Ever since life has been around, the ultimate goal has been to perpetuate life by reproduction. This goal is at the root of all life and comes as a natural instinct. From bacteria replicating in a host to tropical birds singing to potential mates, different forms of life are constantly trying to continue their lineage. Without this instinctual desire, life would be very different than how we see it today. Along with this need to reproduce, is the want to reproduce with a mate with the best genes as possible. The best way for an organism to preserve their species would be with a mate who has strong genes that will produce healthy offspring. But how could humans, for example, tell if a potential mate has genes that will help them produce healthy offspring? Recently, studies have shown that humans may make this judgement of gene state by the facial beauty of members of the opposite sex.
To determine if the recognition of facial beauty actually had something to do with the potential of the opposite person to be a good mate, researchers took heterosexual males and showed them images of average or beautiful faces of men and women. They used images of both men and women so they would be able to distinguish which area of the brain became active due to just the aesthetically pleasing makeup of the face, heterosexual men looking at other men, and which areas became active due to what the researchers called "rewarding beauty", heterosexual men looking at beautiful women. This rewarding beauty is described as the aesthetically pleasing face of a potential mate, i.e. women in the case of heterosexual men. The results of these studies, based on fMRI images of the brain, showed that there was a specific region that was active during recognition of rewarding beauty but not aesthetic beauty. This region was the sublenticular extended amygdala (SLEA). This lack of activity in the sublenticular extended amygdala leads the researchers to think that perhaps this area helps humans determine if a member of the opposite sex has desirable genes that could propagate the human species. From here, the researchers created a pathway of how they thought that a human processed this information. They categorized the observing of the various aspects of the face as the "core system" and saw that much of the activity took place in the superior temporal sulcus. The next step seemed to be a "beauty appraisal," or the step where the brain decides if the face is in the rewarding beauty category or aesthetic beauty. Depending on which direction the beauty appraisal step went seemed to show a different pathway in the brain.
These results seem to modernize the age old instinctual desire to procreate with another who has an advantageous genetic makeup and give us a present day example of why humans tend to prefer mates that are more beautiful. If nothing else, these results allow us to blame our prolonged stares at an attractive individual on our sublenticular extended amygdala.