Introduction to Sex (01:40)

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Sex is at the core of the deepest human relationships. Science has only recently begun to unravel the secrets of sex.

Data on Sexual Behavior (04:32)

Dr. Alfred Kinsey was the first to approach sex in a systematic and scientific way. He asked his students to share their own experiences.

Rules of Attraction (02:03)

The role of female hormones in sexual desirability is being investigated. An unusual experiment involves tracking data about the earnings and menstrual cycle of strippers.

Physiology of Sex (03:03)

In 1958 scientists William Masters and Virginia Johnson recorded volunteers having sex and masturbating.

Images of Coitus (03:42)

Reproductive physiologist Dr. Roy Levin uses an FMRI scanner to observe a couple having sex. A cross-section shows the penis change shape during intercourse.

Addressing Male Sexual Dysfunction (02:18)

Geddings Osbon invented a practical, mechanical solution for his own impotence. His vacuum pump drew blood into the spongy erectile tissue in the penis.

Viagra (03:32)

In the 1990s, scientists at Pfizer unintentionally created a chemical compound that caused erections by relaxing blood vessels.

HIV/AIDS (03:12)

A new sexually transmitted disease was discovered in the 1980s. Gay men and intravenous drug users became infected with diseases that did not affect other people.

Sexually Transmitted Disease Prevention (05:10)

AIDS has killed more than 30 million people. Infection trends in African tribes led to the knowledge that circumcision reduces the risk of HIV infection by removing Langerhans cells.

Gender Identity (04:28)

The argument over nature versus nurture has focused on the story of Bruce/David Reimer whose penis was burned during circumcision. Dr. John Money was a leading advocate of sex change operations.

Failed Experiment in Gender Neutrality (02:20)

Reimer recalls his experience being raised as a girl after a botched circumcision. Dr. Money assured his mother that it would work. Reimer's twin brother died from a drug overdose.

Sexually Dimorphic Nucleus (02:25)

A team from the University of California discovered a structural difference in the brains of male and female rats.

Foundation of Birth Control Pill (04:49)

Scientists needed a source of progesterone to create a contraceptive pill for women. Dr. Russel Marker successfully synthesized the hormone from yams.

In Vitro Fertilization (02:01)

The first "test tube" baby was born in 1978. IVF remains stigmatized because of the option to alter genetic traits.

Designer Babies (06:00)

Scientists can use pre-implantation genetic diagnosis to screen embryos outside the womb to select those that carry healthy genes. A woman shares her personal story.

Credits: Sex. A Horizon Guide (00:38)

Credits: Sex. A Horizon Guide