How do animals reproduce?

• 25.1 Reproductive options (and ethical issues) are on the rise.
• 25.2 There are costs and benefits to having a partner: sexual versus asexual reproduction.
• 25.3 Fertilization can occur inside or outside a female’s body.

Male and female reproductive systems have important similarities and differences.

• 25.4 Sperm are made in the testes.
• 25.5 There is unseen conflict among sperm cells.
• 25.6 This is how we do it: Can males increase sperm investment in response to the presence of another male?
• 25.7 Eggs are made in the ovaries (and the process can take decades).
• 25.8 Hormones direct the process of ovulation and the preparation for gestation.

Sex can lead to fertilization, but it can also spread sexually transmitted diseases.

• 25.9 In fertilization, two cells become one.
• 25.10 Numerous strategies can help prevent fertilization.
• 25.11 Sexually transmitted diseases reveal battles between microbes and humans.

Human development occurs in specific stages.

• 25.12 Early embryonic development occurs during cleavage, gastrulation, and neurulation.
• 25.13 How does an embryo become male or female?
• 25.14 There are three stages of pregnancy.
• 25.15 Pregnancy culminates in childbirth and the start of lactation.

Reproductive technology has benefits and dangers.

• 25.16 Assisted reproductive technologies are promising and perilous.