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SHIFTS IN CLIMATE are well-documented engines of biological change. As the world warms, we’re effects that range from birds getting smaller to lizards prematurely aging—all in an attempt to adapt to climatic stresses. Being a part of the kingdom Animalia, humans are not immune to these evolutionary changes, and a recent paper published in the journal Brain, Behaviour, and Evolution suggests that Homo sapiens’ most vital organ—the brain—could be shrinking as the world warms.
“Understanding how the brain has changed over time in hominins is critical but very little work has been done on this subject,” cognitive scientist and co-author of the study Jeff Morgan Stibel told PsyPost. “We know the brain has grown across species over the past few million years but we know very little about other macroevolutionary trends.”
A previous study from the University of Cambridge showed that a human’s body grows in size proportional to climate—bodies grow bigger when it’s colder so as to lose less heat, and vice versa. But Cambridge scientists found that increases in brain size specifically were more likely due to a decreased presence of vegetation (such as the Eurasian steppe) in the area. A lack of vegetation was linked to increased hunting, which was a complex action that fostered the growth of a larger brain.
However, Stibel’s research of macro-evolutionary trends finds that the human brain has actually decreased in size, due to the warming of the Holocene period. Stibel examined 298 skulls from the past 50,000 years, which allowed for an analysis of two different climatic periods—before and after the last Ice Age. Each skull underwent 373 independent capacity measurements and were measured against four climactic records.
Stibel’s research found that human brain size decreased 10 percent during the general warming of the Holocene. He also discovered that humidity and precipitation influenced brain size as well (more rain = bigger brain), but to a much lesser degree than warming temperatures. Of course, a smaller brain doesn’t mean future humans will de-evolve into less-intelligence primates. Scientists have found very little correlation between absolute brain size and overall smarts.
Regardless, Stibel says this study shows that human biology is driven by natural selection as influenced by environmental pressures. And as Earth begins to warm more rapidly, it’s uncertain how this will affect human physiology hundreds and thousands of years into the future.
Hopefully, humans will still be around to find out.
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.
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