Mustafa Vora, DY Patil University, Navi Mumbai
In a recent study, a team of researchers compiled the measurements of brain and body size of over 300 fossils of Homo around the globe with the world’s regional climate over the last million years. This study showed how the size of the brain and body fluctuated over time by pinpointing the specific climate experienced by the fossils when they were living and comparing it with the modern-day Homo species that is Homo sapiens.
What does Bergmann’s rule say about this?
According to Bergmann’s rule, species of larger size are found in colder environments, while species of smaller size in warmer regions. When the mass of a body is large relative to its surface area then less heat is lost. A larger size is favorable in colder climates as the body requires more energy for generating heat and also for storage of food as energy is been utilized faster in comparison to warmer climates.
The present study of interest:
Although our species, Homo sapiens has emerged around 300,000 years ago in Africa, the genus Homo has existed much longer than that. It includes Neanderthals and other extinct but related species such as Homo habilis and Homo erectus. During the evolution of the genus Homo, the size of the brain and body has fluctuated dramatically. Compared to the earlier species, Homo erectus, our body is 50% heavier; Our brain is three times larger. However, what impacts these changes remains highly debatable. The most well-known and tested hypothesis for the phenotypic relationship to the environmental factors is Bergmann’s rule. Furthermore, other hypotheses focused not only on absolute temperature but also on biomes, precipitation, and seasonal, intra-annual, and millennial variation in these variables.
Researchers formulated four broad hypotheses for the evolution of brain and body size in relevance with the context of hominin evolution. Their interest in these hypotheses was mainly to explain how the larger bodies and brain sizes evolve. “The formulated hypotheses are distinguished from each other by the type of mechanism that underlies them and not just a specific environmental variable” as mentioned by a recent study published in the journal Nature communication. The hypotheses are; Environmental Stress Hypothesis, Environmental Constraints Hypothesis, Environmental Variability Hypothesis, and Environmental Consistency Hypothesis.
What did the study find?
The study found that different factors determine brain size and body size, meaning they are not under the same evolutionary pressures. When compared to brain size, the environment has a much greater influence on the body size of the Homo genus. For maintaining the growth of our large and energy-demanding brain, the amount of nutrients gained from the environment needs to be adequate. This points towards an indirect environmental influence on brain size in more stable and open areas rich in nutrition.
Along with this, the researchers found that non-environmental factors were more important for the evolution of larger brain size and not just the climate. It may be because of the challenges of increasingly complex social life posed upon the brain for cognitive functioning, the variation in intake of diet, and more sophisticated technology.
Significance of the study:
Evolution is inevitable; there is a shred of good evidence that the human body and brain size continue to evolve to survive in different conditions. The researchers say the brain size in our species is shrinking since the beginning of the Holocene (11.650 years ago). Our brain will shrink even more if our species continue to depend on technology, like outsourcing complex tasks to computers. And this may not take more than a few thousand years to happen.
It is fascinating to know what will happen in the future to our body and brain sizes, but extrapolating the results based on the last million years is not the key because so many factors can change.
Also read: The Art of Dreaming, According to Science
Reference:
- Will, M., Krapp, M., Stock, J. T., & Manica, A. (2021). Different environmental variables predict body and brain size evolution in Homo. Nature Communications, 12(1), 4116. https://doi.org/10.1038/s41467-021-24290-7
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