It's important to think about the genetic mechanisms that may have caused this evolution among europeans. It's likely an increase in the percentage of people with the short form of the serotonin transporter gene. The short form is associated with increased neuroticism and a decreased ability to get over negative life events. On the other side, this increased fear of negativity also makes carriers more conscientious. So pretty much, low-time preference is just a fear of the future. A natural pessimism if you like which encourages these types to penny pinch and save for a rainy day.  
 
On the other hand, high time preference types seem to have an overly optimistic attitude about the future. They wear rose colored glasses and seem to underestimate the potential downside of their actions. They live in the moment and extract a lot of joy out of life, only problem is their lack of planning means that sometimes, the total pie of joy shrinks over time. 
 
Another thing to think about is how much of what we consider to be differences in intelligence is just really differences in personality preferences? THe question is, what if you have two kids with exactly the same potential, however one is low serotonin, while the other is high? Well, all else being equal, the low serotonin one will be more successful, simply due to conscientousness and fearfulness.  
 
Have you ever wondered why depression is so common among highly successful people while not so much among the poor? Weird considering that the poor definitely have more negative life experiences.