Dr Bondar explains that until approximately 500 million years ago sex was a 'mere trickle of DNA', a thoughtless merging of cells. With the evolution of sexual organs as we know them, social hierarchies have also developed, dictated by the sexual dynamics between creatures of each species. She examines the mechanics of sexual intercourse between certain animals, describing differing tactics of seduction, from 'coercion' to 'titillation', showing images of different penises, and comparing the cost of reproductive cells in females (high) and males (low). She examines the violent methods used by some animals to inseminate females, from the bed-bug's spiked, barbed penis to the 'ballistic' spiral-shaped penis of the duck. She then explores the probability that other animals experience pleasure from sex, based on observation of their behaviour related to choosing a mate based on penis-size or other pleasure-inducing appendages. Finally, Dr Bondar describes matriarchal animal societies, noting that when the female has the reproductive power, or 'penis power', she also possesses social dominance in the group.

Dr Bondar reiterates that sex in the animal kingdom determines how males and females relate to each other, and how their population will develop. Of course, this extends to our own society as well, and her vividly written and scrupulously researched book encourages us all to think about sex - if not more frequently, then certainly more profoundly.