Is there any example where knowing the truth about genetic causes of personality traits lead to some outcome benefiting humanity?
This example does not conform to Your specification exactly. There is a genetic disease called phenylketonuria, which, if detected early, can be managed by a strict, lifelong diet, low on aminoacid phenylalanine. This prevents mental retardation (plus health problems like seizures). So, in this particular health condition, you can affect IQ by food, and you can do that in time thanks to genetic screening of newborns. IQ is not exactly a personality trait, although we use intelligence as something to describe a psychology of a person. Still, even if the IQ is under the focus of psychology, phenylketonuria is a medical condition, there are other effects than those on intelligence.
Please, does anybody have a better example than this for Viliam ? I am really curious...
Related: The Blank Slate, The Psychological Diversity of Mankind, Admitting to Bias
"Hjernevask" a well known (in Norway at least) documentary series that I am sure will be interesting to rationalists here is now available with English subtitles online. Produced by Ole Martin Ihle and Harald Eia a Norwegian documentarian and comedian, it casts a light on both ways in which we know people to be different as well as the culture that is academia in the Nordic country and probably elsewhere as well.
The Series
The link go to the YouTube videos with English subtitles. Because linkrot sucks I'm providing another source for the videos.
Some Commentary
There was very little in the series that I found new and disagreed with some presentations. But this is not surprising given my eccentric interest in humans. (^_^) I found the interviews with the scientists and academics interesting and think that overall the series presents a good overview something well worth watching especially considering some of the debates I've seen taken place here recently. (;_;)
The latter wrote that in a 2010 article on the documentary series that I would also recommend reading. HT to iSteve where it is quoted in full.