It is obvious that boys are different from girls
and men different from women.
Indeed, we know most of the reasons for these differences.
For example,
women are made to have babies and to care for them.
So they have broad hips to allow the baby to be born easily.
They also have breasts which will produce milk for the newborn child.
And they will have a maternal instinct,
which makes them want to care for their children.
Men are different.
They are made to follow a more energetic existence,
to leave the home and to go to work.
Therefore they have a more muscular build.
They are physically stronger.
And instead of giving birth and caring for babies,
they are often better at giving birth to new ideas.
They are, in fact, usually more inventive and creative.
However, the two differing roles that the sexes have played in the past
are slowly changing.
Nowadays, more and more women are planning their families
so that they may continue their careers.
They are, in fact, becoming more ambitious.
And men are beginning to play a larger part in helping in the home
and bringing up the children.
The old ideas of male dominance are disappearing.
And nowadays the two sexes are becoming more equal,
though still remaining different.
This film is about some of these differences,
about how they develop as you grow up,
and how they become important in sexual reproduction.
By knowing more about yourselves,
it is hoped that you will be able to enjoy making love when you are ready,
and also be able to avoid making babies until you want them.
A woman who is pregnant can never tell for sure, but only guess,
whether her baby will be a boy or a girl.
There is roughly an equal chance
that it will either be a boy or a girl.
And so if she does try to guess,
she will be right as often as she is wrong.
However, as soon as it is born,
she can tell easily.
If it is a boy, he will have a small penis
and a scrotum.
This is the external male sex organ.
If it is a girl,
she will have a vulva, which is the external female sex organ.
In almost every other way, however,
newborn baby boys and girls look more or less the same.
Although inside their bodies, their reproductive organs are quite different.
Indeed, unless you know beforehand,
it is often very difficult to separate the two sexes when they are so young.
But as they grow older,
parents dress boys differently from girls.
They cut their hair in a different way,
so that the sexes can be identified more easily.
Baby girls may also have slightly softer voices,
and are often softer to the touch than baby boys.
But otherwise, apart from their sex organs,
they can still look very much alike.
The lifespan of the human animal can be divided into three stages.
These are called:
Childhood is the period of physical and mental growth from birth until puberty,
which is usually reached in the young teenager.
During childhood, the infant grows
and slowly learns to become independent of its parents.
The onset of puberty marks the beginning of adolescence.
Adolescence, the second stage of life,
is the bridge between being a child and being grown up -
that is, adult.
It is a time of extremely rapid physical and mental growth.
And it is in this first stage of adolescence, called puberty,
that obvious differences between the sexes begin to appear for the first time.
We become adult when physical growth stops,
and full sexual maturity is reached.
Mental growth, or learning, never ceases.
This goes on throughout life.
Thus during adolescence,
boys and girls change into men and women.
And sooner or later, they become capable of reproducing sexually.
Boys can then become fathers and girls mothers.
And it is the changes which take place in their bodies at puberty which make this possible.
Puberty is usually completed in the early teens.
In the girl, on average, it begins when she is 11 years old,
whereas in the boy this stage is reached a little later,
perhaps when he is about 12.
But there is no rule about this.
And some boys and girls grow up either much more quickly
or much more slowly than this.
We are now going to follow these physical changes in boys and girls,
as they grow from childhood,
through puberty into adolescence,
and then finally become adult men and women.
Although young boys and girls may behave very differently,
physically, as we have said, they are very much alike.
These similarities last throughout childhood until puberty is reached.
At the age of eight or nine years,
the only obvious difference between the two sexes are the external sex organs.
The girl has the less prominent sex organ.
It is called a vulva.
At this age, all that can be seen are the two lips, or labia.
Between them are two openings.
There is the opening of the urethra,
which passes from the bladder, where the urine is stored,
and a second opening to the vagina.
This opening may be partly closed by a piece of skin called the hymen.
In addition,
hidden between the lips of the vulva is a small organ called the clitoris.
A boy of this age will have a small penis,
and underneath it a sac called the scrotum.
The penis is used to pass urine,
and if the foreskin is pulled back,
the opening of the urethra can be seen.
This is the only opening in the male sex organ.
Inside the scrotum are two testes,
one on either side.
Some boys have their foreskins removed when they are babies.
This is called circumcision.
Other well-marked physical differences between the sexes at this age are hard to find,
though the girl may be slightly fatter and softer than a boy of the same age.
Inside the body, the reproductive organs are very different in boys and girls.
These organs are not fully developed at this age
and will not mature until puberty.
The girl has paired ovaries high in her abdomen.
The ovaries will produce her eggs, or ova, after puberty.
From near the ovaries,
pass the fallopian tubes, or oviducts,
which connect with the pear-shaped uterus, or womb,
where the baby will develop if the girl becomes pregnant.
The womb opens below through its cervix, or neck,
into the vagina.
The vagina, in turn, opens to the exterior, as we have seen,
between the lips of the vulva.
The boy has paired testes,
which instead of remaining high in the abdomen,
have descended into the scrotum.
His testes will produce spermatozoa, or sperm, after puberty.
The sperm so produced
will pass to the exterior through the epididymis
into tubes called the vas deferens.
These open into the urethra,
which open to the outside at the tip of the penis.
Opening into these tubes
are a number of glands,
in particular the seminal vesicles
and the prostate gland,
whose functions will be described later.
Both sexes have a urinary bladder
which collects urine from the kidneys
and which empties through the urethra.
In the female, the urethra conducts only urine.
But in the male,
the urethra functions to pass both urine
and sperm to the outside of the body.
The gradual process of growing up throughout childhood
becomes suddenly speeded up as puberty approaches.
Between the ages of, say, nine and 16,
physical and psychological changes begin to take place in both sexes,
changes which mark the early beginning of the adult sexual phase of life.
This is puberty.
At this time, three events take place more or less simultaneously.
Firstly, the secondary sex characteristics appear.
Secondly, the external sex organs grow.
And thirdly, the internal reproductive organs develop to maturity.
All these changes at puberty
are brought about by the secretions of the endocrine, or ductless glands.
These glands secrete substances called hormones into the blood.
And it is these hormones which stimulate sexual development at puberty.
The master gland in control is called the pituitary gland.
This is situated just under the brain.
A kind of clock in the brain switches the pituitary gland on at puberty,
say at ten or 11 in a girl,
or somewhat later, at 12, in a boy.
Secretions from this gland enter the blood,
and circulating throughout the body, switch on other glands in turn.
For example, a hormone called gonadotrophin from the pituitary,
signals the girl's ovaries to produce large amounts
of one of the female sex hormones, oestrogen.
Another gonadotrophin, from the pituitary of a boy,
likewise signals his testes
to produce the male sex hormone testosterone.
It is these two sex hormones,
oestrogen produced from the girl's ovaries
and testosterone from the boy's testes,
which are largely responsible
for the 'femaleness' and 'maleness' of a person.
A boy who has reached puberty
will notice that his penis and scrotum are growing in size.
Hair will also appear in the region of his sexual organs
and particularly in the pubic region.
This is called pubic hair.
Hair will also appear under his arms,
on his chest.
And soon he will find it necessary to shave his beard and moustache.
His voice will break,
his Adam's apple grow in size.
And he will begin to grow taller quite rapidly.
He will put on weight.
His muscles will develop in size.
He is, in fact, beginning to change into a man.
Equally striking changes will become evident in the young girl reaching puberty.
The hormones secreted by her ovaries
will stimulate the lips of her vulva and her clitoris to grow.
Hair will also develop in her pubic region
and also under her arms.
Her breasts will begin to grow
and her body, instead of becoming muscular,
will take on the rounded contours of the female form.
She will develop a narrow waist.
Her hips will broaden,
and she too will grow rapidly in height.
Soon she will be recognisable as a young woman.
The internal reproductive organs also grow and mature at puberty,
so that by the age of 14 or 15,
most boys and girls are reproductively fertile,
and capable of becoming parents.
In the boy, the hormones stimulate the growth of the testes,
which will begin to produce living, mobile spermatozoa
from the numerous coiled seminiferous tubules
within the testes.
These sperm will pass to the exterior
through the epididymis,
the vas deferens and finally the urethra.
Semen, the milky fluid in which
the sperm are ejaculated to the outside,
is produced by the prostate gland
and the seminal vesicles.
In the girl, her hormones stimulate her ovaries,
fallopian tubes, uterus and vagina
to grow in size until they are mature.
Then her menstrual cycles will begin.
Once a month, her ovaries will release an ovum
and alternating with this, about a fortnight later,
she will have some bleeding from her vulva.
This is her monthly period,
and is called menstruation.
It is a sign that she is reproductively mature
and capable of having a baby.
Puberty is said to be at an end
when both sexes are capable of reproducing.
That is, the boy is able to produce sperm
and the girl ova.
Apart from the physical changes which take place at puberty,
the sex hormones also bring about changes in the behaviour of adolescent boys and girls.
With an increasing frequency,
boys will begin to notice girls,
and girls, likewise, become interested in boys.
They will be attracted to one another,
both physically, so that they will want to kiss and neck,
and emotionally, so that they simply want to be together and talk.
They have a mutual need for each other,
and this need represents the beginning of love between the two sexes.
Early in adolescence,
a boy will notice that he can become sexually excited.
His penis will become erect,
and if he masturbates, by moving the skin on his penis up and down,
semen containing many million of his sperm
will be ejaculated to the exterior from the end of his penis.
At this moment,
he will experience a very pleasurable sensation called orgasm.
Masturbation is important to development,
and may provide a natural and healthy sexual outlet
for adolescent boys for several years.
Similarly, a young girl may also become sexually excited.
She will then notice that her vulva becomes moist,
and if she masturbates by moving her hand over the lips of her vulva,
or stimulates her clitoris or vagina,
she too may have this pleasurable sensation called orgasm.
As in the boy,
masturbation in the girl is quite normal
and also plays an important part in her development.
Adolescence ends when physical growth is complete
and full sexual maturity is achieved.
The age at which this may be reached varies considerably.
It may be as early as 15 years,
or as late as 20 years.
The differences already described which separate the adolescent boy and girl
are naturally much more strongly accentuated in the adult.
The primary sex characteristics,
that is the sex organs,
are now fully developed.
In the male, the penis and scrotum are mature,
and pubic and genital hair are present.
In the female, the vulva is also fully grown,
though often partly concealed by hair.
The secondary sexual characteristics are also now fully formed in both sexes.
In the adult male,
underarm, facial and body hair are present,
but vary in their abundance from person to person.
The voice is now completely broken,
and characteristically deeper than that of a woman.
In general, the adult male will be larger and more muscular than the adult female.
But, of course, there are exceptions to this rule.
No particular body build can be said to be normal.
All that can be stressed is that there exists a range of normals.
In the adult female, the breasts are now fully developed,
although again, these will vary in size and shape from person to person.
The growth of her body hair is restricted to under her arms and on her vulva.
And her characteristic smoothly round female form
is brought about by deposits of body fat.
Typically, she has a narrow waist,
broader hips,
and generally will be smaller than the average male.
Men find women attractive to look at
and become sexually aroused by seeing, for example,
their breasts and vulvas.
To a lesser extent,
a naked man's body may also arouse a woman sexually.
Thus, quite apart from the obvious biological use of breasts in a woman to provide milk
and the normally heavier musculature of the male
to endow him with additional physical strength,
these features will also have a sex appeal.
As a result of necking and petting,
both the boy and girl may become sexually excited.
And if the circumstances are right,
sexual intercourse may follow.
His penis will become stiff and erect,
and her vulva moist, as a result of the secretions from the walls of the vagina.
So that when the penis is placed between the lips of the vulva,
penetration into the vagina will take place.
This may be difficult sometimes,
particularly if the girl is not fully aroused,
or if she is feeling guilty
or perhaps if it is her first intercourse.
Normally, however, the vagina expands to take the erect penis,
however large it may be.
After a number of pelvic movements, or thrusts,
orgasm may be achieved by both sexes.
At the time of orgasm in the male,
many millions of his sperm will be ejaculated high in the vagina.
And if these sperm swim up through the uterus
into the fallopian tubes to meet the ovum,
fertilisation may take place,
and the girl may become pregnant.
Boys and girls often have sexual intercourse long before they are ready to have babies.
There is nothing wrong with this,
and many people believe that sexual experience in adolescence
is essential for normal development.
However, unless the girl is taking the contraceptive or birth pill,
or the boy always uses a sheath,
she is very likely to become pregnant.
Unmarried teenagers don't make the best parents.
It is neither fair on yourselves, nor your child,
that you should become parents so young.
But making love is important to a lot of young people.
So be prepared.
Never make love without taking precautions.