Sociobiological theory suggests that gender-appropriate behavior evolved to allow humanity to survive. There is evidence to support the composition of the human body; men have greater lung capacity and greater physical strength than women to better equip them to protect their family. In contrast, women are born with reproductive capabilities and are therefore biologically predetermined to care for their children, thus ensuring the survival of the human race. In 1994 Kenrick introduced the “Parental Investment Theory”. She said society is set up in such a way that women are protected and remain faithful, ensuring that men are able to pass on their genes to future generations. This also allows women to be selective in ensuring that their partner provides food, shelter, and other basic human needs. Kenrick's ideas are supported by Buss' 1994 experiment. Buss interviewed men and women in thirty-seven countries to investigate the important qualities of the opposite sex. The results showed that women prefer resourcefulness and reliability while men value chastity and youth. This study appears to support Kenrick's "parental investment theory" as Buss argues that men evolved to provide for their partners and are attracted to fertile women. Estrogen receptors in the brain are thought to cause gender-appropriate behavior. Estrogen, a hormone found in female genital tissue, acts as a ligand and, by activating estrogen receptors on the surface of brain cells, causes dramatic changes in behavior. Professors at Yale University studied the effects of estrogen and found that the hormone increases neural connectivity in the brain, resulting in more accurate memory. Turnham et al (2002) argue this because after an investigation… halfway through the paper… if you run a perfect experiment, all the evidence will be wrong as a result. You need to focus on assessing the severity of such defects. It could be argued that biosocial theory is more convincing because the many strengths of sociobiological and social learning theories combine to provide a credible explanation. This also means that the scientific facts in socio-biological theory are no longer weakened but rather strengthened by evidence supporting gender-appropriate learned behaviors. Biosocial theory allows both schools of thought to be considered equally. Overall, the Hegelian dialectical mechanism can be applied; the hypothesis, in this case the socio-biological explanation, and the antithesis, the social learning paradigm, must coexist to produce the resulting synthesis, gender-appropriate behaviors. This is how girls are born and created.