By: Students (Stonehill College, BIO323 Evolution, Fall 2018)
It’s pretty possible that you or a few of your peers cannot digest lactose. You may cringe at the thought of eating dairy products. You may even notice that you or your friends get a stomach upset after eating treats like ice cream or have to take a pill before consuming dairy products. Have you ever wondered the biological reason for why some of us can digest lactose and why others cannot? As explained in the article, Impact of Selection and Demography on the Diffusion of Lactase Persistence, different genetic mutations give individuals the ability to digest lactose. Each mutation originates from different regions of the world. Due to lack of sunlight in northern European latitudes and high pastoralism levels in northern African latitudes, populations in these areas benefited most from mutations that allow individuals to digest lactose.
In this podcast, featuring Kirsten Ajello, Rachel Henshaw, and Olivia Porter, we looked at reasons some can digest lactose from an evolutionary perspective. Lactose is a type of sugar found in milk and other dairy products. When foods or drinks containing lactose are consumed, the body needs the help of an enzyme called lactase to break down the lactose sugar into smaller pieces for digestion and absorption. Typically, after weaning off their mother’s milk, individuals lose their ability to digest lactose and become “lactose intolerant” for the remainder of their life. Thanks to a mutation, the ability to digest lactose persists into adulthood among some populations. With this mutation, individuals are able to digest lactose after the weaning phase and this genetic trait is known as lactase persistence. Lactase persistence is common in European and African populations and two hypotheses were researched by Pascale Gerbault et al. to explain why the ability to digest lactose evolved in these specific regions. One of the hypotheses was the gene-culture coevolution hypothesis, which suggested that lactase persistence evolved in pastoral populations because there was a nutritional benefit to the consumption of milk. The second hypothesis was the calcium assimilation hypothesis, which proposed that lactase persistence evolved in Northern Europe due to the lack of sunlight. Sunlight is needed for the synthesis of vitamin D which is necessary for keeping bones strong and healthy. A deficiency in vitamin D will lead to rickets, so consuming dairy is known to supplement the body with vitamin D. Both hypotheses were supported and suggest why these populations could digest lactose.
To draw these conclusions, the scientists analyzed the distribution of lactase persistence traits in parts of Africa with high pastoral levels and Northern Europe due to lack of sunlight. Computer stimulation were used to analyze the evolution of frequencies that were found in Europe. At least three mutations: −13,910 C/T (generally linked to −22,018 G/A) in northern Europe (100% association), −14,010 G/C in East Africa and −13,915 T/G in the Middle-East/North Africa ( Gerbault et al.) were associated with this dominantly inherited trait. Due to social interactions over time, this mutation has spread to different regions around the globe, allowing populations of African and European descent to enjoy the benefits that come with consuming lactose.
You may be lactose intolerant and wondering if you are getting the vital vitamins needed. Well, don’t panic because there is a way! Many foods in our diet which contains lactose are essential sources of calcium, so if you are lactose intolerant, it is critical that you find suitable calcium-rich alternatives. There are lots of lactose-free products available in the market, and this means that you can easily have a calcium-rich product without having to worry about the lactose. Always speak to your dietitian before significantly changing your regular diet to assure you don’t miss out on essential vitamins.