Why Did Humans’ Bones and Skeletons Become Lighter Over the Last 10,000 Years? — Here’s What Scientists Suggest

Looking at our ancestors’ fossils and skeletons, we could observe that ours pales in comparison when it comes to their weight and robustness. This is because our bodies have changed and are continuing to change based on our lifestyle, environment, and needs for survival.

However, what exactly triggered our evolution as humans to have our bones and skeleton become lighter and less robust, especially during the last 10,000 years? Did its development negatively impact our lives, or is it just our body’s response to our new way of life? Let’s explore these ideas and discover the theories that could explain how our bones and skeletons became lighter over the last few thousand years.

Lifestyle Shift — From Hunter-Gatherers to Settled Farmers

A long time ago, over 12,000 years ago, our ancestors were still hunter-gatherers. This meant that they probably did not deliberately grow their own food, but instead relied on the resources readily found in nature. They hunted animals for meat and gathered edible wild plants. They would also migrate to a new environment once their current habitat got depleted because of climate change or natural exhaustion from human foraging.

Their lifestyle is quite hard because it requires them to use their bodies for physically demanding activities to survive. They chased their prey under the scorching heat of the sun, they carried heavy loads for hours and days, they would walk long distances to find food or a new habitat, and they climbed mountains for cave shelters and to seek escape from harsh conditions like floods or wildfires.

In other words, this physically demanding life may have created an evolutionary advantage for individuals with heavier and stronger bones to survive and pass on their genes.

On the other hand, around 12,000 to 10,000 years ago, they transitioned to farming and agriculture. Their daily jobs were still hard, but it is less physically demanding than the hunter-gatherer lifestyle overall. It also contained repetitive tasks that they soon created tools for to make it easier and more efficient.

This massive lifestyle shift over a few thousand years may be one of the most significant reasons why our bones and skeletons became lighter. It is because we utilize them less, easing the selective pressure for these parts of our bodies to become more dense and robust to be able to carry on the survival tasks of a hunter-gatherer.

Read more: Cambridge University

Diet and Nutrition Change — How Food Affects Bones

Human Evolution | Skeletal Structure

Another big factor that could have affected how strong and heavy our bones are is the change in diet. When the hunter-gatherers transitioned to farming, they also had a massive shift in the nutrition they consumed. Before, they would have a variety of food sources, such as wild animals and plants from different habitats. This phenomenon created a healthier mix of nutrients like proteins, minerals, and vitamins necessary for bone development and maintenance.

However, for early farmers, their diet was reduced to the grains and crops they were successful in growing in their lands. They also had select animals that they were able to domesticate. This change to a much narrower diet meant less protein and fewer micronutrients.

Over time, as more children grow with fewer varieties of nutrients and less physically demanding work, the population’s bones and skeletons may develop to be weaker and lighter. In other words, the transition to farming, accompanied by a shift in diet, could have greatly contributed to humans having lighter skeletons over many generations.

Bone Biology & Mechanics — Why Bones Adapt

Human bones and skeletons are living tissues made up of living cells that are constantly being repaired and renewed. Their growth and maintenance respond to how much they are worked, loaded, and pressured. When bones are regularly heavily utilized, such as walking long distances while carrying heavy luggage, hunting wild animals, or climbing mountains, they grow to be stronger and denser.

However, the opposite could also be true, where if our bones are less utilized on a daily basis, they could also become lighter and less robust. So, the human bones’ density may be heavily affected, not just by genetics, but also by their habitual use in various strenuous tasks. This may be why when we shifted from nomadic hunter-gatherers into sedentary, less mobile, and less active farmers, our skeletons developed to be weaker and lighter over thousands of years and many generations.

Read more: PubMed Central

What This Means for Modern Humans

The Story of the Human Body: Evolution, Health, and Disease

The fact that our bones became lighter over thousands of years may have some important implications in today’s world. One is that they may be more vulnerable to fractures and certain bone diseases. Additionally, over time, this implication may worsen if the trend of a sedentary lifestyle is continued and remains prevalent even in the future.

However, this information also meant that we could improve and grow stronger bones and skeletons if our population is exposed to a better environment and conditions that allow for a healthy amount of physical load, and good nutrition from a varied diet. It may require some time and possibly multiple generations to reverse the trend, but what’s important is that we understand that our skeletons and bones are shaped by lifestyle, environment, diet, and our history.

Author's Final Thoughts

Around 10,000 years ago, humans’ bones became lighter and less dense gradually. Researchers think that it could be because of a multitude of factors brought by our change in lifestyle and environment. When our hunter-gatherer ancestors transitioned to farming and agriculture, they also left behind their more physically demanding way of life.

Additionally, the new diet from early farming has less variation of nutrients, possibly causing humans to consume less protein and fewer micronutrients. Both of these factors could have affected our bone density and weight because our skeletons are living tissues that grow and shrink in response to how much load they carry habitually, and the nutrition they receive to be repaired and renewed.

Our bones and skeletons are part of our bodies that tell us a story about our lives in the past, and the changes we have made since then. These bones and skeletons hold the tale about how our ancestors lived and how they changed to become who we are today.

Read next: Why Have Humans’ Jaws Gotten Smaller Over the Last 10,000 Years? — Here’s What Researchers Found

References & Further Reading

Chirchir, H., et al. (2015). Recent origin of low trabecular bone density in modern humans. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1411696112

Ruff, C. B., et al. (2015). Gradual decline in mobility with the adoption of food production in Europe. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1502932112

Ryan, T. M., & Shaw, C. N. (2015). Gracility of the modern Homo sapiens skeleton is the result of decreased biomechanical loading. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1418646112

Larsen, C. S. (1995). Biological changes in human populations with agriculture. Annual Review of Anthropology. https://doi.org/10.1146/annurev.an.24.100195.001153

Macintosh, A. A., Pinhasi, R., & Stock, J. T. (2016). Early life conditions and physiological stress following the transition to farming in Central/Southeast Europe: Skeletal growth impairment and 6000 years of gradual recovery. PLOS ONE. https://doi.org/10.1371/journal.pone.0148468