The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.     
Insulin is a hormone produced by the beta cells of the pancreatic islets of the pancreas. The pancreas produces insulin in response to the presence of high levels of glucose in the blood. Insulin stimulates cells, particularly in the liver and skeletal muscles , to absorb glucose from the blood and use it as an energy source or store it as glycogen. Insulin also stimulates adipocytes to absorb glucose to build triglycerides for energy storage. Our body produces higher levels of insulin following a meal in order to remove glucose molecules from the blood before they can reach high concentrations and become toxic to the body’s cells.
This web site is a repository of publicly available information, and is not intended to form a physician-patient relationship with any individual. The content of this website is for informational purposes only. The information presented on this web site is not intended to take the place of your personal physician’s advice and is not intended to diagnose, treat, cure or prevent any disease. Discuss this information with your own physician or healthcare provider to determine what is right for you. All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions. The information contained herein is presented in summary form only and intended to provide broad consumer understanding and knowledge. The information should not be considered complete and should not be used in place of a visit, call, consultation or advice of your physician or other health care provider. Only a qualified physician in your state can determine if you qualify for and should undertake treatment.