Possible Cause of Lactose Tolerance: Famine and Disease
Lactose intolerance is a common condition that many of us may have or know someone who
has it. It’s the inability to digest lactose in dairy, resulting in symptoms such as bloating,
stomach cramps, gas, and diarrhea. Many people have this notion that those who are lactose
intolerant have a mutation that prevents them from digesting lactose, but in reality, it’s just the
opposite. All mammals have the ability to digest lactose soon after birth because they are
receiving milk from their mothers, also known as weaning. This is due to a gene in our DNA that
is responsible for producing the lactase enzyme, which is necessary for breaking down lactose.
However, once mammals reach a certain age and no longer need to receive nutrients from their
mother’s milk, the lactase gene is repressed, and lactase production stops. Naturally like other
mammals, humans are supposed to be lactose intolerant because lactose is only needed when
we are infants. However, a mutation occurred thousands of years ago in ancient Europeans that
caused lactase persistence into adulthood.
There is some debate as to how some humans evolved to have lactase persistence. One
argument is seen in the article “Famine and Disease may have driven Ancient Europeans’
Lactose Tolerance”. Simply drinking milk consistently and experiencing its uncomfortable
symptoms was not enough for evolution to occur. In the study that they conducted, researchers
found information on milk consumption across Europe using previous data collected from animal
fat residues found on over 13,000 pieces of pottery from 550 archeological sites. They found the
earliest known evidence of a mutation causing lactase persistence to be around 6,500 years
ago. However, this mutation did not become widespread until just 3,000 years ago. They believe
that lactase persistence was driven by periods of famine and infectious disease outbreaks, by
comparing it with changes in population density. For instance, the spread of salmonella caused
excess deaths in the lactose intolerant population due to malnutrition. It’s suspected that lactase
persistence provided those with the ability to digest lactose with more nutrients than those who could
not digest lactose, thus resulting in fewer deaths. Though this provides a possible explanation of
how lactase persistence emerged, there is still no definitive proposal on how it was able to
spread, according to the study.
Discovering the truth behind the cause of people developing lactase persistence is not an easy
task. The idea of famine and disease in ancient Europe serves as one out of numerous
possibilities that may have driven it. It’s possible that there may not be just one explanation as
lactase persistence may have even evolved in different places at different times. What’s
important is that discovering and analyzing historical evidence can provide us with more insight
on how the lactase gene works and why people developed a persistence for it.
Sarah Belcher (3)
https://www.sciencenews.org/article/lactose-tolerance-milk-famine-disease-ancient-europe
Hi Sarah! This is a particularly interesting topic to me as I have more recently been looking into how the sources of our nutrients have changed overtime as we evolve as a species. I have especially heard discourse between groups of people firmly rooted in either vegan or carnivore diets. Have you heard of any other modern discoveries of how our evolved bodies best absorb nutrients that gives substance to either of these arguments.
ReplyDelete- Anthony Nassar
DeleteHi Anthony! I’m not entirely sure how to answer your question, but I know that there are other ways our bodies have evolved to digest certain foods we weren’t able to before due to the development of agriculture and domestication. Similar to how we are able to digest lactose because of us domesticating cows, it’s likely we evolved to digest certain grains due to us creating farms and growing crops.
DeleteSarah Belcher
Hi Sarah! I thought that this post was really interesting, especially because I had always thought that being lactose intolerant was something that resulted from a genetic defect, rather it being what "should" occur. This post also enlightened me with the history of Europeans building their tolerance for lactose, which I found particularly interesting because from my personal experience, lactose intolerance is a common trait found on my Asian side of the family. Do you think that this explanation is sufficient enough to explain the distribution of lactose intolerance in different races/ethnic groups?
ReplyDelete- Amy Perez
Hi Amy! I do think this could be a reason why lactose intolerance is more prevalent in certain races/ethnic groups because consuming dairy might have not been as common in their food. If you think about it, a lot of Asian food today doesn’t contain much dairy at all, most likely because back then cows were not really found in Asia. Therefore, Asians didn’t evolve to be lactose tolerant like many Europeans have.
DeleteSarah Belcher
Hi Sarah! I always found it interesting that the majority of people I know after eating an ice cream, or mac and cheese would end up with a stomach ache later that day. I remember learning about the lactase enzyme in bio 285 and found it fascinating that some people's pathway stays active while others are deactivated. Do you think it has something to do with the amount of dairy that a person consumes throughout their childhood that determines wether the pathway is activated or deactivated?
ReplyDelete^Brenna MacDonald
DeleteHi Brenna! I also remember learning about lactase in Bio 285 and found it really interesting because I’m lactose intolerant myself, and it made it easier for me to understand what causes me to not digest lactose. To answer your question, I think what determines the lactase gene from being turned on or off has something to do with either the amount of dairy you consume as a child or heredity. I think for some of us, who have history of lactose intolerance in our family, have a much higher chance of being intolerant once we get older, no matter how much we consume as a child. But for people who don’t have a history of lactose intolerance, I think it’s up to how much they continue to consume up to adulthood. As long as they are consistently having dairy in their diet, they should stay lactose tolerant.
DeleteSarah Belcher