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I hold the position that the creation and management of man-made fire was a pivotal driver in our brain size increase over the past 2 my. However, evidence for fire use in early hominins is scant; a few promising locations have popped up over the year, the most promising being Wonderwerk Cave in South Africa (Berna et al, 2012). Much more recently, however, it was discovered in Koobi Fora, Kenya, that there was evidence of fire use by Erectus 1.5 mya (Hlublik et al, 2017).
Hlublik et al (2017) identified two sites at Koobi Fora, Kenya that have evidence of fire use 1.5 mya, and Erectus was the hominin in that area at that time. Hlublik et al (2017) conclude the following:
(1) Spatial analysis reveals statistically significant clusters of ecofacts and artifacts, indicating that the archaeological material is in situ and is probably the result of various hominin activities during one or a few occupation phases over a short period of time. (2) We have found evidence of fire associated with Early Stone Age archaeological material in the form of heated basalt (potlids flakes), heated chert, heated bone, and heated rubified sediment. To our knowledge this is, to date, the earliest securely documented evidence of fire in the archaeological context. (3) Spatial analysis shows the presence of two potential fire loci. Both loci contain a few heated items and are characterized by surrounding artifact distributions with strong similarities to the toss and drop zones and ring distribution patterns described for ethnographic and prehistoric hearths (Binford 1983; Henry 2012; Stappert 1998).
This is one of the best sites yet for early hominin fire control. This would also show how the biologic/physiologic/anatomic changes occurred in Erectus. Erectus could then afford a larger brain and could spend more time doing other activities since he wasn’t constrained to foraging and eating for 8+ hours per day. So, clearly, the advent of fire use in our lineage was one of the most important time frames in our evolutionary history since we could extract more energy from what we ate.
Carmody et al (2016) identified ‘cooking genes’ that were under selection between 275-765,000 ya. So we must have been cooking, in my opinion, before 765,000 ya, which would have then brought about the genetic changes due to a large shift in diet—which would have been cooked meat/tubers. Man’s adaptation to cooked food is one of the most important things to occur in our genus, because it allowed us to spend less time eating and more time doing. This change to a higher quality diet began in early Erectus (Aiello, 1997), which then shrank his teeth and gut. If Erectus did not control fire, the reduction in tooth size needs to be explained—but the only way it can be explained is through the use of cooked food.
Around 1.6 my there is evidence of the first human-like footprints/gait (Steudel-Numbers, 2006; Bennett et al, 2009). This seems to be the advent of hunting parties and cooperation in hominins to chase prey. The two new identified sites at Koobi Fora lend further credence to the endurance running hypothesis (Carrier, 1984; Bramble and Lieberman, 2004; Mattson, 2012), since without higher quality nutrition, Erectus would not have had the anatomic changes he did, nor would he have the ability to hunt due to being restricted to foraging, eating, and digesting. Only with higher quality energy could the human body have evolved. The further socialization from hunting and cooking/eating meat was also pivotal to our brain size and evolution. This allowed our brains to grow in size, since we could have high-quality energy to power our growing set of neurons.
The growth pattern of Nariokotome boy (formerly called Turkana boy) is within the range of modern humans and does not imply that he had a growth pattern different from that of modern humans (Clegg and Aiello, 1999). It’s interesting to note that Nariokotome boy, one of the best preserved Erectus fossils we have discovered to date, had a similar growth pattern to modern humans. Nariokotome boy is estimated to be about 1.6 million years old, so this implies that we had similar high-quality diets in order to have similar morphology. It is also interesting to note that Lake Turkana is near Koobi Fora in Kenya. So it seems that basic human morphology emerged around 1.5-1.6 mya and was driven, in part, by the use and acquisition of fire to cook food.
This is in line with the brain size increase that Fonseca-Azevedo and Herculano-Houzel (2012) observed in their study. Metabolic limitations of herbivorous diets impose constraints on how big a brain can get. Herculano-Houzel and Kaas (2011) state that Erectus had about 62 billion neurons, so given the number of neurons he had to power, he’d have had to eat a raw, herbivorous diet for over 8 hours a day. Modern humans, with our 86 billion neurons (Herculano-Houzel, 2009; 2012), would need to feed for over 9 hours on a raw diet to power our neurons. But, obviously, that’s not practical. So Erectus must have had another way to extract more and higher-quality energy out of his food.
Think about this for a minute. If we ate a raw, plant-based diet, then we would have to feed for most of our waking hours. Can you imagine spending what amounts to more than one work day just foraging and eating? The rest of the time awake would be mostly spent digesting the food you’ve eaten. This is why cooking was pivotal to our evolution and why Erectus must have had the ability to cook—his estimated neuron count based on his cranial capacity shows that he would not have been able to subsist on a raw, plant-based diet and so the only explanation is that Erectus had the ability to cook and afford his larger brain.
Wrangham (2017) goes through the pros and cons of the cooking hypothesis, which hinges on Erectus’ control of fire. Dates for Neanderthal hearths have been appearing later, however nowhere near close enough to when Erectus was proposed to have used and controlled fire. As noted above, 1.6 mya is when the human body plan began to emerge (Gowlett, 2016) which can be seen by looking at Nariokotome boy. So if Nariokotome boy had a growth pattern similar to that of modern humans, then he must have been eating a high-quality diet of cooked food.
Wrangham (2017) poses two questions if Erectus did not control fire:
First, how could H. erectus use increased energy, reduce its chewing efficiency, and sleep safely on the ground without fire? Second, how could a cooked diet have been introduced to a raw-foodist, mid-Pleistocene Homo without having major effects on its evolutionary biology? Satisfactory answers to these questions will do much to resolve the tension between archaeological and biological evidence.
I don’t see how these things can be explained without entertaining the fact that Erectus did control fire. And now, Hlublick et al (2017) lends more credence to the cooking hypothesis. The biological and anatomical evidence is there, and now the archaeological evidence is beginning to line up with what we know about the evolution of our genus—most importantly our brain size, pelvic size, and modern-day gait.
Think about what I said above about time spent foraging and eating. Looking at gorillas, for instance, they have large bodies partly due to sexual selection and the large amounts of kcal they consume. Some gorillas have been observed to have consumed food for upwards of 10 hours per day. So, pretty much, you can have brains or you can have brawn, you can’t have both. Cooking allowed for our brains as we could extract higher quality nutrients out of our food. Cooking allowed for the release of a metabolic constraint—as seen with gorillas. It wouldn’t be possible to power such large brains without the addition of higher quality nutrition.
One of the most important things to note is that Erectus had smaller teeth. That could only occur due to a shift in diet—masticating softer foods leads to a subsequent decrease in tooth and jaw size. Zink and Lieberman (2016) show that although fire-use/cooking was important for mastication. Slicing meat and pounding tubers improved the ability to breakdown food by 5 percent and decreased masticatory force requirements by 41 percent. This, too, led to the decrease in jaw/tooth size in Erectus, and the advent of cooking with softer/higher-quality food led to a further decrease ontop of what Zink and Lieberman (2016) state, although Zink and Lieberman (2016: 3) state that “the reductions in jaw muscle and dental size that evolved by H. erectus did not require cooking and would have been made possible by the combined effects of eating meat and mechanically processing both meat and USOs.” I disagree and believe that the two hypotheses are complimentary. A reduction would have occurred with the introduction of mashed food and then again when Erectus controlled fire and began cooking meat and tubers.
In conclusion, the brain size increases that are noted in Erectus’ evolutionary history need to be explained and one of the best is that he controlled fire and cooked his food. There are numerous lines of evidence that he did, mostly biological in nature, but now archaeological sites are beginning to show just how long ago erectus began using fire (Berna et al, 2012; Hlublick et al, 2017). Many pivotal events in our history can be explained by our shift in diet to softer foods due to the advent of cooking, like smaller teeth and jaws to the biologic and physiologic adaptations that occurred after the shift to a new diet. Erectus is a very important hominin to study, because many of our modern-day behaviors began with him and by better understanding what he did and created and how he lived, we can better understand ourselves.