The EVTHRB states that our brains contain evolutionary modules, including modules regarding RBs, which evolved during the EEA to enable us to survive and pass on our genes. These evolutionary modules act like schemas: filtering and processing inputs and producing outputs, including outputs for RBs. There was natural variation in these RBs, however the RBs that were adaptive and enabled us to pass on our genes were the ones that got passed on through our genes and hence over generations we became biologically predisposed to have outputs for certain RBs. These RBs were for men to be promiscuous and women to be selective. Original EVTHRB only states that we are biologically predisposed to have certain RBs, an ultimate cause, however modern EVTHRB adds that we can make cognitive decisions about our RBs based on an interaction between this ultimate cause and proximate causes e.g. our environment. The EVTHRB states that the differences between sexes in terms of RBs are a result of which RBs were adaptive in terms of sexual selection as a consequence of our anisogamy. As male sperm are mass produced and cheap, in terms of energy expenditure required to do so, it was adaptive in terms of sexual selection for male RBs to involve fertilising multiple females to maximise the likelihood of passing on their genes. Whereas because female eggs are produced in smaller numbers and are more expensive, in terms of energy expenditure required to do so, it was adaptive in terms of sexual selection for female RBs to involve choosing a male partner with good genes and the means to provide for them and their offspring to maximise the likelihood of the survival of their genes. RBs are shown in both: intra sexual selection, where members of one sex compete against each other for access to a member of the opposite sex to fertilise and pass on their genes; and inter sexual selection, where members of one sex compete to chose or be chosen by a member of the opposite sex in order to pass on their genes. The concept of intra sexual selection leading to pre copulation competition (where males compete against each other prior to copulation to gain access to a female to fertilise and pass on their genes) comes from a study by Daly and Wilson, who found a positive correlation between the ages of male same-sex homicide and the ages when men compete against each other for a female partner. This supports the above concept by implying a link between male same-sex competition (inferred from ages of male same-sex homicide) and men trying to gain access to a female to fertilise and pass on their genes, as the theory predicts. However a weakness of this study in terms of its ability to support the above theory is that the link between male same-sex competition and male same-sex homicide was inferred, hence we can’t conclude there is causality between male same-sex competition and men trying to gain access to females to fertilise and pass on their genes. Thus this study can’t be used as unequivocal support for the above theory. The concept of intra sexual selection leading to sneak copulation competition (where non-dominant males copulate with the female partner of an alpha male, without the alpha male’s knowledge, in order to pass on their genes) comes from a study by Riley, who found that in the UK 20% of children are offspring of a male other than the presumed father, which could be a result of sneak copulation competition, as the theory predicts. The concept of intra sexual selection leading to post copulation sperm competition (where male sperm compete, post copulation, within the female reproductive tract to fertilise the egg and thus pass on the male’s genes) comes from a study by Short, who compared the testes size of male chimpanzees, gorillas and humans with the respective female promiscuity levels. Short found a positive correlation between female promiscuity levels (if female promiscuity levels are higher, the female is more likely to copulate