scientists can agree on. Whatever the immediate purpose of the late growth spurt, it was made possible by an increase in life expectancy. And that being so, one way to work out when the first teenagers originated is to look at the lifespan of a species. This is exactly what Rachel Caspari of the University of Michigan at Ann Arbor has been doing. Her most recent study, published in July 2004, shows an astonishing increase in longevity that separates modern Homo sapiens from all other hominids, including Neanderthals (Proceedings of the National Academy of Sciences, vol 101, p 10895). She categorised adult fossils as old or young by assessing whether they had as much wear on their last molar, or wisdom tooth, as on other molars. "In modern humans we see a massive increase in the number of people surviving to be grandparents," she says. The watershed comes as recently as 30,000 years ago.

On this evidence, Neanderthals and H. erectus probably had to reach adulthood quickly, without delaying for an adolescent growth spurt. So it looks as though Bogin is correct — we are the original teenagers. Whether he is right about the purpose of adolescence is another matter. He admits we will never know for sure. "Fossils will never give us growth curves," he says, "and we should not expect our ancestors to grow like we do."

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From issue 2489 of New Scientist magazine, 05 March 2005, page 39

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It's not just the hormones ...

Scientists are discovering the real reasons for the hell of adolescence, writes Vivienne Parry

Thursday March 3, 2005
The Guardian

Something very strange happens at puberty, when truckloads of hormones begin arriving by the day. Children who were once sweet, helpful and good fun to be around turn, almost overnight, into grunting creatures, who wear nothing but black, lie abed until noon and consume 5,000-calorie snacks (followed immediately by saying that they are still hungry).

They are spotty, frequently smelly, and grow out of every item of clothing they have in the space of a few months. Their boredom threshold plummets and they do not seem able to concentrate on anything for more than five minutes at a time. You begin to wonder whether your child is a changeling, swapped with your own by an alien from the Planet MTV while you weren't looking.

Teenagers are trapped in limbo, neither children nor adults. An excruciating mix of vulnerability and potential, which by turns engages, inspires and alienates adults - everything they do has a high intensity feel about it. We know this because our own adolescent experiences - our first kiss, the first time we fell in love, the first time we drove a car alone - still burn brightly 30 or 40 years on.

There is a darker side, too - soaring rates of serious accident, illicit use of drugs or alcohol, risky sexual behaviours and their consequences and the first signs of emotional disorders which may be lifelong. Teenagers seem to be the very embodiment of hormonal mayhem - or are they? The truth about teenagers and hormones is not what you expect.

Puberty is an extraordinary hormonal event and humans are lucky in that they only have to go through it once -not the norm in the rest of the animal kingdom. Most animals do not become sexually active, and then remain so as we do, but go through the trauma of multiple hormone onslaught every new breeding season.

Human puberty is also unusual, because unlike all other animals, there is a gap between the time reproductive hormones first appear and the prime reproductive age. Boys become fertile at around 13, whilst they are still puny and unappealing. Girls on the other hand, acquire a womanly shape at puberty yet are relatively infertile for several years thereafter. It's not as far out of sync as it appears; the conjunction of top male specimen at around 20 and fully reproductive female at 18, is reflected in the average age of first birth across all cultures of 19 years of age.

The first hormone event which will lead to puberty is largely hidden from us. Between the ages of six and eight, the adrenal glands on top of each kidney start to step up secretion of androgens such as DHEA (dehydroepiandrosterone), which the body uses as construction material for the manufacture of other steroids. These androgens prime hair follicles for pubic hair growth and make the skin greasier. Body odour is also a key feature. Parents first notice this change at their children's parties, when 20 rampaging seven-year-olds are noticeably whiffy in a way that they were not when younger.

The next big change involves the reproductive hormones. The hypothalamus, a part of the brain located roughly behind the eyes, is the grand vizier of the hormone system in the body and is connected by a stalk to the pituitary gland, which dangles beneath it. In adult men, and in women of reproductive age, it is its constant pulses of gonadotrophin-releasing hormone (GnRH) that tell the pituitary to secrete its hormones, which then act on ovary and testes to produce eggs and sperm, and also the hormones oestrogen and testosterone. These have a profound influence on behaviour as well as body shape, turning a child into a sexual adult. During childhood, there is no production of GnRH, almost as if a brake had been applied. Only when that brake is released - and no one is quite sure what the signal for this is - does puberty start.

In boys, luteinizing hormone (LH) from the pituitary stimulates production of testosterone by cells in the testes. Simultaneously, levels of the substances that keep testosterone under lock and key in the bloodstream (sex hormone binding globulins) decrease, thus making even more testosterone available - in total, up to 50 times more than was experienced before puberty. That is some hormone rush.

Once oestrogens and testosterone begin to appear, it is their impact on body form which provides the most dramatic expression of adolescence. Oestrogen stimulates growth of the womb and breast but also determines the shape of the female figure by re-arranging the deposition of fat. In boys the consequence of testosterone is also to sculpt the body, increasing lean body mass and shaping features as well as to promote body hair and beard growth.

Teenagers get a rush from intensity, excitement and arousal. Loud music, big dippers, horror movies? That's where you'll find teenagers. In some teens this thrill-seeking and quest for novelty is subtle and easily managed. In others, the reaction is more severe and can become out of control. This is reflected in the statistics for teenager deaths, three quarters of which result from accident or misadventure.

It is tempting - indeed it has always been assumed - that such behaviours are entirely hormone-driven. After all, aren't teenagers hormones on wheels? From all that I have said so far, it seems logical. But links between hormone levels and poor behaviour in teenagers are either weak, or non-existent.

Nevertheless, if the number one risk factor for homicide is maleness (as it is) and the second is youth, and given that boys have loads of testosterone, and girls don't (or certainly not nearly as much), surely this must put testosterone in the dock as the cause of aggressive adolescent behaviour?

Actually not. First, there is no consistent relationship between normal circulating testosterone levels and violence in teenagers. In fact, there is a rather better correlation between high testosterone levels and levels of popularity and respect from peers. One hypothesis is that teenage boys pick up cues from the environment and use them to determine "normal" behaviour. This is illustrated by recent work from the MRC unit at the Institute of Psychiatry which shows that it is not testosterone levels that determine your waywardness as a teenager, but basically, the people you hang with. Keep the company of bad boys, and you will take your behaviour cue from them. Hang out with sober sorts and your behaviour will be like theirs. As we all remember, being split up from your best mate is a peril of adolescence. "They're a bad influence on you" is the general gist of parental or teacher wisdom on this one. Oh dear. The ignominy of the Institute of Psychiatry proving Miss Mansergh, year nine form teacher, right.

Deprivation may be a more important determinant of teenage violence. The theory - and there is a wealth of literature on this subject - is that if low-status males are to avoid the road to genetic nothingness (the words of neuroscientist Steven Pinker), they may have to adopt aggressive, high-risk strategies. If you've got nothing, you have nothing to lose through your behaviour. Certainly, in humans, both violence and risk-taking behaviour show a pronounced social gradient, being least in the highest social classes and most in the lowest ones. This is surely not what you would expect if testosterone were the only driver of violence.

Another clue that testosterone is not the whole story here is that teenage girls, while not as violent, certainly rival boys for downright bloody-mindedness during their adolescent years. Worse, I can hear some parents say.

The thing that is really irritating about teenagers (and by now you will have guessed that I have two teenage boys) is that one moment their behaviour is that of adults, while the next it is that of a not very bright three-year-old, or possibly, a retarded chimpanzee. Or an amoeba. The rapid oscillation between child and adult is one of the hallmarks of the teenager.

In fact teenage brains are going through a process of maturation, and it is this maturation which many now believe to be responsible for much of the behaviour that we classically attribute to hormones. These changes are independent of hormones and are a function of age.

It has only been discovered very recently that there are two main features of brain maturation that happen to coincide with puberty. Previously it was believed that the brain was pretty well set by adolescence but only in the last couple of years, and to everyone's surprise, it has been realised that maturation is not completed until late teens or even early 20s. One feature is that myelin, a sort of fatty insulating material, is added to axons, the main transmission lines of the nervous system, which has the effect of speeding up messages. The other feature is a pruning of nerve connections, the synapses, in the pre-frontal cortex. This is an area of the brain which is responsible for what is called executive action, which is a shopping list of the things that teenagers lack - such as goal-setting, priority-setting, planning, organisation and impulse-inhibition. During childhood, for reasons that are not clear, a tangle of nerve cells sprout in this brain area, which lies behind the eyes, but during puberty, these areas of increased synaptic density are then reduced by about half, presumably to increase efficiency.

These changes in the adolescent brain that occur around the time of puberty primarily affect motivation and emotion, which manifest themselves as mood swings, conflict with authority and risk taking. This new information has altered thinking about the effect of hormones on teenagers, because it has been realised that what we would call typical adolescent behaviour is not actually the result of hormones alone. For example, it is not just testosterone that drives risk taking, but the inability of the immature brain to assess risk properly that gets them into trouble.

This has particular implications for sexual behaviour. Female adolescents have, thanks to their hormones, the body shape of a woman. In male adolescents, testosterone is driving them to think of sex every six seconds (as little as that?). Meanwhile, their reasoning is temporarily disabled while their brain sets up the "under reconstruction" sign. It's a recipe for disaster.

The remodelling of the cortex helps explain another feature of teenagers: their astonishing level of self-centredeness. For a while, as their brain is undergoing changes, they find it hard to recognise other's emotions. If you show teenagers pictures of faces, they will be some 20% less accurate in gauging the emotions depicted, not recovering this ability until they are 18 or so. This may be one of the reasons why they seem unable to read the signs, when treading on thin ice with their behaviour, with no appreciation of the impact of what they are doing on those around them. Teenagers exist in a universe of one.

Is there any hormone link to high-risk choices in teenagers? It is likely not to be testosterone, at least not initially, but the stress hormone, cortisol which returns us to deprivation. Stress during early life raises cortisol levels, so increasing behavioural problems (such as hyperactivity), tending to make children more aggressive, less affiliative and more likely to perceive others as threatening. Stress in either pregnancy or in early life permanently resets the stress response of the child, so that there is an increased reaction to stress - it's called hyperarousal. A stressed child, for instance, when meeting someone new (even in a familiar environment) will withdraw and refuse to make eye contact, rather than chat happily. This increased stress response plays out in reduced life expectancies because cortisol affects almost every body system. It is also closely linked with depressive illness in later life.

So testosterone plays a part here only after the fact. Aggression and stress raise testosterone levels. Aggression and stress also reinforce each other at the biological level. Animal work reported in the journal Behavioural Neuroscience recently suggests that there is a fast feedback loop between stress hormones and the hypothalamus, which allows aggressive behaviour to escalate.

Another example of how hormones play only a minor role in the drama of adolescent life is to do with sleep. As every parent knows, teenagers find it very hard to get out of bed in the morning and to go to bed at night. Compare and contrast with what they were like as five-year-olds, when you had trouble keeping them in bed beyond six in the morning. Actually, this isn't just your teenagers being difficult, for a subtle biological shift in sleep patterns occurs during puberty, probably to ensure more sleep during rapid growth. There is an increase in the level of the hormone melatonin, which is the slave of the body clock, released during hours of darkness and intimately involved with sleep patterns. The effect of this change is similar to that of shifting the hapless teen through several time zones on a transatlantic flight, resulting in their classic school holiday sleeping pattern of 2am until noon.

Come term-time, the teenage body is in disarray as it is forced by a 7am wake up call - while still on Planet MTV time - to gather itself together, even though it thinks it's four in the morning. These jetlagged teenagers have come around by the end of the week to Parental Time Zone hours, only to wreck themselves with another bout of 2am to noon sleeping at the weekend. Many become chronically sleep-deprived, with all the implications for behaviour that implies - irritability, inability to concentrate, poor attention span - which is inevitably reflected in their school performance.

For all their maddening traits, teenagers are still glorious creatures. Full of promise and potential. The truth about hormones may help us understand them a little better.

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Teenage myths, so hard to beat

Fried food gives you spots

Acne is common in both sexes during adolescence. Mums tell their teens that their spots are the result of eating too much chocolate or fatty food. Not enough fresh air (as in, you've been in your room too long) is also proffered as a cause. Actually, it is the fault of your hormones, not your diet. There is an abnormal response in the skin to normal levels of testosterone in the blood. This has a profound effect on appearance for some unlucky people. The response is self-limiting and goes away with time, but there is no way of predicting how long it will take - it can be a couple of years or decades.

You won't grow up to be a six-footer if you don't sleep at night

Adolescence is marked by a huge surge in growth hormone production. The secretion of growth hormone is carefully timetabled in a pattern that persists through puberty. Growth hormone is released principally at night during sleep, short bursts, every one to two hours during the deep sleep phase. So when your mum says "if you don't go to bed now, you won't grow up to be big and strong," she's right. If onset of sleep is delayed, so is onset of growth hormone release. Children who are deprived of sleep are smaller than they should be.

The surge of GH follows that of increasing levels of GnRH. The relationship between these two hormones is not a direct one, however, but an indirect one, involving oestrogen. The idea that a female hormone is driving growth in boys as well as girls, is counterintuitive at first, but it explains much about the gender differences in growth. Before the onset of the teenage growth spurt, boys grow very slightly faster than girls, but a girl's growth spurt starts about two years before that of boys between 12 and 14. For some four years, girls are, on average, taller than boys. But by adulthood, men are on average 14cm taller than women. This difference is almost entirely due to what happens at puberty - for boys grow on average for two years longer after puberty. It also helps explain why girls grow earlier and faster than boys - it's because they have oestrogens which pump up the production of growth hormone.

The age of puberty is falling

The age of puberty (or rather first period) was 17 in the mid 19th century and is now about 12. This is largely due to better nutrition: a hormone produced by fat, leptin, seems to permit puberty in girls when body fat reaches a certain percentage of body weight. It is probably not the trigger for puberty. The sedentary nature of many children may also have contributed to a lowering in puberty age. Hower, after many decades of fall, it seems to have stabilised, and indeed, some European countries, including the UK, have seen a modest rise in the age of girls at their first period.

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· Taken from The Truth About Hormones by Vivienne Parry (Atlantic Books, March 21). To buy for £9.99 including free p&p call Guardian book service on 0870 836 0875 or go to guardian.co.uk/bookshop. © Vivienne Parry 2005

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Noooooo!! That's so, like, unfair!!! I hate you!!! :furious:
 
Coppertop said:
Noooooo!! That's so, like, unfair!!! I hate you!!! :furious:

turn that racket off now! :D
 
If what they say is true, then it meens Im still in my teens...

<goes off to sulk in room>
 
One and a half million years ago?


Surely Everyone knows Teenagers weren't discovered til the late 1950s.
 
No, they found evidence of all night drinking parties and drumkits back in the last Ice age
 
When boys do become sexually active, they have practised and are more likely to be successful without getting hurt.

What sort of courtin' do they do in those parts? :shock:

One of the most worrying things about teenagers is that they are all indestructible.

They will never get pregnant, catch a disease, crash the car, get caught drink-driving or die. The fact that other teenagers do serves only to show that this one won't, cos it 'appened to 'im dinnit, not me! :roll:

So it's no use offering teenagers Horrible Examples. They have no empathy.
 
Thats NOT music, it's just bloody noise! We had to make do just with the rocks, didn't have roll... wheel not invented y'see.
 
Are teenage brains too 'immature' for right/wrong decisions

Bad Brains
How the Supreme Court's teen execution decision proves too much
Ronald Bailey

Last month the Supreme Court ruled that teenagers under age 18 who commit premeditated murder cannot be executed. The court based its ruling in part on recent studies that found that the frontal lobes of teenagers were not sufficiently developed, making them not fully responsible for their actions. To justify its ruling, the court majority adopted many of the arguments put forth in an amicus brief sponsored by the American Medical Association and the American Psychiatric Association, among others.

That brief argued that recent neuroimaging studies had found that the "brain's frontal lobes are still structurally immature well into late adolescence. The prefrontal cortex (which.is most associated with impulse control, risk assessment, and moral reasoning) is 'one of the last brain regions to mature.'" Consequently, the amicus brief concluded the evidence "based upon studies of normal adolescents, leads to the conclusion that normal adolescents cannot be expected to operate with the level of maturity, judgment, risk aversion, or impulse control of an adult. Adolescents cannot be expected to transcend their own psychological or biological capacities. However, an adolescent who has suffered brain trauma, a dysfunctional family life, violence, or abuse cannot be presumed to operate even at standard levels for adolescents."

Naturally, death penalty opponents and child advocacy organizations hailed the court's decision. But this diminished capacity argument could well play out in disturbing ways.

Already the immature teen brain argument has been used by legislators to impose various restrictions on teenage drivers, including limits on times they can drive, the number of passengers they can carry, and their use of mobile phones. That may appear reasonable; after all, teenagers do account disproportionately for traffic accidents.

Progressives who applauded the Supreme Court's decision with regard to imposing the death penalty might not be so happy when conservatives turn around and use that decision to justify imposing more parental consent laws on teenage women who are seeking an abortion. And will statutory rape laws need to be revised in light of the findings with regard to the immaturity of teenage brains? Furthermore, if teenagers aren't responsible for their actions with regard to violence, driving, or sex, how can they be expected to cast their ballots responsibly in elections? For that matter, how can teenagers responsibly sign up for military service? And surely the immaturity defense can be used by the tens of thousands of juveniles who are arrested each year for drug abuse offenses.

But let's set aside teenage brains for the moment. What about the brains of adults? A new study from Australia has found that parts of the frontal lobes of drug addicts are underdeveloped. "We believe that this braking system is faulty in patients with compulsive behaviours like addiction, such that affected individuals cannot stop themselves even though they know the consequences of their actions could be devastating," says Murat Yucel, who led the research.

Violent adult criminals also seem to have brain abnormalities that might fall under the Supreme Court's teen murderer decision. Brain researchers at the University of Southern California (USC) imaged the brains of 21 men with psychopathic personalities who had committed serious violent crimes. They found that they had "an 11 percent to 14 percent reduction in the volume of nerve cells in the prefrontal cortex compared to normal males—a deficit of about two teaspoons' worth." Tellingly, Adrian Raine, the USC psychopathologist who headed up the study, noted that the prefrontal cortex appears to be critical for self-restraint and deliberate foresight. "One thing we know about antisocials is that they do not think ahead," said Raine.

So the question naturally arises: If teenage culpability for criminal behavior (and other behaviors, for that matter) is reduced on the grounds that their brains do not function like normal adult brains, shouldn't the culpability of adults whose prefrontal cortexes are similarly underdeveloped be reduced? Should adults with stunted frontal lobes "be expected to transcend their own psychological or biological capacities?"

In any case, what would it mean to "transcend" one's psychological or biological capacities? We're all limited by our psychological and biological capacities. As neuroscience advances and we become better able to peer inside our skulls, we may find that many of us—possibly most of us—have exculpatory neuronal glitches. If a person hits someone else, wouldn't that mean, by definition, that the executive faculties in his frontal lobes had failed to exercise their inhibitory functions? His neurons made him do it; but they are his neurons, and he's responsible for them.

University of California–San Diego neurophilosopher Patricia Churchland points out that a child learns about proper moral behavior in the social world the same way he or she learns about the physical world—that is, by interacting with it himself or watching others. The child then either bears the consequences of his actions or sees the consequences of other people's choices. Churchland concludes, "The default presumption that agents are responsible for their actions is empirically necessary to an agent's learning, both emotionally and cognitively, how to evaluate the consequences of certain events and the price of taking risks."

The Supreme Court's underage execution decision has us slipping far down the slope of universal neurological exculpation, and it raises interesting questions about what standard we should use to hold people responsible in criminal cases. I would suggest an old-fashioned one: If a person can distinguish between right and wrong, then we hold her responsible for her actions. Interestingly, the AMA's amicus brief noted, "Cognitive experts have shown that the difference between teenage and adult behavior is not a function of the adolescent's inability to distinguish right from wrong."

The legal system is part of the social machinery aimed at training our neurons to behave properly. Neuroscience may inform our judgments about whether our neurons have been properly trained, but in the end we have no choice but to hold people responsible for their actions. After all, it's not as though the young murderer in the case the Supreme Court considered got off scot-free. He's likely to be imprisoned for the rest of his life. In this case, one hopes that both teenagers and the rest of us learn impulse control by watching bad things happen to those who don't succeed in controlling their impulses.


Ronald Bailey is Reason's science correspondent. His new book, Liberation Biology: A Moral and Scientific Defense of the Biotech Revolution will be published in June by Prometheus Books.

Source: reason.com/rb/rb032305.shtml
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One of the things I've learned in the psychology components of my course is that teenagers' brains do not compute in the same way as do Earthlings'.

They may have few powers of foresight and little idea of the possible implications of their own actions, eg when driving too fast or engaging in risky sex.

This is, I have been taught, purely physiological and is usually a passing phase. My personal and professional experience of teenagers tends to back this up.

(My experience includes the care and detention of deeply troubled teenagers including murderers.)
 
It's not only physical development of the teenage brain. When you're young things like risk of death, disease or even the future just doesn't occur to you - they seem 'far off'. Same goes for 'young adults' who have a reasonable income and think nothing of blowing vast quantities of cash in t'pub each night and who scoff at things like pensions, savings etc.

I should know - I break into mournful sobs when I remember the money I've spent in my heady youth on utterly trivial and ultimately transitory things, like beer, fags and ... er ... beer. In effect we pay in later years double for what we spent in our youth.

Summing up, I think it's not only a physiological development that means teenagers have a different sense of responsibility - it's also a perceptual problem as well as a 'life' experience problem. An older person might've seen more of the results of short-sighted risk consideration.
 
Why teens do bizarre things

Vivienne Parry The Guardian

Scientists are discovering that it’s not just the hormones that cause the turbulence of adolescence. Brain maturation that continues till the teenager is 20 years old is more likely the cause .

Something very strange happens at puberty, when truckloads of hormones begin arriving by the day. Children who were once sweet, helpful and good fun to be around turn, almost overnight, into grunting creatures, who wear nothing but black, lie abed until noon and consume 5,000-calorie snacks (followed immediately by saying that they are still hungry).

Their boredom threshold plummets and they do not seem able to concentrate on anything for more than five minutes at a time. You begin to wonder whether your child is a changeling, swapped with your own by an alien from the Planet MTV while you weren't looking.

There is a darker side, too — soaring rates of serious accident, illicit use of drugs or alcohol, risky sexual behaviours and their consequences and the first signs of emotional disorders which may be lifelong. Teenagers seem to be the very embodiment of hormonal mayhem — or are they? The truth about teenagers and hormones is not what you expect.

Teenagers get a rush from intensity, excitement and arousal. Loud music, big dippers, horror movies? That's where you'll find teenagers.

It is tempting — indeed it has always been assumed — that such behaviours are entirely hormone-driven. After all, aren't teenagers hormones on wheels? It seems logical. But links between hormone levels and poor behaviour in teenagers are either weak, or non-existent.

Learning from peers

First, there is no consistent relationship between normal circulating testosterone levels and violence in teenagers. In fact, there is a rather better correlation between high testosterone levels and levels of popularity and respect from peers. One hypothesis is that teenage boys pick up cues from the environment and use them to determine "normal" behaviour.

This is illustrated by recent work from the MRC unit at the Institute of Psychiatry which shows that it is not testosterone levels that determine your waywardness as a teenager, but basically, the people you hang with.

Keep the company of bad boys, and you will take your behaviour cue from them. Hang out with sober sorts and your behaviour will be like theirs. As we all remember, being split up from your best mate is a peril of adolescence.

Deprivation may be a more important determinant of teenage violence. In humans, both violence and risk-taking behaviour show a pronounced social gradient, being least in the highest social classes and most in the lowest ones. This is surely not what you would expect if testosterone were the only driver of violence.

Another clue that testosterone is not the whole story here is that teenage girls, while not as violent, certainly rival boys for downright bloody-mindedness during their adolescent years. Worse, I can hear some parents say. The rapid oscillation between child and adult is one of the hallmarks of the teenager.

The teenage brain

In fact teenage brains are going through a process of maturation, and it is this maturation which many now believe to be responsible for much of the behaviour that we classically attribute to hormones.

It has only been discovered very recently that there are two main features of brain maturation that happen to coincide with puberty.

Previously it was believed that the brain was pretty well set by adolescence but only in the last couple of years, and to everyone's surprise, it has been realised that maturation is not completed until late teens or even early 20s.

One feature is that myelin, a sort of fatty insulating material, is added to axons, the main transmission lines of the nervous system, which has the effect of speeding up messages. The other feature is a pruning of nerve connections, the synapses, in the pre-frontal cortex. This is an area of the brain which is responsible for what is called executive action, which is a shopping list of the things that teenagers lack — such as goal-setting, priority-setting, planning, organisation and impulse-inhibition.

During childhood, for reasons that are not clear, a tangle of nerve cells sprout in this brain area, which lies behind the eyes, but during puberty, these areas of increased synaptic density are then reduced by about half, presumably to increase efficiency.

These changes in the adolescent brain that occur around the time of puberty primarily affect motivation and emotion, which manifest themselves as mood swings, conflict with authority and risk taking. This new information has altered thinking about the effect of hormones on teenagers, because it has been realised that what we would call typical adolescent behaviour is not actually the result of hormones alone. For example, it is not just testosterone that drives risk taking, but the inability of the immature brain to assess risk properly that gets them into trouble.

Sexuality in teenagers

This has particular implications for sexual behaviour. Female adolescents have, thanks to their hormones, the body shape of a woman. In male adolescents, testosterone is driving them to think of sex every six seconds (as little as that?). Meanwhile, their reasoning is temporarily disabled while their brain sets up the "under reconstruction" sign. It's a recipe for disaster.

The remodelling of the cortex helps explain another feature of teenagers: their astonishing level of self-centredeness. For a while, as their brain is undergoing changes, they find it hard to recognise other's emotions. If you show teenagers pictures of faces, they will be some 20% less accurate in gauging the emotions depicted, not recovering this ability until they are 18 or so. This may be one of the reasons why they seem unable to read the signs, when treading on thin ice with their behaviour, with no appreciation of the impact of what they are doing on those around them. Teenagers exist in a universe of one.

Effects of stress

Is there any hormone link to high-risk choices in teenagers? It is likely not to be testosterone, at least not initially, but the stress hormone, cortisol which returns us to deprivation.

Stress during early life raises cortisol levels, so increasing behavioural problems (such as hyperactivity), tending to make children more aggressive, less affiliative and more likely to perceive others as threatening.

Stress in either pregnancy or in early life permanently resets the stress response of the child, so that there is an increased reaction to stress — it's called hyperarousal. A stressed child, for instance, when meeting someone new (even in a familiar environment) will withdraw and refuse to make eye contact, rather than chat happily. This increased stress response plays out in reduced life expectancies because cortisol affects almost every body system. It is also closely linked with depressive illness in later life.

So testosterone plays a part here only after the fact. Aggression and stress raise testosterone levels. Aggression and stress also reinforce each other at the biological level.

Another example of how hormones play only a minor role in the drama of adolescent life is to do with sleep. As every parent knows, teenagers find it very hard to get out of bed in the morning and to go to bed at night. Compare and contrast with what they were like as five-year-olds, when you had trouble keeping them in bed beyond six in the morning.

Actually, this isn't just your teenagers being difficult, for a subtle biological shift in sleep patterns occurs during puberty, probably to ensure more sleep during rapid growth. There is an increase in the level of the hormone melatonin, which is the slave of the body clock, released during hours of darkness and intimately involved with sleep patterns.

The effect of this change is similar to that of shifting the hapless teen through several time zones on a transatlantic flight, resulting in their classic school holiday sleeping pattern of 2am until noon.

Come term-time, the teenage body is in disarray as it is forced by a 7am wake up call — while still on Planet MTV time — to gather itself together, even though it thinks it's four in the morning.

These jetlagged teenagers have come around by the end of the week to Parental Time Zone hours, only to wreck themselves with another bout of 2am to noon sleeping at the weekend. Many become chronically sleep-deprived, with all the implications for behaviour that implies - irritability, inability to concentrate, poor attention span — which is inevitably reflected in their school performance.

For all their maddening traits, teenagers are still glorious creatures. Full of promise and potential. The truth about hormones may help us understand them a little better.

Source
 
Scientists are discovering that it’s not just the hormones that cause the turbulence of adolescence. Brain maturation that continues till the teenager is 20 years old is more likely the cause .
So raise the voting age back to 21, like it were when I were a lad!

No wonder we get crap governments, with loads of morons eligible to vote! :evil:
 
rynner said:
Scientists are discovering that it’s not just the hormones that cause the turbulence of adolescence. Brain maturation that continues till the teenager is 20 years old is more likely the cause .
So raise the voting age back to 21, like it were when I were a lad!

No wonder we get crap governments, with loads of morons eligible to vote! :evil:

And 21 to take a driving test too.
 
This recent study suggests the exploratory and risky behavior patterns of adolescence aren't limited to humans, and they're important for configuring the adult brain.
A lack of self control during adolescence is not uniquely human

Impulsiveness in adolescence isn't just a phase, it's biology. And despite all the social factors that define our teen years, the human brain and the brains of other primates go through very similar changes, particularly in the areas that affect self-control. Two researchers review the adolescent brain across species on August 20 in the journal Trends in Neurosciences.

"As is widely known, adolescence is a time of heightened impulsivity and sensation seeking, leading to questionable choices. However, this behavioral tendency is based on an adaptive neurobiological process that is crucial for molding the brain based on gaining new experiences," says Beatriz Luna of the University of Pittsburgh, who co-authored the review with Christos Constantinidis of Wake Forest School of Medicine.

Structural, functional, and neurophysiological comparisons between us and macaque monkeys show that this difficulty in stopping reactive responses is similar in our primate counterparts -- who during puberty, also show limitations in tests where they have to stop a reactive response. "The monkey is really the most powerful animal model that comes closest to the human condition," says Constantinidis. "They have a developed prefrontal cortex and follow a similar trajectory with the same patterns of maturation between adolescence and adulthood."

Taking risks and having thrilling adventures during this period isn't necessarily a bad thing. "You don't have this perfect inhibitory control system in adolescence, but that's happening for a reason. It has survived evolution because it's actually allowing for new experiences to provide information about the environment that is critical form optimal specialization of the brain to occur," Luna says. "Understanding the neural mechanisms that underlie this transitional period in our primate counterparts is critical to informing us about this period of brain and cognitive maturation."

Human neurological development during this time is characterized by changes in structural anatomy -- there is an active pruning of redundant and un-used neural connections and a strengthening of white matter tracts throughout the brain that will determine the template for how the adult brain will operate. Specifically, by adolescence all foundational aspects of brain organization are in place and during this time they undergo refinements that will enable the most optimal way to operate to deal with the demands of their specific environment.

In particular, the development of neural activity patterns that allow for the preparation of a response seems to be a key element of this phase of development -- and essential to successful performance on self-control tasks.

This all suggests that self-control isn't just about the ability, in the moment, to inhibit a behavior. "Executive function involves not only reflexive responses but actually being prepared ahead of time to create an appropriate plan. This is the change between the adolescent and adult brain and it is strikingly clear both in the human data and in the animal data," says Constantinidis.

Ultimately, the authors believe that this phase of development is essential to shaping the adult brain. "It is important for there to be a period where the animal or the human is actively encouraged to explore because gaining these new experiences will help mold what the adult trajectories are going to be," says Luna. ...

FULL STORY: https://www.sciencedaily.com/releases/2019/08/190820172110.htm
 
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