Humans Developed Lactose Tolerance During Famines and Epidemics, Study Finds

Our ability to savor dairy delights today may be due to the sacrifice of our ancestors who succumbed to disease and starvation thousands of years ago, according to a new study.

It was previously thought that the genetic variation that allows humans to digest lactose evolved at the same time we started drinking animal milk.

Indeed, the gene prevented the unpleasant symptoms of lactose intolerance, such as diarrhea.

However, a new study by researchers from the University of Bristol and University College London (UCL) suggests that the variation occurred later, in times of famine and infectious diseases.

During these times, when people were already weakened by starvation or disease, drinking milk could have proved fatal for people with lactose intolerance.

As a result, people with the lactose tolerance gene were more likely to survive and pass the gene on to their offspring, increasing its prevalence in society.

“When people are severely malnourished, diarrhea can go from being an inconvenience to a life-threatening condition,” explained Mark Thomas, professor of evolutionary genetics at UCL.

It is known that humans began domesticating animals and consuming their milk around 10,000 years ago.  At that time, all humans were unable to digest lactose, the main sugar in milk, after being weaned from breastfeeding.  However, since then, a genetic variation that allows the body to digest lactose has grown in prevalence.

It is known that humans began domesticating animals and consuming their milk around 10,000 years ago. At that time, all humans were unable to digest lactose, the main sugar in milk, after being weaned from breastfeeding. However, since then, a genetic variation that allows the body to digest lactose has grown in prevalence.

Symptoms of lactose intolerance can be life-threatening if they occur alongside starvation or infectious diarrheal disease.  People without the LP genetic variation were more likely to suffer from this combination than those who did, and therefore less likely to pass on their genes

Symptoms of lactose intolerance can be life-threatening if they occur alongside starvation or infectious diarrheal disease. People without the LP genetic variation were more likely to suffer from this combination than those who did, and therefore less likely to pass on their genes

It is known that humans began domesticating animals and consuming their milk around 10,000 years ago.

At that time, all humans were unable to digest lactose – the main sugar in milk – after being weaned from breastfeeding.

The enzyme that digests lactose is called “lactase”, and it is produced in the small intestine during fetal development.

Once babies stopped breastfeeding, their bodies stopped producing lactase, so they could no longer digest lactose from dairy products.

The sugar would therefore be able to travel to the large intestine and cause symptoms of hypolactasia, or lactose intolerance, including cramps, bloating, diarrhea and flatulence.

However, since then, a genetic variation that continues the production of lactase in the body has increased in prevalence.

This variation is known as lactase persistence (LP), which is found in about a third of all adults today.

Ahead of the new research, published today in Naturethe prevalence of LP was thought to increase just as humans began to regularly consume dairy products.

Milk and its products contain useful calories – minerals like calcium and many micronutrients – so consuming them has given them a nutritional edge.

It was therefore assumed that the LP variation was transmitted by natural selection; where more humans with the LP gene passed their genes on to their offspring than those without.

However, researchers have now found that drinking milk was actually common for thousands of years before the LP gene started to increase in prevalence.

To reach this conclusion, milk fat residues absorbed by unglazed pottery shards used by ancient farmers were studied to determine when populations began to consume milk.

They showed that European farmers collected milk almost 9,000 years ago, but that it increased and decreased in different regions at different times.

WHY ARE SOME PEOPLE LACTOSE INTOLERANT?

When humans first started consuming milk, they were all lactose intolerant.

The enzyme that digests lactose is called “lactase”, and it is produced in the small intestine during fetal development.

After babies stopped nursing, their bodies stopped producing lactase, so they could no longer digest lactose after consuming dairy products.

The sugar could therefore travel to the large intestine and cause symptoms of lactose intolerance, such as bloating and diarrhea.

About 5,000 years ago, humans began developing a gene that continued lactase production.

This is thought to be because starvation and disease are life-threatening when combined with the symptoms of lactose intolerance, so the gene allowed people to survive and pass it on to their offspring.

Now this gene is found in about a third of all adults.

Ancient DNA was also analyzed to see when the LP gene appeared and increased in frequency, as well as modern DNA databases that link it to health outcomes.

Although it revealed that the LP variation first appeared about 5,000 years ago, ancient DNA showed no relationship between changes in milk use over time and selection. natural for the persistence of lactase.

Modern DNA data revealed that there were only small differences in the level of milk consumption between those who were lactase tolerant and intolerant.

Nor were there huge differences between them in symptoms and health outcomes, such as bone density and vitamin D levels.

It is therefore unlikely that the genetic variation occurred because it allowed individuals to digest dairy products without the symptoms of lactose intolerance, since they were so minor.

The researchers then performed statistical modeling to establish which environmental factors actually increased LP in ancient populations.

This included using population size as an indicator of the threat of starvation, as there would be more mouths to feed.

Population density was used as an indicator of infectious disease risk because a denser community meant bacteria could spread faster.

Patterns of these factors were found to correlate with the rise of the LP gene.

Indeed, the symptoms of lactose intolerance can be life-threatening if they occur at the same time as starvation or an infectious diarrheal disease.

People without the LP genetic variation are more likely to suffer from this combination than those with it, so those with LP were more likely to survive and pass on the gene.

“When their harvests failed, prehistoric people would have been more likely to consume high-lactose unfermented milk, exactly when they shouldn’t,” said Professor George Davey Smith, director of the unit. of integrative epidemiology of MRC at the University of Bristol.

The authors concluded: “It appears that the same factors that influence human mortality today led to the evolution of this amazing gene throughout prehistory.”

The fact that the actual symptoms of lactose intolerance are so minor raises questions about whether some people who believe they have it can actually enjoy milk well.

The fact that the actual symptoms of lactose intolerance are so minor raises questions about whether some people who believe they have it can actually enjoy milk well.

The study results suggest that it is difficult to tell whether or not a person has the LP variant, as the symptoms of lactose intolerance can be very mild.

The bodily reactions often attributed to lactose intolerance can also easily be confused with those of other functional bowel disorders.

This therefore raises questions as to whether some people in the UK who think they are lactose intolerant may actually be able to enjoy milk and cheese.

Professor Thomas said: “Often lactose intolerance is blamed when in fact what people have are cow’s milk allergies.

“Milk is extremely nutritious, so it could be a loss for the diet to avoid milk.”

THE GREAT BRONZE AGE MIGRATION WAS FUELED BY MILK

Migration in the Bronze Age was fueled by milk, a recent study has shown.

Migrants from Russia brought lactose tolerance genes to Europe, researchers say.

During the last ice age, milk was essentially a toxin for adults because, unlike children, they could not produce the enzyme needed to break down lactose.

But as farming began to replace hunting and gathering in the Middle East around 11,000 years ago, cattle farmers learned to reduce lactose to tolerable levels by fermenting milk to make cheese. or yogurt.

Read more: The Great Bronze Age Migration Was Fueled By Milk

During the early Bronze Age, a mass migration of people from the steppes of Russia embarked on a series of journeys that would change history.  Now a new analysis of dental calculus (pictured) has revealed the secret to their success was quite simple: they drank milk

During the early Bronze Age, a mass migration of people from the steppes of Russia embarked on a series of journeys that would change history. Now a new analysis of dental calculus (pictured) has revealed the secret to their success was quite simple: they drank milk

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