Welcome to Your Child's Brain: How the Mind Grows From Conception to College by Sam Wang, Sandra Aamodt Page B
Authors: Sam Wang, Sandra Aamodt
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shows the differences between groups that correspond to typical d' values. The horizontal axis represents the possible scores, while the height of the curve represents the number of people in the population who get a particular score. From top to bottom, these differences would be considered small, medium, and very large.
Let’s consider some specific examples. For gender differences in adult height in the U.S., the left curve in the bottom panel (d' = 1.9) would represent women, and the right curve would represent men. The horizontal axis would show heights from short (left) to tall (right), with the peak of the female curve at 5 feet 3.8 inches, the average height for women, and the peak of the male curve at 5 feet 9.4 inches, the average height for men. A man of average height is taller than 92 percent of women. In the research literature, a value of d' that is at least 0.8 is considered large, so this would be a very large difference.
At the other extreme, let’s take as our example a small difference that we’ve already mentioned: hearing. Several authors have recently argued in favor of single-sex education based in part on the idea that girls have more sensitive hearing than boys and therefore respond best to teachers speaking quietly. For hearing sensitivity, the left curve in the top panel (d' = 0.2) would represent boys, and the right curve would represent girls. Because the difference between the two groups is small, as you can see, the two curves overlap substantially.
The individual differences in hearing within each sex are much larger than the differences between boys and girls. And given that many boys have sharper hearing than many girls, it doesn’t make sense to argue for sex segregation on these grounds. If you think sensitive hearing affects the way people learn, you should separate them based on their hearing, not their gender—the two are not the same.
Only a few gender differences are big enough to predict individual behavior. The largest known behavioral difference at any age is toy preferences in three-year-olds. Parents who try to keep their sons from playing with toy guns often discover that any stick—or, in a pinch, even a doll—can be converted to a weapon in a boy’s imagination. Given the choice between a boy-typical toy like a car and a girl-typical toy like a tea set, at age three children differ in their choice of boyish toys with a d' of 1.9, a difference corresponding to the bottom panel of the figure. This means that you can do quite well at guessing the sex of a young child based on his or her choice of toys, as 97 percent of boys are more likely to play with male-typical toys than an average girl. Because play helps children learn and practice a variety of skills, sex differences in how children spend their timecan influence which abilities they carry through life (see Practical tip: Broadening your child’s abilities ).
The emergence of toy preferences is an early stage in the development of gender identity , defined as your child’s self-identification as male or female. Gender-influenced toy preferences are seen across cultures, beginning around one year of age. Even babies have some understanding of gender (see chapter 1 ), but only a few two-year-old children can accurately state whether they are boys or girls or reliably distinguish men from women in pictures. Most children—again across cultures—reach this milestone by two and a half, and almost all children get there by age three. Children who have reached this milestone are less likely to choose the “wrong” toy than children who have not.
Toy preferences almost certainly have an innate basis (though they are also influenced by culture). One clue is that male monkeys prefer to play with trucks, while female monkeys prefer dolls. Another clue is that boy-typical toy preferences are more common in girls with a syndrome called congenital adrenal hyperplasia or CAH . Due to a genetic defect in adrenal hormone
Let’s consider some specific examples. For gender differences in adult height in the U.S., the left curve in the bottom panel (d' = 1.9) would represent women, and the right curve would represent men. The horizontal axis would show heights from short (left) to tall (right), with the peak of the female curve at 5 feet 3.8 inches, the average height for women, and the peak of the male curve at 5 feet 9.4 inches, the average height for men. A man of average height is taller than 92 percent of women. In the research literature, a value of d' that is at least 0.8 is considered large, so this would be a very large difference.
At the other extreme, let’s take as our example a small difference that we’ve already mentioned: hearing. Several authors have recently argued in favor of single-sex education based in part on the idea that girls have more sensitive hearing than boys and therefore respond best to teachers speaking quietly. For hearing sensitivity, the left curve in the top panel (d' = 0.2) would represent boys, and the right curve would represent girls. Because the difference between the two groups is small, as you can see, the two curves overlap substantially.
The individual differences in hearing within each sex are much larger than the differences between boys and girls. And given that many boys have sharper hearing than many girls, it doesn’t make sense to argue for sex segregation on these grounds. If you think sensitive hearing affects the way people learn, you should separate them based on their hearing, not their gender—the two are not the same.
Only a few gender differences are big enough to predict individual behavior. The largest known behavioral difference at any age is toy preferences in three-year-olds. Parents who try to keep their sons from playing with toy guns often discover that any stick—or, in a pinch, even a doll—can be converted to a weapon in a boy’s imagination. Given the choice between a boy-typical toy like a car and a girl-typical toy like a tea set, at age three children differ in their choice of boyish toys with a d' of 1.9, a difference corresponding to the bottom panel of the figure. This means that you can do quite well at guessing the sex of a young child based on his or her choice of toys, as 97 percent of boys are more likely to play with male-typical toys than an average girl. Because play helps children learn and practice a variety of skills, sex differences in how children spend their timecan influence which abilities they carry through life (see Practical tip: Broadening your child’s abilities ).
The emergence of toy preferences is an early stage in the development of gender identity , defined as your child’s self-identification as male or female. Gender-influenced toy preferences are seen across cultures, beginning around one year of age. Even babies have some understanding of gender (see chapter 1 ), but only a few two-year-old children can accurately state whether they are boys or girls or reliably distinguish men from women in pictures. Most children—again across cultures—reach this milestone by two and a half, and almost all children get there by age three. Children who have reached this milestone are less likely to choose the “wrong” toy than children who have not.
Toy preferences almost certainly have an innate basis (though they are also influenced by culture). One clue is that male monkeys prefer to play with trucks, while female monkeys prefer dolls. Another clue is that boy-typical toy preferences are more common in girls with a syndrome called congenital adrenal hyperplasia or CAH . Due to a genetic defect in adrenal hormone
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