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When did adult humans start drinking milk?

  1. Aug 18, 2011 #1
    Humans are the only mammal that drinks the milk of other mammals and the only mammal that drinks milk as adults. When did we start doing this?
     
  2. jcsd
  3. Aug 18, 2011 #2

    Ryan_m_b

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    Being able to drink milk after young childhood is a phenomenon called lactase persistence and has evolved multiple times in human history. Lactase persistence is caused by a mutation in the LCT (lactase) gene, the first to be discovered and the most common amongst Europeans is the -13910*T SNP whereby a cytosine is exchanged for a thymine, this mutation occurs 13.9kb upstream and is almost ubiquitously found in European populations. Other SNPs include -14010*C (common in East Africans) and -13915*G (common in Middle Eastern/North Africans). The exact method by which each SNP confers lactase persistence is unknown however it is suspected that the overlap of SNPs and transcription factor binding sites are the cause. In the case of the -13910*C it has been shown that the Oct-1 transcription factor for lactase binds more strongly with a thymine in place of a cytosine.

    Analysis of the LCT persistent gene has revealed that the sequence surrounding the gene has extensive homozygosity with diversity in this sequence is very low indicating that the genotype is advantageous and must have spread to such a high frequency recently. Attempts to date the -13910*T allele by examining microsatellite diversity date the mutation at somewhere between 7,400 and 12,000 years old. This is interesting because it coincides with the adoption of cattle farming in Europe, additionally analysis of ancient DNA shows that the allele is either not present or is at very low frequency before this time. -13915*G an SNP found in Arab genomes is dated at just 4000 years ago, 2000 years after the start of camel milk farming. It is difficult to say how lactase persistence is an advantageous allele. The calcium assimilation hypothesis that posits that in populations with insufficient sunlight lactase persistence makes up for vitamin D loss though this theory does not explain how African and Arab populations evolved LP. The nutritional hypothesis posits that the nutritional benefit gained from lactose is such an advantage on its own it is strongly selected for though there is no strong evidence of this.

    Whilst the exact reason as to why LP is an advantage is not known it is safe to say that it is clearly an advantage to have been selected for at multiple times in history.
     
    Last edited: Aug 18, 2011
  4. Aug 19, 2011 #3

    lisab

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    Very interesting and informative.

    Do you know if drinking milk introduced any new diseases to humans?
     
  5. Aug 19, 2011 #4
    There are some studies which suggest a possible link between milk and diabetes.
     
  6. Aug 19, 2011 #5

    Ryan_m_b

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    Thankyou :smile: I don't know of any specific examples I guess but drinking milk would have increased the risk of catching disease from other animals.
    Do you have any refs for this?
     
  7. Aug 19, 2011 #6

    Evo

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    They aren't considered reliable or conclusive studies.

    http://www.ncbi.nlm.nih.gov/pubmed/10426365
     
  8. Aug 19, 2011 #7

    Evo

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    Milk is pasteurized to kill pathogens in raw milk.

    http://en.wikipedia.org/wiki/United_States_raw_milk_debate#Pasteurization
     
  9. Aug 19, 2011 #8

    Ryan_m_b

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  10. Aug 19, 2011 #9

    Evo

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    Probably because it seemed too obvious. :smile: lisab was probably also thinking of disease above and beyond these illnesses, but thought I'd post them anyway.
     
    Last edited: Aug 19, 2011
  11. Aug 19, 2011 #10
    Well, http://www.time.com/time/magazine/article/0,9171,976188,00.html" [Broken] Time article references New England Journal of Medicine, which I don't have access to so can't verify it.

    http://children.webmd.com/news/20080501/new-clue-to-milk-and-diabetes-link" [Broken] article also doesn't list the source.

    T Colin Campbell, author of The CHina Study, and Caldwell Esselstyn of the Cleveland Clinic have also suggested this possible link (OK, they say there is a link, to be fair).

    However, I said "suggest a possible link" - I never said they were conclusive Evo.
     
    Last edited by a moderator: May 5, 2017
  12. Aug 19, 2011 #11

    lisab

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    Well, when the mutation evolved and humans started adding milk to their regular diets, there was no pasteurization of course. I was trying to get a rough idea of the balance of gain (calories, protein, calcium, etc.) vs. risk (pathogens) that came with becoming milk drinkers. (Certainly there must be a biological term for that balance but I've not had enough biology to know it :redface:.)
     
  13. Aug 19, 2011 #12
    What I want to know is, what made the first person who found some really old, smelly, hardened milk somewhere, that seemed completely rotten, decide to try it, and then call it cheese?

    Sort of like the first person who tried blowfish - you'd think after a few people died, folks would have decided it wasn't worth trying to find "the good parts".
     
  14. Aug 19, 2011 #13

    Evo

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    That was from 1992 and said further studies should be ready in 5-10 years, so I looked for those newer studies and found the journal link from 1999.

    Oh no, I was just saying that the aticle says they weren't conclusive, not you.
     
    Last edited by a moderator: May 5, 2017
  15. Aug 20, 2011 #14
    speaking of diseases, people used to (still?) get cowpox from milking cows.
    http://en.wikipedia.org/wiki/Cowpox

    but you could even consider that a sort of additional benefit.
     
  16. Aug 20, 2011 #15

    Ryan_m_b

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    Taken from that wiki page

    You're right of course that this would be an advantage. Catching and dealing with cowpox was such a great advantage that it was one of the things that inspired Jenner to test inoculation.
     
  17. Aug 20, 2011 #16
    huh, well i didn't even catch that. now i'm thinking all sorts of things, like cats licking milk from a dripping udder to infect cows. and the idea that smallpox may not be eliminated, but still surviving somewhere in an unknown host.
     
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