A cheerier article on human growth
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With His Bells and Curves, Human Growth Science Grew Up
By STEPHEN S. HALL
DUNKESWELL, England - Dr. Jim Tanner pored over two children's growth charts spread out on the table before him, observing the annual dots, casting an expert eye on where they landed amid the centiles and curves, lingering over the meager data about the 8-year-old girl, but venturing a tentative - and, to her father, namely me, an unnerving - conclusion.
"We're already seeing that she is going into early adolescence," Dr. Tanner mused, peering over his glasses. "Eight and a half, hmmm. Well, probably, probably, it's the beginning. That would be slightly early, but for a takeoff for a girl nowadays? I mean, a bit early. But normal, absolutely."
We were sitting in a 100-year-old coach house that had once been part of the Stentwood estate in Devonshire, two hours southwest of London by train, and 15 miles farther, by curving one-lane roads, hemmed in by encroaching hedgerows, from the train station in Taunton, the nearest big town.
It may seem like a long way to go to ask a doctor to look at a child's growth chart, especially when the doctor has been retired for 20 years. But Dr. James M. Tanner, even in retirement, remains one of the greatest experts on a subject everyone experiences but few think about, human growth.
Over a career that spanned half a century, Dr. Tanner helped bring the study of human growth into the era of modern biology. He helped create the first modern growth chart, has demonstrated the surprisingly powerful influence of environment upon the average size of national populations, and was among the first to argue that physical stature can shed enormous light on the quality of life of cultures both modern and ancient, findings that have revolutionized the field of economic history. On top of that, he is that rarest of academic creatures: a serious scientist who can legitimately claim to have been an Olympic-caliber athlete.
Although Dr. Tanner is largely unknown to the American public (with the exception of pediatricians familiar with the so-called "Tanner stages" of pubertal development), he is well known to his peers. Dr. David Barker, the British epidemiologist who has studied birth weight and early development, says flatly, "Jim is the god" of the field.
Dr. Robert Fogel, the Nobel Prize-winning University of Chicago economist whose research on the lives and health of American slaves was influenced by Dr. Tanner's work, said, "He's been one of the central figures in the biology of human growth, and the books he's written have become the central textbooks in the study of human growth."
Now 84, Dr. Tanner still discusses growth, the role of nurture versus nature in achieving maximum height, and a subtle - but, he believes, important - approach to data collection that explains differences between the growth charts that Dr. Tanner and his colleagues pioneered in the 1960's and the charts now in use in the United States.
Sophisticated modern statistical approaches to childhood growth, in the form of national growth charts, did not emerge until after World War II. The first government-issued national charts in the United States were released only in 1977 by the National Center for Health Statistics. The Centers for Disease Control and Prevention updated those charts in 2000.
Dr. Tanner and his colleagues at the Institute for Child Health in London revolutionized growth charts in the 1960's by taking into account variations in a child's tempo of growth. Rather than one-size-fits-all curves, the Tanner-derived charts have separate curves, with a separate set of percentiles, for early-, average- and late-maturing boys and girls. Thus they expand the range of normal growth, using curves that are more forgiving of individual variation, especially around the crucial time of puberty.
"At 8, she's dead on the 50th centile," he said of my daughter's growth data, "and what will happen now, dependent on when she has her growth spurt, she'll either go up like this" - his finger tracing an imaginary curve toward one adult height, "or she'll go up like that. But she will not go like that," he added, touching on the dark 50th centile curve on the chart.
"I think the deep, fundamental point in all this," Dr. Tanner continued, "is differences in the rate of maturation. A child is small at a certain age. Is he small because he's small and he's going to be small unless he does something about it? Because another child, of the same height and the same age and the same smallness, is just delayed in his maturation. Perfectly normal. And will end up exactly average."
These subtle differences derive from the kind of data used to create a growth chart. The American charts (and some modern European charts) primarily rely on cross-sectional data: researchers take a large group of children, separate them by age, measure them one time and then plot the distribution of heights and weights for each age group.
In contrast, Dr. Tanner and others believe a more accurate (and flexible) picture of a child's growth emerges from so-called longitudinal studies, where the same children are repeatedly measured over the course of many years of growth, so that individual variations in tempo - those who mature early and those who mature late - can be statistically incorporated into the charts. The data for such charts are more logistically difficult and costly to collect. But some growth experts believe such charts provide a more realistic picture of variation in individual growth patterns.
To make the point, Dr. Tanner fetched one of his charts. There were three different curves representing variations on normality. One, in red, showed the trajectory of an early-maturing girl. The second, in black, showed the trajectory of girls maturing "on time." The third, in green, showed the trajectory of late-maturing.
"So you see, at age 2 they're pretty much the same," Dr. Tanner said, pointing out a common starting point for three starkly different growth trajectories. "But you get a very big effect later on."
At 11 years old, the 50th centile late maturer is nearly seven inches shorter than the early maturer, he said. "But," he added, "a few years later, they're identical."
"There are more ways of being normal than are shown here," Dr. Tanner said, nodding toward the American-style charts. This philosophical difference has always been controversial, although other experts agree with Dr. Tanner, to a point. "He's absolutely right" about the limitations of cross-sectional charts, said Dr. Alan D. Rogol, a growth expert in Charlottesville, Va.
"You mush things together when you make a growth curve for a population," Dr. Rogol said. "But for clinical work, I think the differences are not all that great. It's a tempest in a teapot."
The Tanner-inspired longitudinal charts are still sold and used in England, but he said their use had been overshadowed by cross-sectional charts distributed by drug companies or growth foundations that receive financing from companies that make human growth hormone, the use of which has exploded in recent years.
Asked if cross-sectional charts made the use of growth hormone more likely, Dr. Tanner said it would "if you're simple-minded."
"You're going to treat late maturers, lots and lots," he said.
Born in 1920, Jim Tanner grew up partly in Egypt and China; his father was a career army officer. He attended St. Mary's School of Medicine in London on something like an athletic scholarship, having agreed to teach his fellow students physical education. He was the fastest junior British runner in the 110-meter hurdles in 1939, and trained with Britain's pre-Olympics track team. In all likelihood, he would have competed in the 1940 Olympics, had it not been for the war.
He was among a handful of British medical students brought to the United States by the Rockefeller Foundation to complete their studies. He received his medical degree from the University of Pennsylvania, did his internship at Johns Hopkins and met his first wife, Dr. Bernice Alture, a Brooklyn-born general practitioner who also graduated from Penn. (She died in 1991.)
The origins of the modern longitudinal growth chart began in 1948, when Dr. Tanner was approached by the British government and asked to take over a study of childhood growth that began during the war. The study, focused on orphans living in a home in Harpenden, north of London, was initially intended to observe the effects of wartime malnutrition on growth. But it evolved into the Harpenden Growth Study, the earliest of the longitudinal studies in postwar Europe.
To develop the methodology of what would become the first modern growth chart, Dr. Tanner traveled to the United States and met with growth experts. In his research, he realized that several prominent American growth experts - including Dr. Franz Boas, the legendary physical anthropologist, and Dr. Nancy Bayley, the psychologist at the University of California, Berkeley - had understood the crucial importance of tempo of growth. But Dr. Tanner also discovered that their work had been largely ignored by their colleagues.
"We built this thing up, having just paid attention to what Boas and Bayley were teaching us," Dr. Tanner recalled. He continued to work on the Harpenden survey with his longtime associate, Reginald Whitehouse, until 1971. Once a month, the two researchers traveled to Harpenden, measured the children and took pictures, and later expanded the research to include data from other European surveys. Their first chart came out in the early 1960's.
In the same era, he was responsible for choosing the five or six children in Britain who qualified for injections of human growth hormone, then rare and harvested only from human cadavers. In 1985, when several patients in the United States and Britain died from an infectious brain disease spread through cadaveric growth hormone, injections were immediately suspended.
Still, some families objected. "Some parents, amazingly, said, 'We'll take the risk.' " Dr. Tanner recalled.
"We didn't accede," he added.
Treatments resumed only when genetically engineered human growth hormone became available the next year. In the 1990's, Dr. Tanner set out to write a new overview of growth, but soon abandoned the project. "I realized that the time had passed when a single person could write a textbook on growth," he said. "It just is not possible."
So his semi-retirement became permanent. "I would not consider myself an expert anymore," he said.
I'll also throw in one on personality.
Looking for Personality in Animals, of All People
By CARL ZIMMER
A team of Dutch scientists is trying to solve the mystery of personality. Why are some individuals shy while others are bold, for example? What roles do genes and environment play in shaping personalities? And most mysterious of all, how did they evolve?
The scientists are carrying out an ambitious series of experiments to answer these questions. They are studying thousands of individuals, observing how they interact with others, comparing their personalities to their descendants' and analyzing their DNA.
It may come as a surprise that their subjects have feathers. The scientists, based at the Netherlands Institute of Ecology, are investigating personalities of wild birds.
Until recently, most experts in personality would have considered such a study as nothing but foolish anthropomorphism. "It's been looked at with suspicion and contempt," said Dr. Samuel Gosling, a psychologist at the University of Texas.
But scientists have found that in many species, individual animals behave in consistently different ways. They argue that these differences meet the scientific definition of personality.
If they are right, then human personality has deep evolutionary roots. "It's a matter of degree, not of differences," said Dr. Piet Drent of the Netherlands Institute of Ecology.
The bird study that Dr. Drent and his colleagues are conducting is considered the most ambitious investigation of personality in wild animals.
"They've gone the furthest," said Dr. Sasha Dall, an evolutionary biologist at the University of Exeter in Cornwall.
The Dutch researchers are studying the importance of genes to the personalities of the birds, and the effect different personalities have on their survival. They hope next to carry out parallel studies in humans to see whether the same forces behind the evolution of bird personalities are at work in our own species.
The science of human personality is about a century old. Psychologists have relied largely on questionnaires and other testing methods to map out its dimensions. One common method is for scientists to ask their subjects how well certain adjectives apply to themselves (or to people they know well).
"Certain traits tend to go together," Dr. Gosling said. "We find that people who are energetic also tend to be talkative. It needn't be that way, but that's how it tends to be." The flip side is true as well: less energetic people tend to be less talkative.
Psychologists have found they can bundle these traits into just a few personality dimensions. People may be more or less extroverted, for example, which means they are sociable, assertive and tend to have positive emotions. The same dimensions have been documented across the world, from Zimbabwe to the Russian Arctic, suggesting that they are universal in humans.
Some studies have suggested that genes are responsible for some of the differences in people's personality ratings. But they have been far from conclusive because scientists cannot do experiments with humans. "Human mothers will not let you just swap their infants at birth, which would be a great study to do," Dr. Gosling said.
It has been only in the last decade or so that scientists have investigated whether animals have personalities. In one pioneering study in the mid-1990's, Dr. Gosling studied a colony of 34 hyenas at the University of California, Berkeley. "My goal was simply to say, can we measure personality in animals? It wasn't clear it was going to work," he said.
Dr. Gosling asked the four caretakers of the colony to fill out a modified version of the human questionnaire for each animal.
"It turned out that they agreed at the level you find in humans," Dr. Gosling said. What's more, the hyena personalities fit some of the dimensions found in humans, like neuroticism and agreeableness. Since then, a number of other studies have documented personalities in animals ranging from chimpanzees to squid.
To some biologists, the main question about these animal personalities is why natural selection keeps such a wide range of them. "Why hasn't one personality become the standard in the population?" asked Dr. Drent. If being extroverted offers the best odds for a hyena to reproduce, you might expect that over time, all hyenas would wind up as extroverts.
Dr. Drent and his colleagues hope that their study on birds may reveal some clues. They are studying a European relative of chickadees called the great tit (Parus major). Most of the birds spend their entire lives in a single forest, and they are happy to move into comfortable nest boxes provided by the scientists. As a result, the Dutch researchers can track the entire population of birds for years, keeping tabs on their health and their success at reproducing.
The scientists can also bring some of the birds into the lab in order to measure their personalities or carry out breeding experiments.
"These birds are perfect for these sorts of studies," said Dr. Niels Dingemanse of the University of Groningen, a collaborator Dr. Drent.
Instead of questionnaires, the Dutch team tests the behavior of the birds to measure their personalities. In one test, the scientists place a strange object - a penlight battery or a Pink Panther doll - in a bird's cage. Some birds are quick to approach it, while others hang back.
In another experiment, the researchers open a cage door, allowing the birds to explore a large room filled with five artificial trees. Some birds are quick to explore the trees, while others prefer to remain in the comforts of their cage.
In a third experiment, the researchers place a bowl of tasty mealy worms in the room. When the birds land on the bowl to eat, the researchers startle the birds by lifting up a nearby metal plate. They then see how much time passes before the bird returns to the bowl.
The tests revealed that the birds have consistent personalities that remain stable for years. Bold birds, as the scientists call them, are quick to inspect new objects, to explore the trees and to recover from the metal-plate surprise.
Shy birds are slow on all three counts. The differences go well beyond these tests. Bold birds are also more aggressive than shy ones and experience less stress when the scientists handle them.
Breeding experiments revealed that these traits had a strong genetic basis. Over just four generations, the researchers could produce significantly bolder and shyer birds. "About 50 percent of the variation you find in avian personalities is due to differences in genes," said Dr. Kees van Oers of the Max Planck Institute for Ornithology in Germany.
Dr. van Oers is searching for the genes responsible for these differences. He estimates that as many as 10 may play an important role, and he has already pinpointed one strong candidate, known as DRD4.
Some studies on the human version of this gene suggest that it influences how much people seek out new experiences. But other studies have failed to replicate the link. "We're still working on the last bits, but it looks promising," Dr. van Oers said.
The genes for both bold and shy traits have been preserved by natural selection. To find out how this happens, the researchers have observed how birds with different traits have fared over the years. "We were not sure how the data would turn out because no one had collected them before," said Dr. Dingemanse, who led this part of the study.
The researchers found that the personality of birds had a powerful effect on their survival, but that effect changed from year to year as the supply of food fluctuated. "It's quite a complex story," Dr. Dingemanse said. In lean years, for example, bold female birds had a better chance of surviving than shy ones, while shy males did better than bold ones. Those patterns switched during years with abundant food.
Over the course of several years, however, birds with intermediate personalities appear to have had more success at bearing young. "Animals in the middle did better," Dr. Dingemanse said.
If intermediate birds are better adapted than very bold or shy ones, it is strange that all the birds are not intermediate. One possibility is intermediate personalities arise when birds inherit a "bold" version of certain genes from one parent and a "shy" version from the other.
Since a bird has a 50 percent chance of inheriting a gene from its mother or father, it's inevitable that some will wind up with two "shy" genes or two "bold" ones. As a result, they may get extreme personalities.
Another idea the Dutch scientists want to explore is that the social life of birds helps bold and shy personalities to coexist.
Each year the birds fight for territory where they can feed and breed. Bold birds are more aggressive than shy ones, and that sometimes helps them win territory. But the scientists have found that when bold birds lose, they are slow to recover. They end up at the bottom of the hierarchy, and in many cases just fly away. "They go to other places to try to become No. 1," Dr. Drent said.
This struggle might balance the birds between bold and shy personalities. If there are a lot of shy birds, the few bold ones will rise to the top. But if there are a lot of bold birds, they will fight a lot, and that will result in a lot of bold birds flying away. In these cases, the few shy birds will thrive. "So one of the personalities can never disappear completely," Dr. Drent said.
He and his colleagues plan to test this hypothesis by altering the ratio of bold and shy birds in the wild.
Many of the findings are summarized in the February issue of Neuroscience and Biobehavioral Reviews.
Researchers studying animal personality hope that their work will yield some practical benefits. Dr. Gosling and his students, for example, have been focusing much of their research on the personalities of dogs.
An accurate test of dog personality may help animal shelters match pets to families. It may also help identify dogs that are especially well suited to jobs like detecting explosives.
Studies on animal personality may also illuminate human personality. The Dutch researchers are now beginning to compare their research on birds to research carried out on children.
"It was amazing how the way they measured the boldness of the birds resembles tests we have for young children," said Dr. Marcel van Aken, a psychologist at the University of Utrecht. He and the bird researchers plan to measure the personalities of birds and humans with a common set of tests, hoping to find clues to the evolution of human personality.
Barely any research has been carried out on the evolution of human personality, but what little there is suggests that it may have some parallels with what's happened in birds.
In a survey of 545 people, Dr. Daniel Nettle of the University of Newcastle in England found that the more extroverted people were, the more sex partners they tended to have had. That might give them an evolutionary edge, but Dr. Nettle found that they were also more likely to wind up in a hospital.
Dr. Nettle is reporting his findings in a paper to be published in Evolution and Human Behavior.
Some experts on human personality remain skeptical. Dr. Daniel Cervone of the University of Illinois at Chicago considers describing animals with terms like extroversion as "extremely risky." The word inevitably means something different when applied to a human or a bird.
"There's a whole load of human qualities that simply weren't going into the ratings in the first place," he said.
Dr. van Aken agrees that anthropomorphism is a real danger, but he thinks it can be avoided. "I'm not so concerned about it," he says. "You have to define clearly what you are going to measure and then let the data speak."
With His Bells and Curves, Human Growth Science Grew Up
By STEPHEN S. HALL
DUNKESWELL, England - Dr. Jim Tanner pored over two children's growth charts spread out on the table before him, observing the annual dots, casting an expert eye on where they landed amid the centiles and curves, lingering over the meager data about the 8-year-old girl, but venturing a tentative - and, to her father, namely me, an unnerving - conclusion.
"We're already seeing that she is going into early adolescence," Dr. Tanner mused, peering over his glasses. "Eight and a half, hmmm. Well, probably, probably, it's the beginning. That would be slightly early, but for a takeoff for a girl nowadays? I mean, a bit early. But normal, absolutely."
We were sitting in a 100-year-old coach house that had once been part of the Stentwood estate in Devonshire, two hours southwest of London by train, and 15 miles farther, by curving one-lane roads, hemmed in by encroaching hedgerows, from the train station in Taunton, the nearest big town.
It may seem like a long way to go to ask a doctor to look at a child's growth chart, especially when the doctor has been retired for 20 years. But Dr. James M. Tanner, even in retirement, remains one of the greatest experts on a subject everyone experiences but few think about, human growth.
Over a career that spanned half a century, Dr. Tanner helped bring the study of human growth into the era of modern biology. He helped create the first modern growth chart, has demonstrated the surprisingly powerful influence of environment upon the average size of national populations, and was among the first to argue that physical stature can shed enormous light on the quality of life of cultures both modern and ancient, findings that have revolutionized the field of economic history. On top of that, he is that rarest of academic creatures: a serious scientist who can legitimately claim to have been an Olympic-caliber athlete.
Although Dr. Tanner is largely unknown to the American public (with the exception of pediatricians familiar with the so-called "Tanner stages" of pubertal development), he is well known to his peers. Dr. David Barker, the British epidemiologist who has studied birth weight and early development, says flatly, "Jim is the god" of the field.
Dr. Robert Fogel, the Nobel Prize-winning University of Chicago economist whose research on the lives and health of American slaves was influenced by Dr. Tanner's work, said, "He's been one of the central figures in the biology of human growth, and the books he's written have become the central textbooks in the study of human growth."
Now 84, Dr. Tanner still discusses growth, the role of nurture versus nature in achieving maximum height, and a subtle - but, he believes, important - approach to data collection that explains differences between the growth charts that Dr. Tanner and his colleagues pioneered in the 1960's and the charts now in use in the United States.
Sophisticated modern statistical approaches to childhood growth, in the form of national growth charts, did not emerge until after World War II. The first government-issued national charts in the United States were released only in 1977 by the National Center for Health Statistics. The Centers for Disease Control and Prevention updated those charts in 2000.
Dr. Tanner and his colleagues at the Institute for Child Health in London revolutionized growth charts in the 1960's by taking into account variations in a child's tempo of growth. Rather than one-size-fits-all curves, the Tanner-derived charts have separate curves, with a separate set of percentiles, for early-, average- and late-maturing boys and girls. Thus they expand the range of normal growth, using curves that are more forgiving of individual variation, especially around the crucial time of puberty.
"At 8, she's dead on the 50th centile," he said of my daughter's growth data, "and what will happen now, dependent on when she has her growth spurt, she'll either go up like this" - his finger tracing an imaginary curve toward one adult height, "or she'll go up like that. But she will not go like that," he added, touching on the dark 50th centile curve on the chart.
"I think the deep, fundamental point in all this," Dr. Tanner continued, "is differences in the rate of maturation. A child is small at a certain age. Is he small because he's small and he's going to be small unless he does something about it? Because another child, of the same height and the same age and the same smallness, is just delayed in his maturation. Perfectly normal. And will end up exactly average."
These subtle differences derive from the kind of data used to create a growth chart. The American charts (and some modern European charts) primarily rely on cross-sectional data: researchers take a large group of children, separate them by age, measure them one time and then plot the distribution of heights and weights for each age group.
In contrast, Dr. Tanner and others believe a more accurate (and flexible) picture of a child's growth emerges from so-called longitudinal studies, where the same children are repeatedly measured over the course of many years of growth, so that individual variations in tempo - those who mature early and those who mature late - can be statistically incorporated into the charts. The data for such charts are more logistically difficult and costly to collect. But some growth experts believe such charts provide a more realistic picture of variation in individual growth patterns.
To make the point, Dr. Tanner fetched one of his charts. There were three different curves representing variations on normality. One, in red, showed the trajectory of an early-maturing girl. The second, in black, showed the trajectory of girls maturing "on time." The third, in green, showed the trajectory of late-maturing.
"So you see, at age 2 they're pretty much the same," Dr. Tanner said, pointing out a common starting point for three starkly different growth trajectories. "But you get a very big effect later on."
At 11 years old, the 50th centile late maturer is nearly seven inches shorter than the early maturer, he said. "But," he added, "a few years later, they're identical."
"There are more ways of being normal than are shown here," Dr. Tanner said, nodding toward the American-style charts. This philosophical difference has always been controversial, although other experts agree with Dr. Tanner, to a point. "He's absolutely right" about the limitations of cross-sectional charts, said Dr. Alan D. Rogol, a growth expert in Charlottesville, Va.
"You mush things together when you make a growth curve for a population," Dr. Rogol said. "But for clinical work, I think the differences are not all that great. It's a tempest in a teapot."
The Tanner-inspired longitudinal charts are still sold and used in England, but he said their use had been overshadowed by cross-sectional charts distributed by drug companies or growth foundations that receive financing from companies that make human growth hormone, the use of which has exploded in recent years.
Asked if cross-sectional charts made the use of growth hormone more likely, Dr. Tanner said it would "if you're simple-minded."
"You're going to treat late maturers, lots and lots," he said.
Born in 1920, Jim Tanner grew up partly in Egypt and China; his father was a career army officer. He attended St. Mary's School of Medicine in London on something like an athletic scholarship, having agreed to teach his fellow students physical education. He was the fastest junior British runner in the 110-meter hurdles in 1939, and trained with Britain's pre-Olympics track team. In all likelihood, he would have competed in the 1940 Olympics, had it not been for the war.
He was among a handful of British medical students brought to the United States by the Rockefeller Foundation to complete their studies. He received his medical degree from the University of Pennsylvania, did his internship at Johns Hopkins and met his first wife, Dr. Bernice Alture, a Brooklyn-born general practitioner who also graduated from Penn. (She died in 1991.)
The origins of the modern longitudinal growth chart began in 1948, when Dr. Tanner was approached by the British government and asked to take over a study of childhood growth that began during the war. The study, focused on orphans living in a home in Harpenden, north of London, was initially intended to observe the effects of wartime malnutrition on growth. But it evolved into the Harpenden Growth Study, the earliest of the longitudinal studies in postwar Europe.
To develop the methodology of what would become the first modern growth chart, Dr. Tanner traveled to the United States and met with growth experts. In his research, he realized that several prominent American growth experts - including Dr. Franz Boas, the legendary physical anthropologist, and Dr. Nancy Bayley, the psychologist at the University of California, Berkeley - had understood the crucial importance of tempo of growth. But Dr. Tanner also discovered that their work had been largely ignored by their colleagues.
"We built this thing up, having just paid attention to what Boas and Bayley were teaching us," Dr. Tanner recalled. He continued to work on the Harpenden survey with his longtime associate, Reginald Whitehouse, until 1971. Once a month, the two researchers traveled to Harpenden, measured the children and took pictures, and later expanded the research to include data from other European surveys. Their first chart came out in the early 1960's.
In the same era, he was responsible for choosing the five or six children in Britain who qualified for injections of human growth hormone, then rare and harvested only from human cadavers. In 1985, when several patients in the United States and Britain died from an infectious brain disease spread through cadaveric growth hormone, injections were immediately suspended.
Still, some families objected. "Some parents, amazingly, said, 'We'll take the risk.' " Dr. Tanner recalled.
"We didn't accede," he added.
Treatments resumed only when genetically engineered human growth hormone became available the next year. In the 1990's, Dr. Tanner set out to write a new overview of growth, but soon abandoned the project. "I realized that the time had passed when a single person could write a textbook on growth," he said. "It just is not possible."
So his semi-retirement became permanent. "I would not consider myself an expert anymore," he said.
I'll also throw in one on personality.
Looking for Personality in Animals, of All People
By CARL ZIMMER
A team of Dutch scientists is trying to solve the mystery of personality. Why are some individuals shy while others are bold, for example? What roles do genes and environment play in shaping personalities? And most mysterious of all, how did they evolve?
The scientists are carrying out an ambitious series of experiments to answer these questions. They are studying thousands of individuals, observing how they interact with others, comparing their personalities to their descendants' and analyzing their DNA.
It may come as a surprise that their subjects have feathers. The scientists, based at the Netherlands Institute of Ecology, are investigating personalities of wild birds.
Until recently, most experts in personality would have considered such a study as nothing but foolish anthropomorphism. "It's been looked at with suspicion and contempt," said Dr. Samuel Gosling, a psychologist at the University of Texas.
But scientists have found that in many species, individual animals behave in consistently different ways. They argue that these differences meet the scientific definition of personality.
If they are right, then human personality has deep evolutionary roots. "It's a matter of degree, not of differences," said Dr. Piet Drent of the Netherlands Institute of Ecology.
The bird study that Dr. Drent and his colleagues are conducting is considered the most ambitious investigation of personality in wild animals.
"They've gone the furthest," said Dr. Sasha Dall, an evolutionary biologist at the University of Exeter in Cornwall.
The Dutch researchers are studying the importance of genes to the personalities of the birds, and the effect different personalities have on their survival. They hope next to carry out parallel studies in humans to see whether the same forces behind the evolution of bird personalities are at work in our own species.
The science of human personality is about a century old. Psychologists have relied largely on questionnaires and other testing methods to map out its dimensions. One common method is for scientists to ask their subjects how well certain adjectives apply to themselves (or to people they know well).
"Certain traits tend to go together," Dr. Gosling said. "We find that people who are energetic also tend to be talkative. It needn't be that way, but that's how it tends to be." The flip side is true as well: less energetic people tend to be less talkative.
Psychologists have found they can bundle these traits into just a few personality dimensions. People may be more or less extroverted, for example, which means they are sociable, assertive and tend to have positive emotions. The same dimensions have been documented across the world, from Zimbabwe to the Russian Arctic, suggesting that they are universal in humans.
Some studies have suggested that genes are responsible for some of the differences in people's personality ratings. But they have been far from conclusive because scientists cannot do experiments with humans. "Human mothers will not let you just swap their infants at birth, which would be a great study to do," Dr. Gosling said.
It has been only in the last decade or so that scientists have investigated whether animals have personalities. In one pioneering study in the mid-1990's, Dr. Gosling studied a colony of 34 hyenas at the University of California, Berkeley. "My goal was simply to say, can we measure personality in animals? It wasn't clear it was going to work," he said.
Dr. Gosling asked the four caretakers of the colony to fill out a modified version of the human questionnaire for each animal.
"It turned out that they agreed at the level you find in humans," Dr. Gosling said. What's more, the hyena personalities fit some of the dimensions found in humans, like neuroticism and agreeableness. Since then, a number of other studies have documented personalities in animals ranging from chimpanzees to squid.
To some biologists, the main question about these animal personalities is why natural selection keeps such a wide range of them. "Why hasn't one personality become the standard in the population?" asked Dr. Drent. If being extroverted offers the best odds for a hyena to reproduce, you might expect that over time, all hyenas would wind up as extroverts.
Dr. Drent and his colleagues hope that their study on birds may reveal some clues. They are studying a European relative of chickadees called the great tit (Parus major). Most of the birds spend their entire lives in a single forest, and they are happy to move into comfortable nest boxes provided by the scientists. As a result, the Dutch researchers can track the entire population of birds for years, keeping tabs on their health and their success at reproducing.
The scientists can also bring some of the birds into the lab in order to measure their personalities or carry out breeding experiments.
"These birds are perfect for these sorts of studies," said Dr. Niels Dingemanse of the University of Groningen, a collaborator Dr. Drent.
Instead of questionnaires, the Dutch team tests the behavior of the birds to measure their personalities. In one test, the scientists place a strange object - a penlight battery or a Pink Panther doll - in a bird's cage. Some birds are quick to approach it, while others hang back.
In another experiment, the researchers open a cage door, allowing the birds to explore a large room filled with five artificial trees. Some birds are quick to explore the trees, while others prefer to remain in the comforts of their cage.
In a third experiment, the researchers place a bowl of tasty mealy worms in the room. When the birds land on the bowl to eat, the researchers startle the birds by lifting up a nearby metal plate. They then see how much time passes before the bird returns to the bowl.
The tests revealed that the birds have consistent personalities that remain stable for years. Bold birds, as the scientists call them, are quick to inspect new objects, to explore the trees and to recover from the metal-plate surprise.
Shy birds are slow on all three counts. The differences go well beyond these tests. Bold birds are also more aggressive than shy ones and experience less stress when the scientists handle them.
Breeding experiments revealed that these traits had a strong genetic basis. Over just four generations, the researchers could produce significantly bolder and shyer birds. "About 50 percent of the variation you find in avian personalities is due to differences in genes," said Dr. Kees van Oers of the Max Planck Institute for Ornithology in Germany.
Dr. van Oers is searching for the genes responsible for these differences. He estimates that as many as 10 may play an important role, and he has already pinpointed one strong candidate, known as DRD4.
Some studies on the human version of this gene suggest that it influences how much people seek out new experiences. But other studies have failed to replicate the link. "We're still working on the last bits, but it looks promising," Dr. van Oers said.
The genes for both bold and shy traits have been preserved by natural selection. To find out how this happens, the researchers have observed how birds with different traits have fared over the years. "We were not sure how the data would turn out because no one had collected them before," said Dr. Dingemanse, who led this part of the study.
The researchers found that the personality of birds had a powerful effect on their survival, but that effect changed from year to year as the supply of food fluctuated. "It's quite a complex story," Dr. Dingemanse said. In lean years, for example, bold female birds had a better chance of surviving than shy ones, while shy males did better than bold ones. Those patterns switched during years with abundant food.
Over the course of several years, however, birds with intermediate personalities appear to have had more success at bearing young. "Animals in the middle did better," Dr. Dingemanse said.
If intermediate birds are better adapted than very bold or shy ones, it is strange that all the birds are not intermediate. One possibility is intermediate personalities arise when birds inherit a "bold" version of certain genes from one parent and a "shy" version from the other.
Since a bird has a 50 percent chance of inheriting a gene from its mother or father, it's inevitable that some will wind up with two "shy" genes or two "bold" ones. As a result, they may get extreme personalities.
Another idea the Dutch scientists want to explore is that the social life of birds helps bold and shy personalities to coexist.
Each year the birds fight for territory where they can feed and breed. Bold birds are more aggressive than shy ones, and that sometimes helps them win territory. But the scientists have found that when bold birds lose, they are slow to recover. They end up at the bottom of the hierarchy, and in many cases just fly away. "They go to other places to try to become No. 1," Dr. Drent said.
This struggle might balance the birds between bold and shy personalities. If there are a lot of shy birds, the few bold ones will rise to the top. But if there are a lot of bold birds, they will fight a lot, and that will result in a lot of bold birds flying away. In these cases, the few shy birds will thrive. "So one of the personalities can never disappear completely," Dr. Drent said.
He and his colleagues plan to test this hypothesis by altering the ratio of bold and shy birds in the wild.
Many of the findings are summarized in the February issue of Neuroscience and Biobehavioral Reviews.
Researchers studying animal personality hope that their work will yield some practical benefits. Dr. Gosling and his students, for example, have been focusing much of their research on the personalities of dogs.
An accurate test of dog personality may help animal shelters match pets to families. It may also help identify dogs that are especially well suited to jobs like detecting explosives.
Studies on animal personality may also illuminate human personality. The Dutch researchers are now beginning to compare their research on birds to research carried out on children.
"It was amazing how the way they measured the boldness of the birds resembles tests we have for young children," said Dr. Marcel van Aken, a psychologist at the University of Utrecht. He and the bird researchers plan to measure the personalities of birds and humans with a common set of tests, hoping to find clues to the evolution of human personality.
Barely any research has been carried out on the evolution of human personality, but what little there is suggests that it may have some parallels with what's happened in birds.
In a survey of 545 people, Dr. Daniel Nettle of the University of Newcastle in England found that the more extroverted people were, the more sex partners they tended to have had. That might give them an evolutionary edge, but Dr. Nettle found that they were also more likely to wind up in a hospital.
Dr. Nettle is reporting his findings in a paper to be published in Evolution and Human Behavior.
Some experts on human personality remain skeptical. Dr. Daniel Cervone of the University of Illinois at Chicago considers describing animals with terms like extroversion as "extremely risky." The word inevitably means something different when applied to a human or a bird.
"There's a whole load of human qualities that simply weren't going into the ratings in the first place," he said.
Dr. van Aken agrees that anthropomorphism is a real danger, but he thinks it can be avoided. "I'm not so concerned about it," he says. "You have to define clearly what you are going to measure and then let the data speak."
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no subject
Date: 2005-03-01 12:25 am (UTC)no subject
Date: 2005-03-01 10:24 am (UTC)http://www.nature.com/news/2004/040119/pf/040119-2_pf.html
http://dx.doi.org/10.1037%2F0022-3514.85.6.1161
Gosling asked dog owners to rate their pet on four different personality traits. The traits, which are also found in humans, have positive and negative extremes - for example, dogs could be rated as energetic, slothful or somewhere in between. The other traits were affection-aggression, anxiety-calmness and intelligence-stupidity.
Strangers then watched the animals perform tasks in a local park, and rated them on the same characteristics. Anxiety, for example, was assessed from the dog's reaction as it watched its owner walk away with another hound. The ability to retrieve a hidden treat from under a cup was used as a measure of intelligence.
In total, 78 dogs of all shapes and sizes were tested. In general, owners and strangers agreed on an individual dog's personality. This suggests that the dog personalities are real, says Gosling.
no subject
Date: 2005-03-01 12:25 am (UTC)no subject
Date: 2005-03-01 10:24 am (UTC)http://www.nature.com/news/2004/040119/pf/040119-2_pf.html
http://dx.doi.org/10.1037%2F0022-3514.85.6.1161
Gosling asked dog owners to rate their pet on four different personality traits. The traits, which are also found in humans, have positive and negative extremes - for example, dogs could be rated as energetic, slothful or somewhere in between. The other traits were affection-aggression, anxiety-calmness and intelligence-stupidity.
Strangers then watched the animals perform tasks in a local park, and rated them on the same characteristics. Anxiety, for example, was assessed from the dog's reaction as it watched its owner walk away with another hound. The ability to retrieve a hidden treat from under a cup was used as a measure of intelligence.
In total, 78 dogs of all shapes and sizes were tested. In general, owners and strangers agreed on an individual dog's personality. This suggests that the dog personalities are real, says Gosling.