Climate Change Influences Brain Size in Humans

Abstract

Brain size evolution in hominins constitutes a crucial evolutionary trend, yet the underlying mechanisms behind those changes are not well understood. Here, climate change is considered as an environmental factor using four paleoclimate records testing temperature, humidity, and precipitation against changes to brain size in 298 Homo specimens over the past fifty thousand years. Across regional and global paleoclimate records, brain size in Homo averaged significantly lower during periods of climate warming as compared to cooler periods. Geological epochs displayed similar patterns, with Holocene warming periods comprising significantly smaller brained individuals as compared to those living during glacial periods at the end of the Late Pleistocene. Testing spaciotemporal patterns, the adaptive response appears to have started roughly fifteen thousand years ago and may persist into modern times. To a smaller degree, humidity and precipitation levels were also predictive of brain size, with arid periods associated with greater brain size in Homo. The findings suggest an adaptive response to climate change in Homo brain size that is driven by natural selection in response to environmental stress.

Commentary: Human brains have shrunk: the questions are when and why

“…Thus, the reduction in the endocranial volume in the period 5 ka ≥ age > 0.15 ka should be considered as a reliable conclusion. A better sex-balanced 5 ka ≥ age > 0.15 ka dataset would have given a still lower value of p. Thus, the above analysis confirms the result of DeSilva et al (2021DeSilva et al ( , 2023 of an endocranial volume reduction during the last 3-5 ka and discussed by several other authors (von Bonin, 1934;Tobias, 1970;Schwidetzky, 1976;Wiercinski, 1979;Beals et al, 1984;Henneberg, 1988Henneberg, , 1998Henneberg, , 2004Brown, 1992;Steyn, 1993, 1995;Ruff et al, 1997;Brown and Maeda, 2004;Wu et al, 2007;Bailey and Geary, 2009;Hawks, 2011;Balzeau et al, 2013;Bednarik, 2014;Liu et al, 2014;Stibel, 2021Stibel, , 2023Wu et al, 2022).…”

Clockwork Orangutan: microRNAs, thermoregulatory tradeoffs, and the evolution of brain size

“…During exercise with progressive hyperthermia, human brain temperature increases in parallel with that of the body core, leading to hyperthermia and fatigue (Nybo, 2012; Nybo and Gonález-Alonso, 2015; Tsuji et al, 2016). Over a period spanning 700,000 years of human evolution, body mass and shape varied inversely with temperature, indicative of selection in response to thermoregulatory demands (Stibel, 2023).…”

Nanotechnology to Transform the Current Educational System

“…Memory can be organised into a greater word length and/or address space than what is provided by each integrated circuit by merging many chips-often but not always a power of two. (Jeff Stibel, 2017) A memory chip may execute two basic operations: "read," in which the data contents of a memory word are read out (without causing any damage), and "write," in which data is written in a memory word, overwriting any data that has already been there. With each read or write operation, multiple words are accessible in some of the most recent memory chip types, such as DDR SDRAM, to boost data rate.…”