• Gender Does Not Equal Biological Sex
• Biological sex, the physical aspects of being male or female, is different from gender, the social
differences between being male or female.
– Most people feel that their gender matches their biological sex.
But approximately 1 percent to 3 percent of the population reports being transgender, meaning they feel
their gender is different from their biological sex
• In addition, gender can extend beyond the two traditional choices of male and female.
– Other people may feel more male in some situations and more female in others.
• The 23rd chromosome from each parent determines the zygote’s biological sex.
• The mother’s egg cell always contributes an X chromosome.
• In about half of conceptions, the father’s sperm cell also contributes an X chromosome, so the
zygote has XX sex chromosomes. In about half of conceptions, the father’s sperm cell
contributes a Y chromosome instead, so the zygote has XY sex chromosomes.
• Once the sex chromosomes of a zygote are determined, they further influence biological sex by
affecting what sex glands, or gonads, the zygote will eventually develop.
– Until about the sixth week of development, male and female embryos are the same,
except at the genetic level.
– Around six to seven weeks, embryos with XY sex chromosomes start to develop the male
sex glands, called testes; and embryos with XX chromosomes start to develop the female
sex glands, called ovaries.
• The Y chromosome contains a special gene that affects how the gonads develop. This gene is
called SRY, which stands for “sex determining region on the Y chromosome.”
• Female-ness is the default human biological state: the embryo will develop a female
reproductive system unless it is masculinized by hormonal action.
• These sex glands are part of the endocrine system, and they release chemicals called hormones
into the bloodstream.
• During puberty, the ovaries begin to release more of one class of sex hormones, called
estrogens.
• In males, the testes release greater amounts of another class of hormones, called
androgens.
• However, all people have estrogens and androgens, and both are crucial to proper
development.
, • As the developing human undergoes puberty, the hormones released by the sex glands cause
physical changes to occur that are referred to as secondary sex characteristics.
• Directly related to sexual reproduction
• In females, increases in estrogens cause primary sex characteristics such as the
maturation of the uterus, the vagina, and the two ovaries, including the egg cells
contained in the ovaries.
• In males, increases in androgens cause primary sex characteristics that include the
maturation of the penis and the two testes and the beginning of sperm cell production
in the testes.
• The clearest sign of primary sex characteristics in a female occurs when she experiences
menarche, the first menstrual period.
• In males, outward signs like muscle development and voice changes are more obvious,
but the most important aspect of physical development is not outwardly visible.
• This important change, the beginning of sperm cell production in the testes, is called
spermarche, and usually occurs at about age 12.
• Not directly related to sexual reproduction
• These changes start to appear in girls at about 8 years of age and in boys at about 9 or
10.
• For both sexes, this includes the development of darker and thicker body hair on the
legs, in the armpits, and in the pubic area. In addition, both sexes experience a growth
spurt.
• Females gain more fat, their waists become more defined, and their breasts develop.
• Males gain more muscle mass and develop facial hair; their voices deepen, and their
jaws become more angular.
• There are very small differences between the brains of males and females.
– However, these differences are not necessarily caused by sex difference: the social
environment also shapes how our brain develops, and males and females
experience different environments
in our society.
– Across most measures, male and
female brains are remarkably similar.
• According to the gender similarities hypothesis, males and females are similar in most
psychological processes. Some research has linked physical aggression with levels of
testosterone, and males typically have more testosterone than females
• Biological sex, the physical aspects of being male or female, is different from gender, the social
differences between being male or female.
– Most people feel that their gender matches their biological sex.
But approximately 1 percent to 3 percent of the population reports being transgender, meaning they feel
their gender is different from their biological sex
• In addition, gender can extend beyond the two traditional choices of male and female.
– Other people may feel more male in some situations and more female in others.
• The 23rd chromosome from each parent determines the zygote’s biological sex.
• The mother’s egg cell always contributes an X chromosome.
• In about half of conceptions, the father’s sperm cell also contributes an X chromosome, so the
zygote has XX sex chromosomes. In about half of conceptions, the father’s sperm cell
contributes a Y chromosome instead, so the zygote has XY sex chromosomes.
• Once the sex chromosomes of a zygote are determined, they further influence biological sex by
affecting what sex glands, or gonads, the zygote will eventually develop.
– Until about the sixth week of development, male and female embryos are the same,
except at the genetic level.
– Around six to seven weeks, embryos with XY sex chromosomes start to develop the male
sex glands, called testes; and embryos with XX chromosomes start to develop the female
sex glands, called ovaries.
• The Y chromosome contains a special gene that affects how the gonads develop. This gene is
called SRY, which stands for “sex determining region on the Y chromosome.”
• Female-ness is the default human biological state: the embryo will develop a female
reproductive system unless it is masculinized by hormonal action.
• These sex glands are part of the endocrine system, and they release chemicals called hormones
into the bloodstream.
• During puberty, the ovaries begin to release more of one class of sex hormones, called
estrogens.
• In males, the testes release greater amounts of another class of hormones, called
androgens.
• However, all people have estrogens and androgens, and both are crucial to proper
development.
, • As the developing human undergoes puberty, the hormones released by the sex glands cause
physical changes to occur that are referred to as secondary sex characteristics.
• Directly related to sexual reproduction
• In females, increases in estrogens cause primary sex characteristics such as the
maturation of the uterus, the vagina, and the two ovaries, including the egg cells
contained in the ovaries.
• In males, increases in androgens cause primary sex characteristics that include the
maturation of the penis and the two testes and the beginning of sperm cell production
in the testes.
• The clearest sign of primary sex characteristics in a female occurs when she experiences
menarche, the first menstrual period.
• In males, outward signs like muscle development and voice changes are more obvious,
but the most important aspect of physical development is not outwardly visible.
• This important change, the beginning of sperm cell production in the testes, is called
spermarche, and usually occurs at about age 12.
• Not directly related to sexual reproduction
• These changes start to appear in girls at about 8 years of age and in boys at about 9 or
10.
• For both sexes, this includes the development of darker and thicker body hair on the
legs, in the armpits, and in the pubic area. In addition, both sexes experience a growth
spurt.
• Females gain more fat, their waists become more defined, and their breasts develop.
• Males gain more muscle mass and develop facial hair; their voices deepen, and their
jaws become more angular.
• There are very small differences between the brains of males and females.
– However, these differences are not necessarily caused by sex difference: the social
environment also shapes how our brain develops, and males and females
experience different environments
in our society.
– Across most measures, male and
female brains are remarkably similar.
• According to the gender similarities hypothesis, males and females are similar in most
psychological processes. Some research has linked physical aggression with levels of
testosterone, and males typically have more testosterone than females
