By imaging the brains of participants learning to make Stone Age tools, researchers are beginning to unravel the neural connections that may have been responsible for, and formed by, the toolmaking industry of our hominin ancestors (Renfrew et al., 2008; Stout and Khreisheh, 2015; Putt et al., 2017). This research sheds light on our evolutionary past, and helps us to answer the driving question: what, ultimately, makes humans unique?
Figure 1: Oldowan tools (left) were created 2.5-1.5 million years ago by early members of the Homo genus. Acheulian tools (right) were created 1.65 million years ago to 100 000 years ago by later members of the Homo genus, as well as early anatomically modern humans (Erlandson and Braje, 2013)
Until the 1970s, toolmaking was seen as a major factor defining human intelligence (Stout, 2016). Then, new studies showing the ability of other animals such as chimpanzees and dolphins to use tools placed the pointy rocks of our ancestors onto the evolutionary back burner (Stout, 2016). Now, scientists in the emerging field of neuroarchaeology have reopened the case. Researchers at Emory University imaged participants’ brains as they created Palaeolithic stone tools (Figure 1) using a technique called fluorodeoxyglucose positron-emission tomography (FDG-PET), which allows participants to remain active as their brains are imaged (Stout and Khreisheh, 2015). Participants were imaged learning by experimentation, imitation, and verbal instruction. As more complex tools were formed, new areas of the brain became active. Figure 2 shows the areas of the brain that were active when making Oldowan and Acheulian tools (Stout, 2016). Evidence demonstrating a similarity in brain organization between modern humans and early hominins (Balzeau, Holloway and Grimaud-Herve, 2012) allowed researchers to conclude that these same areas were likely active in the brains of human ancestors, meaning hominins who produced Oldowan tools possessed at least the minimal neural connections needed for modern humans to make the same tools (Putt et al., 2017). This means that it is likely that the red areas of the brain experienced some enhancement between the Oldowan and Acheulian periods.
This research does not indicate whether the brain evolved through other factors and resulted in improved ability to make tools, or if the tool production itself caused neural rewiring, and ultimately brain evolution (Stout, 2016). To test this question, the researchers used a form of MRI called diffusion tensor imaging (DTI), which maps white matter fabric tracts to visualise neural connections as participants learned to make stone tools. They found that connections between the areas previously understood to be active during toolmaking (Figure 2) were actually strengthened (Hecht et al., 2014). Therefore, it is plausible that Palaeolithic toolmaking was directly responsible for certain aspects of hominin brain evolution. Although other animals may be able to use tools, a unique combination of environmental circumstances, neural plasticity capabilities, and advantageous timing allowed human ancestors to capitalize on the new ‘engineering niche’ and proliferate into the intelligent species we are today (Stout, 2016).
The ability to understand, manipulate, and draw conclusions about the natural world is a characteristic fundamental to the human condition. Our larger and more complexly-connected brains are often cited as the primary factor defining what makes humans unique and successful, and therefore the evolution of the brain is at the forefront of anthropological research (Stout, 2016). This research gives us insight into the causes, benefits, and potential downfalls of behaviour now known colloquially as ‘human nature’.
References
Balzeau, A., Holloway, R.L. and Grimaud-Herve, D., 2012. Variations and asymmetries in regional brain surface in the genus Homo. Journal of Human Evolution, [e-journal] 62(6), pp.696-706. https://doi.org/10.1016/j.jhevol.2012.03.007
Erlandson, J. and Braje, T.J., 2013. Archaeology and the Anthropocene. Anthropocene, [e-journal] 4, pp.1-7. https://doi.org/10.1016/j.ancene.2014.05.003
Hecht, E.E., Gutman, D.A., Kreisheh, N., Taylor, S.V., Kilner, J., Faisal, A.A., Bradley, B.A., Chaminade, T. and Stout, D., 2014. Acquisition of Paleolithic toolmaking abilities involves structural remodeling to inferior frontoparietal regions. Brain Structure and Function, [e-journal] 220(4), pp.2315-2331. https://doi.org/10.1007/s00429-014-0789-6
Putt, S.S., Wijeakumar, S., Franciscus, R.G. and Spencer, J.P., 2017. The functional brain networks that underlie Early Stone Age tool manufacture. Nature, [e-journal] 0102(2017). https://doi.org/10.1038/s41562-017-0102
Renfrew, C., Frith, C., Malafouris, L., Stout, D., Toth, N., Schick, K. and Chaminade, T., 2008. Neural correlates of Early Stone Age toolmaking: technology, language, and cognition in human evolution. Philosophical Transactions of the Royal Society B: Biological Sciences, [e-journal] 363(1499). https://doi.org/10.1098/rstb.2008.0001
Stout, D., 2016. Tales of a Stone Age Neuroscientist. Scientific American, [e-journal] 25(4s), pp.28-35. doi:10.1038/scientificamericanhumanity0916-28
Stout, D. and Khreisheh, N., 2015. Skill Learning and Human Brain Evolution: An Experimental Approach. Cambridge Archaeological Journal, [e-journal] 25(4), pp.867-875. https://doi.org/10.1017/S0959774315000359