The lactase gene has not spread through the human population as only a small percentage of the human population drinks milk as an adult. The human population is

The lactase gene has not spread through the human population as only a small percentage of the human population drinks milk as an adult. The human population is full of genes that have only partly spread through the population - it is actually a huge problem when studying human genetics since as a species we violate most of the assumptions of population genetics. Humans are actually very well adapted to walking on two legs, what we are not well adapted to is the birthing problems caused by the massive increase in brain size and the rotation of the pelvis required to accomodate walking upright. Yes I know all logs are proportional, but I thought I should be precise or else someone would ask which log ;)