Being a teenager usually means going through puberty, which is caused by increasing levels of androgens (like testosterone) in men and estrogens (like estradiol) in women in the blood. The evolutionary reason for puberty is to turn a pre-reproductive individual into a reproductively capable adult. This involves increasing social awareness, changing motivations to include activities that attract potential mates or increase social status. These changes often cause stress to previously stable social relationships. All these changes require activation and in some cases re-wiring of brain centers. Few teenagers volunteer their brains for dissection, so much detail still remains to learned.