Lactase persistence

[[File:Lactose Haworth.svg|thumb|right|165px|Mmm, delicious lactose!]]
{{evolution}}
'''Lactose tolerance''' is the ability to drink [[milk]] past infancy. Most [[mammal]]s can't do this,<ref name="Swallow 2003">Swallow, D. M. (2003). "Genetics of lactase persistence and lactose intolerance". Annual Review of Genetics 37: 197–219. doi:10.1146/annurev.genet.37.110801.143820. PMID 14616060</ref><ref>Cats like small amounts, but it's basically candy for them, and too much induces diarrhoea. Commercial "cat milk" has added lactase.</ref> but, in a startling example of recent [[evolution]], some populations of [[human]]s have evolved the [[beneficial mutation]] of '''lactase persistence''', the continued activity of the [[enzyme]] {{wpl|lactase}} into adulthood.

Most humans remain lactase non-persistent and hence suffer varying degrees of lactose intolerance (failure to digest milk accompanied by various undesirable gastrointestinal symptoms).<ref name="Swallow 2003"/> However, in areas where humans herd mammals, there are obvious advantages to being able to drink their copious milk. A mutation that appeared in [[Europe]] around 10,000 years ago<ref>Coelho, M., Luiselli, D., Bertorelle, G., Lopes, A. I., Seixas, S., Destro-Bisol, G. and Rocha, J. 2002. [http://www.bioquest.org/scope/projectfiles/PCR_lactase.pdf Microsatellite variation and evolution of human lactase persistence.] Human Genetics 117(4): 329–339.</ref><ref>Bersaglieri T., Sabeti P. C., Patterson N., Vanderploeg T., Schaffner S. F., Drake J. A., Rhodes M., Reich D. E. and Hirschhorn J. N. 2004. [http://genepath.med.harvard.edu/~reich/Bersaglieri.2004.pdf Genetic signatures of strong recent positive selection at the lactase gene.] American Journal of Human Genetics 74(6): 1111–20.</ref> and a mutation that appeared separately in east [[Africa]] a mere 3-6,000 years ago each allowed humans to consume milk and [[Cheese|products derived from it]] throughout their lives ([[convergent evolution]]).<ref name=wade1>[https://www.nytimes.com/2006/12/10/science/10cnd-evolve.html Study Detects Recent Instance of Human Evolution] (Nicholas Wade, ''New York Times'', 2006-12-10)</ref><ref name="Tishkoff">Tishkoff ''et al.'' [http://www.nature.com/ng/journal/v39/n1/full/ng1946.html "Convergent adaptation of human lactase persistence in Africa and Europe."] ''Nature Genetics'' '''39''', 31-40 (2007). doi:10.1038/ng1946</ref> Lactase persistence presents stronger selection pressure than any other known human [[gene]].<ref name="Troelsen_2005">{{cite journal | author = Troelsen JT | title = Adult-type hypolactasia and regulation of lactase expression | journal = Biochim. Biophys. Acta | volume = 1723 | issue = 1–3 | pages = 19–32 |date=May 2005 | pmid = 15777735}} doi:10.1016/j.bbagen.2005.02.003  </ref>

[[Creationists]] are not happy at such blatant and striking direct evidence of evolution in humans.

==Global spread==
[[File:Lactase persistence in the Old World.svg|thumb|right|165px|Distribution of lactase persistence in the Old World]]
[[File:Lactose tolerance in the Old World.svg|thumb|right|165px|Distribution of lactose tolerance in the Old World]]
Adult human populations before the [[Neolithic revolution]] were overwhelmingly lactose intolerant.<ref name="Swaminathan2007">Swaminathan, N. 2007. [http://www.scientificamerican.com/article.cfm?id=neolithic-europeans-lactose-tolerance Not Milk? Neolithic Europeans Couldn't Stomach the Stuff]. ''Scientific American''.</ref><ref name="MalmstromEtal2010">{{cite journal | author = Malmstrom H., Linderholm A., Liden K., Stora J., Molnar P., Holmlund G., Jakkobson M., Gotherstrom A. | year = 2010 | title = High frequency of lactose intolerance in a prehistoric hunter-gatherer population in northern Europe | url = | journal = BMC Evolutionary Biology | volume = 10 | issue = | page = 89}} doi:10.1186/1471-2148-10-89</ref>

The lactase persistence haplotype experienced very strong positive selection<ref name="Balter_2005">{{cite journal | author = Bersaglieri T et al.| title = Genetic Signatures of Strong Recent Positive Selection at the Lactase Gene
| journal = Am J Hum Genet | volume = 74 | issue = 6 | pages = 1111–20 |date=June 2004 | issn = | pmc=1182075 | pmid=15114531 | last2 = Sabeti
| first2 = Pardis C.
| last3 = Patterson
| first3 = Nick
| last4 = Vanderploeg
| first4 = Trisha
| last5 = Schaffner
| first5 = Steve F.
| last6 = Drake
| first6 = Jared A.
| last7 = Rhodes
| first7 = Matthew
| last8 = Reich
| first8 = David E.
| last9 = Hirschhorn
| first9 = Joel N.
}} doi:10.1086/421051</ref> during the rise of dairy farming, around 5,000 to 10,000 years ago.<ref name="Itan_2009">{{cite journal | author = Itan Y, Powell A, Beaumont MA, Burger J, Thomas MG | title = The origins of lactase persistence in Europe | journal = PLoS Comput. Biol. | volume = 5 | issue = 8 | pages = e1000491 |date=August 2009 | pmid = 19714206 | pmc = 2722739 | editor1-last = Tanaka | editor1-first = Mark M. }} doi:10.1371/journal.pcbi.1000491</ref> It can be found in 80 percent of European-descended humans. Lactase persistence also sprang up ''separately'' in [[Kenya]] around 3,000-6,000 years ago.<ref name="Tishkoff"/> It appears the mutation sprung up fairly often, but only benefited from [[natural selection]] where it was advantageous, whereas it was eliminated by [[genetic drift]] or even actively selected against elsewhere.

Correspondingly, in places with a lack of dairy farming, lactase persistence is much rarer. It is very low in southeast Asia and sub-Saharan Africa, and is absent in the Bantu of [[South Africa]] and most [[China|Chinese]] populations<ref name="Balter_2005"/> ...except amongst the nomads on the borders of China, who drank [[horse]] milk regularly (and horse milk is even higher in lactose than cow's milk). The nomads also make an [[alcohol]]ic beverage, kumis, from mare milk.

The most important factor for lactose persistence is that cow or [[goat]] herders in the middle of a steppe have only a few possible sources of food: namely, their animals and whatever sparse vegetation may be fit for human consumption. Being able to consume milk and milk products is hugely beneficial and eliminates the need to slaughter an animal for every meal which could allow for a consistent food source during the entire time the animal produces milk. However, some herding nomads have also taken to drinking blood (in addition to milk) from their animals which they gather (mostly) in non-lethal ways.

Being able to drink milk throughout life turned out to be useful. In Northern Europe milk was a good source of [[Vitamin D]], a shortage of which leads to the particularly nasty and painful disease {{wpl|Rickets|rickets|.}}<ref>{{cite journal|last1=Bersaglieri T et al.; Sabeti, Pardis C.; Patterson, Nick; Vanderploeg, Trisha; Schaffner, Steve F.; Drake, Jared A.; Rhodes, Matthew; Reich, David E.; Hirschhorn, Joel N.|title=Genetic Signatures of Strong Recent Positive Selection at the Lactase Gene|journal=American Journal of Human Genetics|date=June 2004|volume=6|issue=74|page=1114}}</ref> The 2009 British Women's Heart and Health Study reported more hip and wrist fractures, more osteoporosis and more cataracts in the lactase non-persistent group.<ref name="Smith_2009">{{cite journal | author = Smith GD, Lawlor DA, Timpson NJ, Baban J, Kiessling M, Day IN, Ebrahim S | title = Lactase persistence-related genetic variant: population substructure and health outcomes | journal = Eur. J. Hum. Genet. | volume = 17 | issue = 3 | pages = 357–67 |date=March 2009 | pmid = 18797476 | pmc = 2986166}} doi:10.1038/ejhg.2008.156</ref> They also were on average very slightly shorter (4–6mm) than the other women, as well as weighing slightly less. These were after correcting for metabolic traits, socioeconomic status, lifestyle, and fertility.

== The creationist response ==

Unsurprisingly, creationists had difficulty dealing with this incredibly blatant and powerful evidence of evolution, particularly when it hit the popular press.<ref name=wade1/><ref name=wade2>http://www.nytimes.com/2006/12/11/science/11evolve.html</ref> The standard response was to claim that this evidence for evolution is evidence ''against'' evolution, on the basis that the failure to switch off lactase is a loss of information (in the [[Information_theory#Creationist_information_theory|special creationist sense of "information"]], which is biologically meaningless).<ref name=aigsaharan/>

The other response was to claim nothing is happening and ''hey, look over there'':
* "Lactase persistence has ''nothing'' to do with molecules-to-man evolution or ape-to-human evolution or even information-adding evolution. It is just a switched-on variation within the human [[genome]]."<ref>https://answersingenesis.org/human-evolution/cavemen/does-paleo-diet-hold-evolutionary-key-good-nutrition/</ref>
* "If anything, the prevalence of lactase persistence is a testimony to the fact an [[Omniscience|all-knowing]] [[Creator]] designed the human genome with the ability to change."<ref name=aigsaharan>https://answersingenesis.org/genetics/dairy-products-early-saharan-inhabitants/</ref>
Creationists also accused scientists of [[racism]] for having dared to previously think that lactose tolerance was the normal thing and lactose intolerance the oddity,<ref>http://creation.com/lactose-intolerance</ref> [[red herring|as if that has anything to do with the question]].

[[Creation science]] research also indicates that "Rather than being an example of 'evolution in action,' [[adaptive]] mutation is an awesome witness to [[Goddidit|God’s design]] of [[bacteria]]."<ref> Georgia Purdom and Kevin Anderson. [https://answersingenesis.org/genetics/mutations/analysis-of-barry-halls-research-of-e-coli-ebg-operon/ "Analysis of Barry Hall’s Research of the E. coli ebg Operon: Understanding the Implications for Bacterial Adaptation to Adverse Environments."] Proceedings of the Sixth International Conference on Creationism, pp. 149–163 (2008)</ref> Apparently.

== Alt-right appropriation ==

The ability to consume milk and products derived from it has eventually become a part of the [[alt-right glossary]], since by omitting any mention of the East African mutation one can portray lactase persistence as an exclusive trait among the almighty White Race. A notable occurrence of this was captured on the "He Will Not Divide Us" stream in early 2017, with alt-righters downing gallons of milk (and possibly some poor soul who secretly had lactose intolerance getting diarrhoea in the process).<ref>[https://www.nytimes.com/2018/10/17/us/white-supremacists-science-dna.html Why White Supremacists Are Chugging Milk (and Why Geneticists Are Alarmed)], ''The New York Times'', 17 October 2018 (paywall)</ref>

The alt-right are less tolerant of lactose when it's in a [[Andy Ngo|milkshake]], though.

==See also==
*The false [[microevolution|microevolution vs. macroevolution]] divide that creationists love so much

==References==
{{reflist|2}}

[[Category:Evolution]]

Categories: Evolution