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

If you look at the fossils of our distant ancestors, you would be able to notice that their jaws are much larger and wider than ours, the modern humans. This change happened relatively recently in the evolutionary history of humans. One of the most drastic changes gradually happened around 10,000 years ago, a time when humans were transitioning from hunter-gatherer societies to farming and agriculture.

It is logical to think that this change in lifestyle is what could have contributed to the decline in size of our jaws, but researchers found that there may have been a multitude of factors affecting this shift. So, in this article, let’s explore some of these theories and reasons that could have caused the humans’ jaws to shrink over the last 10,000 years.

Diet, Chewing Demands, and Working the Jaw

Before the advent of farming, most humans lived as hunter-gatherers. They would hunt animals for meat and collect wild plants that are edible. They focused on gathering the resources that are readily available to them in nature. But when those food supplies got depleted, either because of climate change or overexploitation, they would migrate to another place that has more abundant resources.

During this period, the hunter-gatherers would eat tough foods that were hard to chew, such as raw meat, underground roots, nuts, and other wild plants. This diet would have required them to have a strong and wide jaw capable of chewing through the hard materials. So, it became an evolutionary advantage and most likely created a selective pressure. The individuals who are able to gather and consume the tougher food sources are the ones most likely to survive and pass on their genes to the next generation.

However, about 12,000 to 10,000 years ago, these very same hunter-gatherers started farming and agriculture for a variety of reasons, including but not limited to a more favorable climate, the end of a glacial period or ice age, and abundance of resources in particular regions. In this new lifestyle, their diet became softer.

When agriculture developed, food processing became common, where early farmers ground grains and cooked meat. These phenomena created new food sources that do not require the strong and wide jaws that were previously needed, thus the advantage and selective pressure decreased.

Over time, since our jaws do not need to work as hard, the bone has become less robust. A direct comparison of jaws between early farmers and older hunter-gatherers supported this theory. Additionally, other animals that were fed a softer diet also showed signs of the development of smaller jaws and weaker muscles. In other words, the humans’ transition to farming and a softer diet could be the most significant reasons for the change in our jaw size and strength today.

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Childhood Growth, Function, and Developmental Changes

What Did Humans Evolve To Eat?

The development of our jaws is especially important during the formative years of our lives. When our ancestors transitioned to a softer diet, it also meant that the children still growing up would not be exposed to tougher foods that are hard to chew. These previous diets and lifestyles most likely helped children develop their jaw and face bones more strongly, but the new one with a softer diet and less work for the jaws may have made the development of the jawbone less robust.

Additionally, the modern lifestyle continued and furthered this trend, thus it may have contributed to the decline of jaw size and strength in humans. Nowadays, our infants are fed with a heavily processed diet that was made to be soft and easier to chew. Over time, and many generations, this change in lifestyle may have influenced how the jaw grows, and has created a jaw-shrinking trend in our species.

Breathing, Health, Lifestyle, and Jaw Development

Another reason that could have contributed to the decline in jaw size and strength that is not related to diet is our breathing patterns and certain modern habits. One prominent example is the advent of chronic mouth-breathing patterns, where humans breathe through their mouths instead of their noses. This phenomenon created less muscle pressure and caused the jaw to grow narrower and backward, leading to a shrinking jaw trend in the population.

This is primarily driven by our environment and daily lives, which lead us to another factor, which is an indoor and less active way of life. The modern indoor lifestyle, where we stay on our couch to watch Netflix and work or play on our computers all day, may have also contributed. This is because it made us more sedentary, where our jaws and facial muscles are less active and utilized. Our bones and bodies may have responded by growing smaller and weaker jaws over time.

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What This Means for Modern Humans and Health

Epidemic of Jaw Shrinkage: A Serious But Little Recognized Environmental Problem

A smaller jaw may not necessarily be negative, as it is more of a response to our lifestyle changes over thousands of years. However, some parts of our bodies may not have enough time to adapt yet, such as our teeth. So, the trend of shrinking jaws could have also contributed to more dental problems among humans. It leads to crooked teeth and crowding because of less space in our jaw for all the teeth.

But this phenomenon is still a good example for us to learn about how our biology is affected by our changes in lifestyle. With our technology advancing faster than ever in all fields and industries, it is undeniable that we will face even more lifestyle changes in the future. So, this jaw-shrinking trend should be able to show us how rapid changes could lead to anatomical shifts in our species, preparing us for the future.

Author's Final Thoughts

Humans’ jaws have shrunk gradually over the last 10,000 years. There are several factors that researchers discovered could have influenced this shift. One of the reasons is our species’ transition from hunting and gathering resources to farming and agriculture.

Another factor that could have contributed is our lifestyle changes, such as having a softer diet since childhood, the prevalence of mouth-breathing, and an overall less active way of life. Understanding this whole phenomenon of a shrinking jaw in humans gives us insights into how changes in our lifestyle could affect our health, and how future generations of humans will grow.

As our technology advances faster than ever, we should expect and be prepared for its continual growth and how it could shape our daily habits. We could be facing more future anatomical shifts as our bodies adapt to the world that we are creating.

Read next: Why Did the Ancestors of Humans Evolve an In-Built Fear of Snakes and Spiders Around 40–60 Million Years Ago? — Here’s What Researchers Suggest

References & Further Reading

Katz, D. C., Grote, M. N., & Weaver, T. D. (2017). Changes in human skull morphology across the agricultural transition are consistent with softer diets in preindustrial farming groups. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1702586114

von Cramon-Taubadel, N. (2011). Global human mandibular variation reflects differences in agricultural and hunter-gatherer subsistence strategies. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1113050108

Pinhasi, R., Eshed, V., & von Cramon-Taubadel, N. (2015). Incongruity between affinity patterns based on mandibular and lower dental dimensions following the transition to agriculture in the Near East, Anatolia and Europe. PLOS ONE. https://doi.org/10.1371/journal.pone.0117301

Corruccini, R. S. (1984). An epidemiologic transition in dental occlusion in world populations. American Journal of Orthodontics. https://pubmed.ncbi.nlm.nih.gov/6594064/

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