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What gave us the ability to become the apes that took over the world comes down to three things: bipedalism, tool-making, and fire use and acquisition. Those three things catapulted our evolution and brain size (number of neurons) and made it possible for us to be human. The cause of our extraordinary cognitive abilities is the number of neurons in our brain in total—16 billion in all. The only thing that could power a brain so energy-demanding is a diet of cooked meat and other foods. This acts as a predigestion outside of the body so more nutrients can get extracted more efficiently, to power a growing brain due to other selective pressures. Clearly, without cooking, our brains we wouldn’t have the cognitive capacity to take over the world.

In 2001 a huge finding was made in Africa, that of an ape with the beginnings of a bipedal pelvis. Soon after, footprints were discovered where the skeleton was found. A huge debate broke out, with researchers wondering how this new finding fit in with our evolution. Since Lucy had the beginnings of a bipedal pelvis, this conserved about 75 percent more energy than walking on all fours did (Sockol, Raichlen, and Pontzer, 2007). Since the human brain is our most costly organ, the advent of bipedalism freed up an immense amount of energy to power our soon to be big brains.

After the advent of bipedalism, we could then manipulate our environment which called for the need for tools. To have the ability to make tools—and make them efficiently—our ancestors needed to have hands and opposable thumbs. Since we are primates just like them, we just happen to have this evolutionary trait. To create a usable stone tool for the right situation, one needed a certain expertise in making that tool. There is evidence that our brain size increased since we needed the expertise to survive in our ancestral past (Skoyles, 2007).

Soon after, our ancestor Homo erectus appeared on the scene. The fossil record shows that our brain size really began to increase around 2 million years ago, (Herculano-Houzel, 2016). What could have driven such a rapid increase in brain size? The advent of cooking. Herculano-Houzel (2016) defines cooking as things cooked with fire, as well as foodstuffs mashed with the stone tools we could now create with our newly freed hands. After these two discoveries, brain size then nearly doubled in size. However, when the neuronal composition of the brain is looked at, it has the number of neurons expected for a brain its size (Herculano-Houzel, 2009). The human brain is not special in its neuronal composition.

Erectus began controlling fire between 1-1.5 mya (Berna et al, 2012). The use of fire softened food, making it easier to chew, decreasing our jaw muscles and size of our teeth which also allowed for our big brains with large amount of cerebral neurons—16 billion in all, the most out of any animal in the animal kingdom, and is the cause of our superior cognitive abilities (Herculano-Houzel, 2016).

Since the human brain is a primate brain, it has some key features that aren’t available in other brains. The most important being that we have the most neurons crowded into our cerebral cortex than other animals. That is the cause for our cognitive superiority over other animals, but not Neanderthals (Villa and Roebroeks, 2014). There is anthropological evidence that our so-called cognitive superiority over the Neanderthals may be a myth, since they discovered no data inferring that we had any ‘superiority’ over Neanderthals in terms of technology, social structure or cognitively.

Without our ability to control and create fire, starting with erectus (Berna et al, 2012), our brains wouldn’t have had the ability to power such a large brain, and thus our brains would have stayed erectus-sized. We can look at the evolution of great apes’ brains (Herculano-Houzel and Kaas, 2011) and say, with confidence, that if our hominin ancestors never would have controlled fire and passed down the useful skill down through the generations then we would not be here today. Looking at it in this way, we can thank the beginnings of cultural transference and acquisition for a large part of the reason why we are here today (mass extinctions and decimations aside). If we would have continued to eat our plant-based diet than our brains would have stayed around 600-800 cc, a size with nowhere near enough neurons for our outstanding cognitive abilities. So, Stephen Jay Gould may be on his way to vindication, as he wrote in his book Full House (1996): “We have no evidence that the modal form of human bodies or brains has changed at all in the past 100,000 years—a standard phenomenon of stasis for successful and widespread species, and not (as popularly misconceived) an odd exception to an expectation of continuous and progressive change.” There is now some evidence to corroborate his theorizing.

When talking about how we evolved to become the ape that took over the world, three things cannot be overlooked: 1) Bipedalism. We know that Lucy was the first hominin to have a pelvis close to our modern one (Harcourt-Smith and Aiello, 2004); 2) we could now stand upright, acquiring kcal was easier and more efficient (Lieberman, 2013); and 3) walking bipedally conserves 75 percent more energy compared to knuckle-walking (Sockol, Raichlen, and Pontzer, 2007). Bipedalism then freed our hands so we could use tools (Marzke, 2011). Furthermore, there are biomechanical reasons for the acquisition of bipedalism: one main factor being that every development of typical human morphology can be explained as adaptations to conserve energy walking long distances (Preuschoft, 2004). Bipedal walking may be one of the most important events in our evolution—for without that, every other great thing you see around you today would not be here since we then would not have the ability to manipulate the environment in which we live.

Just like our capacity for expertise may have increased our brain size, there is evidence that tool making increased our brain size as well (Stout et al, 2015). So this further increased our brain size, and when our brains reached around 800 cc with erectus, the ‘discovery’ of fire was able to occur due to the ability expertise capacity gained from becoming experts with creating tools and learning how to survive. This crude form of cooking (mashing/smashing foodstuffs to extract nutrients) allowed our brains to be fueled by the coming wave of nutrients. Furthermore, since the food was already ‘predigested’, so to speak, it was easier to chew. The softened foods then weakened our jaw muscles (Organ et al, 2011). So, in a way, you can say that human evolution is driven by dietary changes (Luca, Perry and Di Rienzo, 2010).

Conclusion

The advent of bipedalism allowed for the ability to make stone tools, which was one of the first cases of cultural transference. To see how important the use of fire was, one only needs to look at gorillas. Metabolic limitations resulting from the number of hours available to feed along with the low caloric yield of raw foods imposed a limitation on brain size for great apes and gorillas—imposing a tradeoff between the total neuronal amount and body size, making them the outlier in terms of body size (Fonseca-Azevedo and Herculano-Houzel, 2012). Thus, you can see the benefits of cultural transference and acquisition, which gave us the ability to have us become the ape that took over the world with our superior cognitive abilities primarily caused by the advent of cultural transference and acquisition beginning with the advent of bipedalism which allowed us to increase our foraging range, allowing us to consume higher-quality kcal to power our soon-to-be big brains, tool-making, and fire-use.

References

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Dr. John R. Skoyles (1999) HUMAN EVOLUTION EXPANDED BRAINS TO INCREASE EXPERTISE CAPACITY, NOT IQ. Psycoloquy: 10(002) brain expertise

Fonseca-Azevedo, K., & Herculano-Houzel, S. (2012). Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution. Proceedings of the National Academy of Sciences,109(45), 18571-18576. doi:10.1073/pnas.1206390109

Gould, S. J. (1996). Full house: The Spread of Excellence from Plato to Darwin. New York: Harmony Books.

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Herculano-Houzel, S. (2013). The Remarkable, Yet Not Extraordinary, Human Brain as a Scaled-Up Primate Brain and Its Associated Cost.

Herculano-Houzel, S. (2009). The human brain in numbers: a linearly scaled-up primate brain. Frontiers in Human Neuroscience,3. doi:10.3389/neuro.09.031.2009

Herculano-Houzel, S., & Kaas, J. H. (2011). Gorilla and Orangutan Brains Conform to the Primate Cellular Scaling Rules: Implications for Human Evolution.

Herculano-Houzel, S. (2016). The Human Advantage: A New Understanding of How Our Brains Became Remarkable. doi:10.7551/mitpress/9780262034258.001.0001

Lieberman, D. (2013). The Story of the Human Body: Evolution, Health, and Disease. New York: Pantheon Books.

Luca, F., Perry, G., & Rienzo, A. D. (2010). Evolutionary Adaptations to Dietary Changes. Annual Review of Nutrition,30(1), 291-314. doi:10.1146/annurev-nutr-080508-141048

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Organ, C., Nunn, C. L., Machanda, Z., & Wrangham, R. W. (2011). Phylogenetic rate shifts in feeding time during the evolution of Homo. Proceedings of the National Academy of Sciences,108(35), 14555-14559. doi:10.1073/pnas.1107806108

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