Lactase Persistence

Lactase persistence is the ability of adult humans to digest lactose. This ability has its origins in different parts of the world (which occurred through convergent evolution) such as Central and Northern Europe, West Africa, the Middle East and western India.

Genetic changes allowing for lactase persistence started to spread quickly after the introduction of milkable domestic animals, especially in Northern Europe about 8,000 years ago. (1)Colledge S, Conolly J, Dobney K, Manning K, Shennan S. Origins and Spread of Domestic Animals in Southwest Asia and Europe (Univ Col London Inst Arch Pub) (UCL Institute of Archaeology Publications). Left Coast Press (July 15, 2013). Available here. (3)Leonardi M, Gerbault P, Thomas MG, Burger J. The evolution of lactase persistence in Europe. A synthesis of archaeological and genetic evidence. Volume 22, Issue 2, February 2012, Pages 88–97. Available here.

Historically, before the development of agriculture and the domestication of animals milk was only available from the lactating mothers. Its supply stopped after the weaning period.
With a sudden change in diet from breastfeeding through weaning, specifically because of the absence of milk, lactase was not required anymore and so its production by the body was drastically reduced.

Around 8000 years ago, Europe started domesticating milk-producing animals, allowing the consumption of milk on a regular basis. The trend spread to the Middle East and West India. (2)Itan Y, Jones BL, Ingram CJ, Swallow DM, Thomas MG. A worldwide correlation of lactase persistence phenotype and genotypes. BMC Evolutionary Biology 2010, 10:36. Available here.

In Africa, especially in the countries south of the Sahara, lactose persistence most likely originated thanks to the domestication of the camel. (4)Enattah NS, Jensen TG, Nielsen M, Lewinski R, Kuokkanen M, Rasinpera H, et al. Independent Introduction of Two Lactase-Persistence Alleles into Human Populations Reflects Different History of Adaptation to Milk Culture. Am J Hum Genet. Jan 10, 2008; 82(1): 57–72. Available here.

Consistent milk consumption existed in these locations for about 8,000 years which allowed for the genetic mutation to occur resulting in lactase persistence.

To visualize the centers of lactose persistence or see where lactose intolerance is most prevalent, see the following map. Red color represents the most lactose tolerant populations, while blue represents a high percentage of lactose intolerance. The further from the centers, the more lactose intolerant the populations are. (5)Itan Y, Jones BL, Ingram CJ, Swallow DM, Thomas MG. Interpolated map of Old World LP phenotype frequencies. Itan et al. BMC Evolutionary Biology 2010 10:36. Available here.

Lactase persistance map

References   [ + ]

1. Colledge S, Conolly J, Dobney K, Manning K, Shennan S. Origins and Spread of Domestic Animals in Southwest Asia and Europe (Univ Col London Inst Arch Pub) (UCL Institute of Archaeology Publications). Left Coast Press (July 15, 2013). Available here.
2. Itan Y, Jones BL, Ingram CJ, Swallow DM, Thomas MG. A worldwide correlation of lactase persistence phenotype and genotypes. BMC Evolutionary Biology 2010, 10:36. Available here.
3. Leonardi M, Gerbault P, Thomas MG, Burger J. The evolution of lactase persistence in Europe. A synthesis of archaeological and genetic evidence. Volume 22, Issue 2, February 2012, Pages 88–97. Available here.
4. Enattah NS, Jensen TG, Nielsen M, Lewinski R, Kuokkanen M, Rasinpera H, et al. Independent Introduction of Two Lactase-Persistence Alleles into Human Populations Reflects Different History of Adaptation to Milk Culture. Am J Hum Genet. Jan 10, 2008; 82(1): 57–72. Available here.
5. Itan Y, Jones BL, Ingram CJ, Swallow DM, Thomas MG. Interpolated map of Old World LP phenotype frequencies. Itan et al. BMC Evolutionary Biology 2010 10:36. Available here.

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