This dissertation is a set of three studies focusing on the implications of evolutionary psychology (EP) to consumer behavior research. EP derives from the Darwinian theory of evolution and posits that just as our bodies are subject to natural and sexual selection, also our minds are adapted to their environment and, as such, we can investigate the biological basis of our behaviors. The first study is a theoretical article, focusing on the effects of hormone oxytocin (OXT) on consumer behavior. OXT has been shown to have effects on maternal care, attachment, relationships, and trust. This hormone is the focus of studies in behavioral economics, psychology and neurology, with obvious implications for consumer behavior. Previous studies on OXT have shown that oxytocin is related to our social life, i.e. related to situations with family and friends, as well as increasing our attention to the social cues in our faces (as eye gaze and smiles). Research on OXT and other hormones opens a new era of interdisciplinary studies on consumer behavior, in which researchers can incorporate psychometric measures (answered by research subjects) to biological features, as OXT, endorsing and validating findings that go beyond responses to questionnaires. It is thus possible to investigate the biological basis of consumer behavior regarding the effects of OXT on measures such as brand trust, and others. The second article is an experimental study, double-blinded, that checks the effects of OXT on brand trust. The results show that OXT is context-dependent, and it shows its most prominent results when the brand relates to social situations (friends and family). Three experiments were conducted comparing known and unknown brands, the country of origin effect and social and status brands. Known and unknown brands improved their brand trust measures when respondents were under the effect of OXT compared to placebo. Furthermore, social brands had the most pronounced effects of OXT when compared to status brands. Thus, this is first study to show positive effects of OXT on brand trust. The final study is an investigation of the post-modern epistemology to the positivist paradigm in the sex vs. gender subject. Various researchers posit that gender is as a new paradigm for our generation, in which every individual can choose his set of male and female characteristics. But when comparing the effect of biological sex vs. gender (using the Bem Sex-Role Inventory) in retaliatory behaviors in a consumer setting, only sex was able to explain the differences in behavior, not gender. Although post-modernists affirm that our biology only affects our gender as far as our genitals are concerned, differences in retaliatory behaviors are better explained by sex, not gender, corroborating the positivist epistemology.