The group studied DNA from adults who were lactose intolerant and compared them to sequences from adults who were lactose tolerant. They found that the specific mutations accounting for lactose intolerance were all in the same region of DNA (outside of the coding region btw), identical for peoples from widely ranging geographical areas. What's more, lactose intolerance (non-persistence) is more prevalent than lactose persistence. It's an obvious conclusion that that lactose intolerance is the normal, baseline condition.
You were bringing up infant lactose intolerance in the context of this study, even after I pointed out that this was an unrelated condition. In this congenital disease, the lactase enzyme is completely missing or non-functional. It has nothing to do with the recent study of adult lactose persistence.
This and the preceeding are a wealth of information not provided in the thread where this was discussed. It was stated in the thread that the search for the cause of the condition was located out of the area for the lactase gene, since no mutation had been found in that area. It was not stated that any comparison was made to any other group. The relative frequency of the lactose intolerant condition was also not mentioned. I'm not sure how these numbers from the NIH fit in.
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