The Argument

1. The Argument

2. The Argument • Each offspring derives half its genes from its mother and half from its father (Equal Contribution of Parents)

3. The Argument • Each offspring derives half its genes from its mother and half from its father (Equal Contribution of Parents) • Each offspring / successful mating gives one ‘credit’ to a female and one ‘credit’ to a male (Equal Payoff for Parents)

4. The Argument • Each offspring derives half its genes from its mother and half from its father (Equal Contribution of Parents) • Each offspring / successful mating gives one ‘credit’ to a female and one ‘credit’ to a male (Equal Payoff for Parents) • The total success of all females is equal to the total success of all males (Equal Payoff for Sexes)

5. The Argument • Each offspring derives half its genes from its mother and half from its father (Equal Contribution of Parents) • Each offspring / successful mating gives one ‘credit’ to a female and one ‘credit’ to a male (Equal Payoff for Parents) • The total success of all females is equal to the total success of all males (Equal Payoff for Sexes) • ‘Individuals’ of the rarer sex are fitter than ‘individuals’ of the common sex (Higher Success for Rarer-Sex Individuals)

6. The Argument • Each offspring derives half its genes from its mother and half from its father (Equal Contribution of Parents) • Each offspring / successful mating gives one ‘credit’ to a female and one ‘credit’ to a male (Equal Payoff for Parents) • The total success of all females is equal to the total success of all males (Equal Payoff for Sexes) • ‘Individuals’ of the rarer sex are fitter than ‘individuals’ of the common sex (Higher Success for Rarer-Sex Individuals) • Returns from investment into rarer sex higher than from common sex (Higher Returns from Rarer Sex)

7. The Argument • Each offspring derives half its genes from its mother and half from its father (Equal Contribution of Parents) • Each offspring / successful mating gives one ‘credit’ to a female and one ‘credit’ to a male (Equal Payoff for Parents) • The total success of all females is equal to the total success of all males (Equal Payoff for Sexes) • ‘Individuals’ of the rarer sex are fitter than ‘individuals’ of the common sex (Higher Success for Rarer-Sex Individuals) • Returns from investment into rarer sex higher than from common sex (Higher Returns from Rarer Sex) • Natural selection favours individuals that invest into rarer sex (Best Investment Strategy)

8. The Argument • Each offspring derives half its genes from its mother and half from its father (Equal Contribution of Parents) • Each offspring / successful mating gives one ‘credit’ to a female and one ‘credit’ to a male (Equal Payoff for Parents) • The total success of all females is equal to the total success of all males (Equal Payoff for Sexes) • ‘Individuals’ of the rarer sex are fitter than ‘individuals’ of the common sex (Higher Success for Rarer-Sex Individuals) • Returns from investment into rarer sex higher than from common sex (Higher Returns from Rarer Sex) • Natural selection favours individuals that invest into rarer sex (Best Investment Strategy) • Natural selection neutralises perturbations from equal investment in the sexes (Convergence on Even Sex Ratio)

9. The Argument i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

10. Darwin (1871) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

11. Darwin (1871) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

12. Darwin (1871) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

13. Darwin (1871) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

14. Darwin (1871) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex Transmit the tendency to future generations vii vi Best investment strategy vii Convergence on even sex ratio

15. Darwin (1871) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex Transmit the tendency to future generations viii vi Best investment strategy vii Convergence on even sex ratio

16. Düsing (1884) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

17. Düsing (1884) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

18. Düsing (1884) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

19. Düsing (1884) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

20. Düsing (1884) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

21. Düsing (1884) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Behavioural adjustment towards equal sex ratio Best investment strategy vii ix Convergence on even sex ratio

22. Gini (1908)

23. Gini (1908) “it has all the appearance of being valid, but only the appearance”

24. Cobb (1914) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

25. Cobb (1914) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

26. Cobb (1914) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

27. Cobb (1914) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

28. Cobb (1914) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

29. Cobb (1914) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex Transmit the tendency to future generations vi viii Best investment strategy vii Convergence on even sex ratio

30. Cobb (1914) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex Transmit the tendency to future generations vi viii Best investment strategy vii Convergence on even sex ratio

31. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

32. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

33. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

34. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

35. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

36. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

37. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv Higher success of rare sex ‘individuals’ v Higher returns from rarer sex vi Best investment strategy vii Convergence on even sex ratio

38. Fisher (1930) i Equal contribution of parents ii Equal payoff for parents iii Equal payoff for sexes iv iv Higher success of rare sex ‘individuals’ v v Higher returns from rarer sex Transmit the tendency to future generations vi viii Best investment strategy vii Convergence on even sex ratio