Brain Size and the Emergence of Modern Human Cognition

This essay, by Ian Tattersall, from Rethinking Human Evolution, is probably the last I'll discuss from the book. Like the other essays, it challenges conventional wisdom regarding human evolution and makes some good points.

For reasons previously explored both by this author (Tattersall 1997, 2015) and by the editor of this volume (Schwartz 2006, 2016), paleoanthropology has been mired since the mid-twentieth century in the beguiling notion that evolution in the hominid family (hominin subfamily/tribe, if you prefer; the difference is notional) has consisted essentially of the burnishing by natural selection of a central lineage that culminated in Homo sapiens. Yet accretions to the hominid fossil record over the same period have, in contrast, consistently shown that hominid phylogeny instead involved vigorous evolutionary experimentation. Over the seven-million-odd years of our family's existence, new species and lineages were regularly thrown out onto the ecological stage, to be triaged in competition with organisms both closely and distantly related. Extinction rates were high to match. Further, it is by now well established that all this took place in the context of constantly oscillating climates and habitats (deMenocal, 2011), to which steady, perfecting adaptation would not have been possible, even in principle.....the gradualist interpretive framework has tenaciously lingered, leading to the widespread application in practice of a strictly minimalist systemic approach that has often been justified by spectacularly contorted reasoning (see Spoor et al. [2007], and Lordkipanidze et al. [2014] for classic examples).

Tattersall looks closely at brain size in various hominids. The generally accepted narrative, which I've mentioned before, is that our ancestors first became bipedal due to climate change and the replacement of forest with savannah; this led to dietary changes in which meat provided a more efficient energy source, and cooperation increased, leading to language development and increased brain size. Tattersall says that, although brain size did increase generally in hominids, there is no evidence that this increase alone correlates with increased intelligence. One hypothesis is that the demands of human childrearing required higher intelligence. Tattersall adopts a different position. He thinks that the development of language in early Homo sapiens provided the main impetus. By about 100,000 years ago, humans were sufficiently adept in the use of symbolic language that they were able to manipulate symbols in their thinking processes, which roughly corresponds with what we think of as intelligence. So, Tattersall's view is that what we think of as intelligence is an unexpected byproduct of the acquisition of language. And, although brain size did initially play a role, it doesn't necessarily now. For example, the now- extinct Neanderthals had larger brains than us but apparently lacked our capacity for symbolic manipulation. Additionally, human brain size has been decreasing for tens of thousands of years. Tattersall compares this to early brute force computers (such as Deep Blue), which had to be large to solve problems, whereas recent, smaller algorithmic computers solve even harder problems more efficiently. On the whole, Tattersall's point is that the development of human cognition did not occur within a context of steady movement toward a likely end; a more accurate description is that, at any given time, nature seems to be conducting various survival experiments for which no outcome is clear. Additionally, energy usage often plays a role in evolution. Neanderthals had large bodies and brains, so they were energy-inefficient compared to humans. Strangely, we are now running into similar constraints with cryptocurrencies and AI, which are already straining our energy resources. It looks as if the evolutionary model for both animals and machines may be the movement to lower energy consumption combined with higher performance. Without the sun, we wouldn't be here.

These thoughts relate to those of other writers I've discussed. For example, Giorgio Vallortigara has shown that even chicks use basic arithmetic and geometry, but without symbols or language. This is a good example of how a cognitive function can become more useful through the use of symbolic reasoning. There is also somewhat of a connection with the work of Vinod Goel, who discusses the evolution of the human brain, which is actually a wider look than Tattersall's discussion. Tattersall is probably only talking about the prefrontal cortex, which is relatively small, and the rest of the human brain is mostly quite ancient. Looking at this only from the present, the determinists I've discussed may have some relevance, because they specifically emphasize human limitations and the variability of skills within the current population. This group includes Robert Sapolsky, Robert Plomin, David Reich and Kathryn Paige Harden. While Tattersall is apparently happy that evolution managed to allow us to be here today, he doesn't discuss the liabilities that we've inherited from our evolutionary past. Having myself observed human behavior for seventy-four years now, there is a lot not to like about it.