What causes sudden behavior changes?

How much do testosterone levels differ among people of different ethnicities? What are the causes and consequences?

• Is there a meaningful difference in testosterone levels among people of different ethnicities? What are the consequences of this? Are the differing levels enough to make a meaningful difference in looks or behavior? How much? Does culture play a role if at all in causing these changes? Or is culture affected by these changes? This study talks about Pakistani men vs. europeans: http://www.ncbi.nlm.nih.gov/pubmed/12608929 Related questions:

• Answer:

  A study was done to compare testosterone levels in men from Pennsylvania, USA to those from Beijing, China. It showed that the Pennsylvanians had a higher average testosterone level than the Beijingers, but this also included Asians in Pennsylvania compared to Asians in Beijing. You can conclude from this that it's more about lifestyle than genetics. (Unfortunately the link to the study is now dead, so I'll update this if I come across it again.) There's been many studies on testosterone and diet, such as http://jap.physiology.org/content/82/1/49.full. You get some obvious stuff like "meat & eggs=more testosterone". Some folks have even conducted diet experiments, such as in http://www.artofmanliness.com/2013/01/18/how-to-increase-testosterone-naturally/ The author set out to eat as many testosterone increasing foods as he could in 90 days while maintaining a healthy and unstressful lifestyle. After all that, his testosterone levels doubled. Now with this information in hand, let's look at the Beijing/Pennsylvania comparison again. Which group is more likely to eat more meat and exercise regularly? Which group is more likely to experience greater levels of daily stress, pollution, and sleep deprivation? With that information in mind, the results are obvious.