Throughout the study of human evolution, a question that has vexed researchers is why humans have relatively large brains in comparison to our body size. While prospective answers may lie in metabolism, a Florida Tech faculty member is considering something new: the role of body temperature.
Florida Tech assistant professor of astrobiology Manasvi Lingam analyzes the role of temperature in the body-to-brain ratio in his recent paper, The Role of Body Temperature in Regulating Brain and Body Sizes in Hominin Evolution. Through the use of mathematical and computational models, Lingam has found a body temperature change of 1-2 degrees Celsius (1.8-3.6 degrees Fahrenheit) may explain why humans are able to have the body-to-brain ratio they do. This discovery may have a profound impact on better understanding the links between the evolution of our species.
“A lot of body processes, such as respiration and the way we acquire and take in food, are dependent on the body’s temperature, so I thought about what would happen if I raised the temperature a little bit either way,” Lingam said. “It really comes down to the fact that at higher temperatures, your body moves faster so you’re able to acquire food resources faster and rapidly consume them faster.”
Lingam was inspired to analyze human brain-to-body ratios by the mathematical modeling work he does in other fields, such as astrobiology and biophysics. After looking at primates’ relatively smaller brain to large body sizes, he wondered if it would be feasible to have both a larger brain and body. Further research from prior models showed that wouldn’t be possible, as both parts would need large amounts of energy from food intake to maintain function. Lingam also looked at whether nutrient-rich diets were a factor, which opened up another aspect for his models.
While the degree of temperature change is key in Lingam’s research, he noted there are a multitude of factors in the evolution of humans, such as how food is cooked and the nutrients in a diet. However, after finding how much of an impact the temperature change had on the models, Lingam’s next step is to look at exactly where and how these temperature changes have had an impact on the changes of the species. A recent paper published in the medical journal The Lancet showed that a century years ago, Americans had an average body temperature that was 0.6 degrees Celsius (1.1 degrees Fahrenheit) higher than today.
During Lingam’s research, one aspect that stood out was seeing the functional part evolution had on the human body. In the random world of evolution, such as the emergence of the giraffe neck or the extinction of the dinosaurs caused by meteors, Lingam discovered though models that the optimal number of hours a human would need to feed and what their optimal mass would be falls within a factor of three, backing up hypotheses that human evolution was shaped by energetic constraints.
“This work suggests that evolution actually has some type of heuristic optimization process, that it is trying to reach some type of equilibrium, that’s it’s very close to the optimum,” Lingam said. “If I tell you that something is within a factor of three, that’s actually very good, when you take into account evolution is random. Normally with random processes, you don’t expect the math to agree so well with random occurrences.”