Part 2 — Introductory material

Recapitulation of facts established—Reversal of sex attributes—Courting females and nursing males among certain birds—Attempt at explanation—Are sex-hunger and parental affection in conflict—A high standard of family life among birds—Few birds who are bad fathers—Examples of varying division of family work—A few birds who are bad parents—Where the mother takes sole charge of the eggs the father as a rule takes little interest in the family—The polygamous gallinaceous birds—Conduct affected by habits of the home—The Adélie penguins—Their co-operative child-rearing—The great emperor penguin—Scrimmage of childless mothers and fathers for possession of chickens.