Several major dietary shifts in human evolution, including meat-eating, cooking, and the domestication of plants and animals, have occurred through cultural innovation and changes in available food types with shifting habitats. Identifying adaptations to these dietary changes in the human genome sheds light on the evolutionary history of our species’ metabolism.
The Evolution of Sugar Consumption
Once upon a time, sugar was sold as a spice, used as medicine, and was a luxury food only the rich could afford. However, by the 19th century, sugar became a staple of the working-class diet and was often used as a food preservative, such as in jam.
Types of Sugar
What we casually refer to as table sugar is sucrose, but there are several other types of sugars:
| Type of Sugar | Source of Sugar |
|---|---|
| Sucrose | Sugar cane |
| Glucose | Honey |
| Fructose | Most fruits |
| Lactose | Milk and milk products |
The human body can produce energy only from glucose, so the digestive system must break down other types of sugar, including lactose, into glucose before they can be absorbed into the bloodstream. Types of sugars that cannot be broken down into glucose end up in the large intestine for excretion.
Lactose Sugar
The enzyme lactase helps the human body break lactose into glucose. This enzyme is produced in high quantities at birth to break down the lactose in mothers’ milk. However, as infants grow, their reliance on mother’s milk decreases, and the production of lactase often diminishes. Consequently, many lactose-tolerant infants become lactose intolerant adults.
Lactose intolerant adults lose the ability to digest lactose in their intestines, causing undigested sugar to pass into the large intestine, where bacteria break it down, leading to gas, bloating, stomach cramps, and diarrhea.
Lactose Intolerance Distribution
Most people worldwide are lactose intolerant, but the distribution is not homogenous due to genetic factors. For instance, nearly all adults in Ireland and Great Britain, and most adults in the rest of Europe, can consume milk and dairy products without problems. In contrast, in regions where ethnic Europeans are a minority, most or nearly all individuals are lactose intolerant.
Early Europeans and Lactose Tolerance
Early modern humans who migrated to Europe were mostly lactose intolerant. However, the ability to digest milk and dairy products from domesticated animals was a favorable trait that created a bottleneck in Europe. Lactose intolerance was such a disadvantage that individuals who could digest lactose were more likely to survive and pass on their genes.
Importance of Lactose Tolerance in Europe
Most scientists believe lactose tolerance was critical in Europe for several reasons:
Vitamin D: Less sun exposure in Europe increased the need for vitamin D found in cow’s milk.
Safe Drinking Alternative: Cow’s milk provided a safer and cleaner alternative to potentially contaminated drinking water.
Survival: Those who could not tolerate lactose risked starvation, while those who could tolerate it had a better chance of survival.
The Takeaway
In conclusion, historically, lactose intolerant Europeans were more likely to die from starvation, vitamin D deficiency, or drinking contaminated water before having children, compared to those who could digest milk and dairy products past infancy. As a result, 70% of ethnic Europeans are lactose tolerant today, while lactose tolerance remains an anomaly in other ethnic groups.
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