According to first principle of biological level of analysis, there are biological correlates of behavior. The hormone oxytocin is secreted by the hypothalamus and released into the blood stream via the pituitary gland or into the brain and spinal cord where it unites with oxytocin receptors; it mostly acts as a neurotransmitter in the brain. Oxytocin is responsible for trust between people. Experimental manipulation of this hormone has shown change in levels of trust.
According to evolutionary psychology, trust is a vital tool in the relationship between humans; also it is an adaptive mechanism meaning that disloyalty will break the bonds between individuals.
Baumgartner et al. (2008) has conducted an experimental research where he was aiming to investigate the role of oxytocin in trust in economic behavior. Participants were the economists and neuroscientists were to play a “trust” game and amongst the participants there were two groups: placebo and those who received oxytocin via nasal spray. The results were obtained through the fMRI scans whether the participant received placebo or the actual hormone. The placebo group showed less trust during the game comparing to those who received oxytocin. From this experiment, it can be evaluated that oxytocin could be the explanation to why people have the ability to restore their trust for someone and be able to forgive in the long-term relationship. Also, the brain mapping is not definite however there is still a correlation between trust and oxytocin. Although, biological psychology applies the principle of reductionism still it is too simplistic if we were to establish a direct link between trust and oxytocin.