Humans might have adapted to feel happy when they have partners, because this would result in reproduction to ensure survival, and humans might have adapted to feel unhappy when they have a poor diet, because this works negatively against the body, and hence, would be a signal for the person to remedy their state. The amygdala is required for species survival; it influences autonomic and hormonal responses through its connections to the hypothalamus. It influences our conscious awareness of the positive and negative consequences of events and objects through its connections to the prefrontal cortex. The amygdala helps us differentiate between right and wrong, especially with regards to social conduct (Kolb 435). Can this really explain, however, the myriad of feelings that humans have, reactions to the smallest detail and to major events? In the 21st century, is self-preservation still the leading cause that dictates our emotional responses? In this age, people are willing and encouraged to change their neurochemistry to better adapt to society. A person might feel sad or angry due to biological switches that were created to help the humans avoid danger, but today they are encouraged to feel "happy," or at least "un-depressed," so that they might continue their life as a productive member of society. This is accomplished many times by the use of anti-depressants. .
Antidepressants are thought to act by improving chemical transmission, especially in serotonin. A particular group of antidepressants, selective serotonin reuptake inhibitors, block the transporter so serotonin remains in the synaptic cleft for a longer period, thus prolonging its action on postsynaptic receptors (Kolb 207). Scientists are not sure how antidepressants work for some patients, and twenty percent of people fail to respond to drugs to all, or cannot tolerate the side effects of these medications.