High testosterone levels lead to dominant behaviour, aggression and generally a fixation with power and getting pussy. Cooperation and quietly working on things with others certainly takes a back seat then. It's individual success in terms of mating and dominating over success that is actually useful in the long run and with "boring" things.
That said, not being surprised in no evidence. In best /. fashion I haven't read the fine article, but I would want to see some mechanism that actually LEAD to lower testosterone levels. Evolution? Maybe, seems a bit short, but these are time frames that indeed were long enough to lead to lactose-tolerance to dominate in dairy-eating populations all over the world, so I wouldn't count out evolution rearing its head here. Mutations that supported drinking milk and eating cheese quickly dominated. Maybe other mutations that supported being more peaceful, not getting into pointless fights, and getting things done in a goal-oriented way instead of being fixated onto telling others what to do while holding on to five women without actually knowing what to do except fucking a lot also dominated for very good reasons.
And really: The lone fact that a LOT of people are totally capable to live their lives in dense populations without really fighting others all the time gives some weight to that. Maybe high testosterone levels are just incompatible with population growth and dense populations. Maybe they cause too much trouble to be successful (in an evolutionary sense) when all is said and done. Maybe the quietly working type of guys who are happy with one women and want to be left alone and leave others alone may be not as successful as the dominant asshole individually but there may be just much more of them and they don't get killed as often and raise more children altogether. Maybe even the fact that spraying your genes around isn't of much help when you can't support 10 women and their offspring and single women aren't that good in supporting their children plays a role here.
Every Genghis Khan may have fucked a lot, but he also will have killed a lot of men willing to fight and all the while those men who just got the bread home every day and just fucked one women were breading like rabbits and actually helped their children to prosper when you sum it up. Evolution isn't about individuals but about numbers of individuals actually surviving until maturity (and beyond, since a newborn child alone isn't going to survive for very long).