Reproduction among humans usually occurs with penile-vaginal
penetration.[81]
Male orgasm usually includes ejaculation, a
series of muscular contractions
that deliver semen containing male
gametes known as sperm cells or
spermatozoa from the penis into the vagina. The subsequent route of
the sperm from the vault of the vagina is through the cervix and into the
uterus, and then into the
fallopian tubes.
Millions of sperm are present in each ejaculation, to increase the
chances of one fertilizing an egg or ovum (see sperm
competition). When a fertile ovum from the female is present in
the fallopian tubes, the male gamete joins with the ovum, resulting
in fertilization and
the formation of a new embryo. When a fertilized
ovum reaches the uterus, it becomes implanted in the lining of the
uterus – known as the endometrium – and a
pregnancy
begins.[81]
Unlike most species, human sexual activity is not linked to periods
of estrus and can
take place at any time during the reproductive cycle, even during
pregnancy.[82]
Where a sperm donor
has sexual intercourse with a woman who is not his partner, for the
sole purpose of impregnating the woman, this may be known as
natural insemination, as
opposed to artificial
insemination. However, most sperm donors donate their sperm
through a sperm bank and
pregnancy is achieved through artificial insemination.[83]
In 2005, the World
Health Organization (WHO) estimated that 123 million women
become pregnant world-wide each year, and around 87 million of
those pregnancies or 70.7% are unintentional. About 46 million
pregnancies per year reportedly end in induced abortion.[84]
About 6 million U.S. women become pregnant per year. Out of known
pregnancies, two-thirds result in live births and roughly 25% in
abortions; the remainder end in miscarriage. However, many more
women become pregnant and miscarry without even realizing it,
instead mistaking the miscarriage for an unusually heavy menstruation.[85]
The U.S. teenage
pregnancy rate fell by 27 percent between 1990 and 2000, from
116.3 pregnancies per 1,000 girls aged 15–19 to 84.5. This data
includes live births, abortions, and fetal losses. Almost 1 million
American teenage women, 10% of all women aged 15–19 and 19% of
those who report having had intercourse, become pregnant each
year.[86]
Britain has been stated to have a teenage pregnancy rate similar to
America's.[87]
Alex Comfort and
others posit three potential advantages of intercourse in humans,
which are not mutually exclusive: reproductive, relational, and
recreational.[8][124]
While the development of the
Pill and other highly effective forms of contraception in the mid- and late 20th century increased
people's ability to segregate these three functions, they still
overlap a great deal and in complex patterns. For example: A
fertile couple may have intercourse while contracepting not only to
experience sexual pleasure (recreational), but also as a means of
emotional intimacy (relational), thus deepening their bonding,
making their relationship more stable and more capable of
sustaining children in the future (deferred reproductive). This
same couple may emphasize different aspects of intercourse on
different occasions, being playful during one episode of
intercourse (recreational), experiencing deep emotional connection
on another occasion (relational), and later, after discontinuing
contraception, seeking to achieve pregnancy (reproductive, or more
likely reproductive and relational).[124]
Nearly all Americans marry during their lifetime; yet close to
half of all first marriages are expected to end in separation or
divorce, many within a few years,[125]
and subsequent marriages are even more likely to end.[126]
Sexual dissatisfaction is associated with increased risk of divorce
and relationship dissolution.[126]
According to the
National Survey of Sexual Health and Behavior (NSSHB), in 2010,
men whose most recent sexual encounter was with a relationship
partner reported greater arousal, greater pleasure, fewer problems
with erectile function, orgasm, and less pain
during the event than men whose last sexual encounter was with a
non-relationship partner.[101]
According to the Journal of Counseling & Development,
many women express that their most satisfying sexual experiences
entail being connected to someone, rather than solely basing
satisfaction on orgasm.[127]
With regard to adolescent
sexuality, sexual intercourse is often for relational and
recreational purposes as well. However, teenage
pregnancy is usually disparaged, and research suggests that the
earlier onset of
puberty for children puts pressure on children and teenagers to
act like adults before they are emotionally or cognitively
ready,[128][129]
and thus are at risk to suffer from emotional distress as a result of their sexual
activities.[129][130][131][132][133]
Some studies have concluded that engaging in sex leaves
adolescents, and especially girls, with higher levels of stress and
depression.[134]
A majority of adolescents in the United States have
been provided with some information regarding sexuality,[135]
though there have been efforts among social conservatives in the
United States government to limit sex education in
public schools to abstinence-only
sex education curricula.[136]
One group of Canadian researchers
found a relationship between self-esteem and sexual activity. They
found that students, especially girls, who were verbally abused by
teachers or rejected by their peers were more likely than other
students to engage in sex by the end of the Grade 7. The
researchers speculate that low self-esteem increases the likelihood
of sexual activity: "low self-esteem seemed to explain the link
between peer rejection and early sex. Girls with a poor self-image
may see sex as a way to become 'popular', according to the
researchers".[137]
In India, there is growing
evidence that adolescents are becoming more sexually active outside
of marriage, which is feared to lead to an increase in the spread
of HIV/AIDS among
adolescents, as well as the number of unwanted pregnancies and
abortions, and add to
the conflict between contemporary social values. In India,
adolescents have relatively poor access to health care and
education, and with cultural norms opposing extramarital sexual
behavior, "these implications may acquire threatening dimensions
for the society and the nation".[138]
Not all views on adolescent sexual behavior are negative,
however. Psychiatrist Lynn Ponton writes,
"All adolescents have sex lives, whether they are sexually active
with others, with themselves, or seemingly not at all," and that
viewing adolescent sexuality as a potentially positive experience,
rather than as something inherently dangerous, may help young
people develop healthier patterns and make more positive choices
regarding sex.[128]
Likewise, others state that long-term romantic relationships allow
adolescents to gain the skills necessary for high-quality
relationships later in life[139]
and develop feelings of self-worth. Overall, positive romantic
relationships among adolescents can result in long-term benefits.
High-quality romantic relationships are associated with higher
commitment in early adulthood[140]
and are positively associated with self-esteem, self-confidence,
and social competence.[141][142]