The actual article you cite gives a more complete explanation, which is that that evolutionary pressure was based on Vitamin D. Dark pigmented skin does not absorb UV light effectively, so at high latitudes with relatively low sunlight levels, dark skinned, lactose intolerant people would suffer vitamin D deficiency. They would not know this, of course, but they would fail to thrive and die off. The lighter skinned people who carried a mutation for digesting lactose were able to absorb more UV light for endogenous vitamin D synthesis and consume milk that contained vitamin D, thus faring better farther north.

Evolution is about survival and reproduction, whether it be surviving environmental conditions, pathogens, and warfare, to name a few. With humans, it seems to have come in spurts. As technology advances and the environment changes, we probably can expect more evolutionary spurts. Of course, these are always associated with massive disruptions of the status quo.