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Lactase persistence or lactose tolerance is the continued activity of the lactase enzyme in adulthood, allowing the digestion of lactose in milk. In most mammals , the activity of the enzyme is dramatically reduced after weaning . [ 1 ]
This technology is used to add lactase to milk, thereby hydrolyzing the lactose naturally found in milk, leaving it slightly sweet but digestible by everyone. [4] Without lactase, lactose-intolerant people pass the lactose undigested to the colon [5] where bacteria break it down, creating carbon dioxide which leads to bloating and flatulence.
The majority of humans actually follow this protocol as well, and down-regulate lactase production around 3-5 years of age. Interestingly, though, the majority of caucasians, mainly those from northern european background, continue to have elevated lactase activity all the way into adulthood, and so they exhibit “lactase persistence”.
[23] [24] In areas with lactase persistence, it is believed that by domesticating animals, a source of milk became available while an adult and thus strong selection for lactase persistence could occur; [21] [25] in a Scandinavian population, the estimated selection coefficient was 0.09-0.19. [25]
The evolution of the human diet has not stopped since the end of the Paleolithic. Major functional adaptations have arisen in the last few thousand years as human technology has altered the environment. The most prevalent dietary adaptation since the Neolithic is lactase persistence, an adaptation that allows humans to digest milk. This ...
Lactose, or milk sugar, is a disaccharide composed of galactose and glucose and has the molecular formula C 12 H 22 O 11. Lactose makes up around 2–8% of milk (by mass). The name comes from lact (gen. lactis ), the Latin word for milk, plus the suffix -ose used to name sugars.
Lactase persistence [ edit ] In a 2007 study published in Nature Genetics , Tishkoff and colleagues documented three new single-nucleotide polymorphisms ( SNPs ) associated with lactase persistence (G/C-14010, T/G-13915 and C/G-13907) among ethnic groups in East Africa that differ from the allele associated with lactose tolerance that is common ...
Thus, even in the case of lactase-persistence there is a huge time delay between the onset of a new habit and the spread of the adaptive allele and so milk consumption may have been restricted to children or to lactose-reduced products. Another example of mutation positively selected by the switch to agriculture is the number of AMY1 gene copies.