The Argument The Argument i Each offspring derives

The Argument

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

The Argument (i) (ii) 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 Argument (i) (iii) 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)

The Argument (i) (iii) (iv) 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)

The Argument (i) (iii) (iv) (v) 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)

The Argument (i) (iii) (iv) (vi) 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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Gini (1908)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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