An adult's ability to produce the lactase enzyme is determined almost entirely by his or her genes. Because of this, simply knowing your genotype is almost enough to know whether you continue to produce the lactase enzyme. However, whether you are actually lactose tolerant or intolerant can depend on non-genetic factors, such as the composition of your gut bacteria. And as with many traits, how lactose intolerant you are depends on your individual circumstances—you might have different outcomes from someone else with the same genotype.

For healthy individuals with secondary lactose intolerance, it may be possible in some cases for the bacteria in the large intestine to adapt to an altered diet and break down small quantities of lactose more effectively‏⁵¹ by habitually consuming small amounts of dairy products several times a day over a period of time. This is not suitable for people who have an underlying or chronic illness which may have damaged the intestinal tract in a way which prevents the lactase enzyme from being expressed.
Some studies indicate that environmental factors—more specifically, the consumption of lactose—may "play a more important role than genetic factors in the etio-pathogenesis of milk intolerance",.‏⁵²

You keep using that article. I do not think it means what you think it means.
https://www.youtube.com/watch?v=YIP6EwqMEoE

http://www.nature.com/news/archaeology-the-milk-revo...
"Young children almost universally produce lactase and can digest the lactose in their mother's milk. But as they mature, most switch off the lactase gene. Only 35% of the human population can digest lactose beyond the age of about seven or eight (ref. 2)."

Besides examining the genes responsible for previously identified diseases, Bray and colleagues went on to look for other regions of the Ashkenazi Jewish genome that display signs of selection, in comparison to European genomes. The two strongest differences between the Ashkenazi and European populations were on chromosome 2 and 12. A region including the lactase gene, which confers lactose tolerance, on chromosome 2 showed signs of strong selection in Europeans but not the Ashkenazi.

“A variant of the lactase gene swept through Europe at around the same time as the domestication of cattle several thousand years ago,” Bray says. “This result suggests the selection preceded the European establishment of the Ashkenazi Jewish population, which is consistent with the historical record.”