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Imagine traveling back through time to an ancient Africa where our genus Homo was born. Molded by a ruthless natural selection, our ancestors were born and died there again and again. Their lives and deaths were evidenced and honored by their bone prints. Their incomplete remains were bequeathed to us through time to reconstruct their stories. Their stories, we must remember, are also our stories, for they tell us where we came from and how we came to be. To find out more about who we are, we must travel through time to an ancient Africa.

Now that your imagination has delivered you to a prehistoric home, you are about to thrive in this hostile fiery savannah Africa, just like our ancestors. Encountering some of them, you are mouth-openly shocked. Concomitant self-awareness reminds you that they have smaller teeth, just like you do. One of them you see is terribly climbing up and down the tree. “What a bad climber,” you murmur. Although limbs and shoulder are weak, the body is big. So is the head. And, many of them are comfortably roaming on the ground. The amalgamation of these tiny pieces of evidence and your time travelling bout- precisely 1.8 million years makes you conclude that you are meeting Homo erectus. And the larger head confirms your deduction. The bigger cranial size might mean that they might be smart. Yet, you are not entirely sure; you just notice a familiar torn-up human carcass, brought back by a Homo erectus. The carcass possibly is the victim of spotted hungry hyenas. The sky is getting dark too. You wonder how you would avoid being the supper for hungry hyenas when the sun goes down.

All you can long for is three bare essentials: food, water and shelter. Once again, you would be dead wrong because what you need is not food, water and shelter. Instead, you need cooked food, clean water and safe shelter. These can only be acquired with the aid of fire. Our ancestors who mastered the use of fire become lucky ones in passing on their genes. If you abhor the idea of you being a delightful dinner for spotted hyenas, here is a piece of advice to you, “When in Pleistocene, acts like Homo erectus.” To survive like our ancestors, you must tame the fire first. The following guide is to better illuminate the significance of fire use over human history change our preferences for cooked diets so that you would be better prepared, informed and beholden during your next time-travelling trip.

The one book you absolutely should read before your next trip is “Catching Fire. How Cooking Made Us Human.” Through his vivid imagination and solid evidence, Wrangham (2009) proposed the cooking hypothesis. Wrangham argued that Man-the-Hunter theory was not complete in explaining two kinds of Homo transformations: from australopithecines to habilines, and from habilines to Homo erectus. The same Man-the-Hunter cannot account for two changes observed in our lineage. Perhaps, Man-the-Cook could explain the second leap. Wrangham made his case by pointing out biological evidences observed in us. Blunt teeth and smaller guts in humans indicate that humans are not well adapted to eating meat unless cooking is involved. Compared to other apes, humans are also found to be more resistant to Maillard compounds, harmful toxic compounds found in cooked items. This makes sense. Third evidence is found in intestinal digestion that produces useful calories to us. Cooking results gelatinization and denaturation effects in food, yielding humans efficient digestion. Wrangham also presented experimental results that show us how we derive more energy from cooked food than from raw food. Cooked food therefore is central to humans. But can Wrangham explain when cooked food, clean water and safe shelter become extremely important to our human ancestors?

A number of 1,000,000 and 1,500,000 year old relics: burnt bones at Swartkrans in South Africa, heated lumps of clay associated with campfires at Chesowanja in Kenya, heated rocks in a hearth pattern at Gadeb in Ethiopia, etc. hinted the earliest possibility of fire use. However, Wrangham is convinced that the use of fire begins at the earlier time, beginning with Homo erectus, not Homo heidelbergensis. Certain fossil evidence indicated that Homo heidelbergensis was already using fire. The small, but increased cranial capacity changes from Homo erectus to Homo heidelbergensis corresponded very little to changes in the diet due to cooking. Homo erectus could be the answer. Homo erectus’s reduced teeth size, small gut and bigger brain, which you also observed during your trip, reveal that the use of fire begins with Homo erectus. Fire could also explain why Homo erectus you encountered were bad climbers. Homo erectus, Wrangham proposed, slept on the group and depended on the fire to see and scare predators at night. This you might be able to confirm during your next time-travelling visit.

But before your next visit, I suggest you to go to the nearest zoo first. We first need to visit our close existing cousins, great apes, to better understand the significance of cooked food. It is obvious that great apes do not control fire or cook food. But, do they also prefer cooked food like we do? Again, our ancestors could have first controlled fire for warming and lighting, other than cooking. Wobber, Hare and Wrangham (2008) tested this question, using great apes. Since great apes do not control fire, the answer, the authors argued, could hint us whether hominids began to prefer cooked food before or long after the control of fire. If great apes preferred cooked foo, hominins could have adopted cooked diet before or quickly after the control of fire.

In experiment 1, the experimenters offered fourteen chimpanzees various types of tubers such as carrot, white potato and sweet potatoes either coked or raw forms. Each test session, the subject can only make one choice. Chimpanzees in the experiment significantly preferred cooked food, except white potatoes. In experiment 2, the experimenters asked why great apes (14 chimpanzees, three bonobos, two gorillas and four orangutans) preferred cooked food. Is it either because of reduction in toughness or because of reduction in chewing time before swallowing? To test this, carrots were manipulated either in cubes, mashed or grated forms. As hypothesized, the experimenters found that great apes preferred cooked carrots to raw ones, except when it was paired with the mashed carrot, implying that softer item is preferred. The experiment 3 tested whether great apes preferred cooked items to raw ones, using familiar foods such as apples and beef. The great apes significantly preferred cooked forms to raw ones. The experiment 4 also tested this hypothesis using chimpanzees that were not given meat as part of their regular diet. The same results were yielded; chimpanzees significantly preferred cooked meat. These experiments show that great apes preferred cooked food to raw one. Therefore, our human ancestors could have preferred cooked food and quickly adopted cooking after the control of fire. Did our ancestors also possess the cognitive capacities needed to draw the causal relationship between fire and cooked items? If so, the preferences for cooked food might even predate the control of fire.

To answer this question, Warneken and Rosati (2015) studied the mind of chimpanzees who are our closest relatives. Although chimpanzees neither cook nor control fire, Warneken and Rosati (2015) argued that chimpanzees could understand “cooking”, and these general cognitive abilities possessed by chimpanzees would have been shared by our Paleolithic ancestors. Across nine studies using different designs, chimpanzees participated in food preference tests.

In experiment 1, chimpanzee significantly preferred cooked potatoes to raw ones. In experiment 2, chimpanzee went through patience test, either eating a food item immediately or waiting for 1 minute to receive three pieces. Chimpanzees significantly preferred to wait for 1 more minute for three food pieces, when the food is cooked rather than raw. In experiment 3, a special “cooking” device was used. A raw food was shaken in front of the chimpanzee and put into the cooking device that had false bottom. The experimenter then shook it for 5 second. In actual test trials, the cooked piece came out from the device and the raw unchanged piece came out from the other device. Chimpanzees had to select either one or the other. Again, chimpanzees selected the food from the cooking device significantly more than the raw food.

In experiment 4, chimpanzees were tested to see if they can cook on their own; they were given choices either to eat the meat, put into the cooking device or put into the control device on their own. On average, chimpanzees placed the raw food into a cooking device more than 50% of the time. Experiment 5 replicated the experiment 4. Chimpanzees selectively placed food in the cooking device, rather than the control device. Experiment 6 also showed that chimpanzees significantly preferred putting raw potatoes into the cooking device than eating them right away. However, when cooked potatoes were given, chimpanzees preferred to eat them right away, rather than putting them into the cooking device again. In experiment 7, chimpanzees were tested to see if they selectively put edible items into cooking device. When given wood or raw potatoes, chimpanzees significantly preferred putting raw potatoes into the device than putting wood pieces, implying that they did not see the act as purely trading. In experiment 8, chimpanzees were tested whether they would travel longer distance to cook food. They were more likely to put food into the cooking device in the near condition, compared to the far condition. In the last experiment, chimpanzees were shown to put raw food into the cooking device if they anticipated that someone was going to help them cook, compared to the control condition. These series of experiments showed that our ancestors certainly were not dumb or at least smart as modern day chimpanzees who understand cooked food. But, chimpanzees cannot control fire.

Now we can stop looking at great apes and start looking within ourselves. We can ask ourselves why do we enjoy campfires? Lynn(2014) argued that calmer hominids in the past particularly benefitted from the use of campfire, where people would have cooked food, got warmth, defended predators and perhaps performed religious rituals. Lynn(2014) pointed out how !Kung San foragers of the Kalahari Desert stared into the flames and performed rituals.. In Lynn’s (2014) experiments, participants stared into the virtual campfire video on the computer. The participants’ blood pressures were then measured. Pre-and-post analysis showed that participants’ blood pressures decreased among people who looked at virtual fire with the sound on, compared to those who looked at virtual fire only without sound and the virtual fire in the upside-down position (control). The experiment also found increased prosociality scores, as measured by the questionnaire, among participants in the virtual fire with the sound on condition. The study suggested that we became more prosocial, absorbed, and relaxed in front of the campfire, and the effect observed was evolutionarily rooted in us.

You have heard about the book and several experiments, you have become more appreciative about the use of fire and cooked food. Yet, you are saying to yourself, “Wait a minute. What do all these mean?.” Question only begets more questions. Perhaps you might even be more disappointed. You might be asking if fire began with Homo erectus, as postulated by Wrangham in his book. This is hard to confirm. But the earliest possibility of fire use dated back to 1 million year in South Africa may be not controlled by Homo erectus at all. It could be just a fire set by lightning. Since stronger fossil evidence of fire use is found at their sites of Homo heidelbergensis, the fire could only begin with them. Or the use of fire could begin with earlier species like Homo habilis or co-existing Paranthropus. Wrangham thought that Man-the-hunter could not account twice for the increasing brain size. However, it may just be the case that habilis were terrible at hunting, as ample fossil evidence suggests these ancestors ended up many times in the diet of large predators such as jaguar (Smillie, 2002). So, Homo erectus simply became more efficient at hunting, and the increased meat diet, not fire, accounted for increased brain size. And why would Homo erectus need fire at night to ward off against predators. They could have lived in the caves and slept quietly. Wouldn’t fire instead draw the attention of the predators?

Blunt teeth might not be associated with cooked food since Homo erectus already started using stone tools to cut meat. Recently, Zink and Liberman (2016) showed that cutting meats also reduced chewing efforts and increased extra calories available from food. Therefore butchering and tool use, instead of fire, could have made H.erectus’s teeth blunt. So Wrangham’s explanation is a possibility, but not a certainty.

Again, there are issues in Wobber et al. (2008). The authors argued that testing the chimpanzees about their preferences of raw to cooked food would provide them insights into whether ancient ancestors evolve preference for cooked fire sooner after the control of fire. The answer is, “Not necessarily.” The model, based on modern chimpanzees, in the experiment has 2 flaws. First, modern chimpanzees have been coexisting with humans for more than six million years. So the brains of modern chimpanzees are advanced enough, as much as ours, for their species to survive and reproduce. One thing that is sure is that the modern chimpanzees’ brains cannot certainly represent our ancient Homo ancestors’ brains. In fact, modern chimpanzee brain is too advanced for humans to ignore; chimpanzees have recently been freed from biomedical research across the U.S. (Fears, 2015). They have been given chimpanzee rights. Secondly, chimpanzees in the experiment were captive; captive animals display behaviors that are rare or abnormal in natural habitats. So using modern captive chimpanzees to stimulate the brain of our ancient ancestors is highly questionable. The explanatory power is limited in terms of what the results could reveal. It’s like asking modern humans whether they like to live in the wild or the house, to stimulate what chimpanzees, our closest relatives, actually prefer.

The aforementioned flaws apply to (Warneken & Rosati, 2015). Cooked potatoes were preferred by chimpanzees in (Warneken &Rosati 2015), but not by other chimpanzees in (Wobber et al., 2008). This is the reason why captivity is an issue in generalizing the results. However, Warneken and Rosati, (2015) conducted a series of experiments and revealed necessary cognitive capacity for chimpanzees to understand cooking. Yet, chimpanzees in their study were pretty bad at self-regulating. This begs the question of how our earliest ancestors could have begun fire use and cooked food. Did our ancestors have some cognitive capacity to causally link different events or at least some patience to wait for the end product of cooking? So you can certainly argue that big brain leads to cooking, rather than vice versa. This also makes sense since not all of our ancestors would have known how to make fire. They must have learned communicating and observing how others were making fire. And, big brain would facilitate all these processes.

There are also problems that could arise as humans started controlling fire. If cooked foods were so good, our ancestors would have focused on fighting over delicious cooked food. Good news, however, is that controlling fire requires tamer and curious individuals. The extra calories could have also helped our ancestors to be more kind and provide extra food to other members in the group. Instead of fighting over cooked food, our earliest ancestors were mostly likely tamed by fire. Fire tamed humans as much as humans had tamed it. Fire has made men more prosocial. Therefore the result from Lynn (2014)’s experiment is convincing to me. However, the limitation with Lynn (2014)’s study is that the fire was a virtual video. But you could argue that the actual fire would have a stronger effect on our physiology. And modern humans do enjoy actual campfire, despite having all the reasons not to. We have cooked food at stove, heater from warmth and shelters for safety.

Undoubtedly, fire, as well as cooked food, is critical over human evolutionary history. Not only did our ancestors get more calories from cooked food, but also became more prosocial from using fire as they shared, cooked and interacted with others. Evidence also shows that our closest relatives, chimpanzees, have the cognitive capacities to understand cooking to a greater extent. In case you have any doubts on their abilities, watch Kanzi the bonobo making a campfire and toasting marshmallow (Barcroft TV, 2012).

However, the evidence is not unquestionable, as I have discussed several issues with conclusion from the studies with chimpanzees. The evidence for why and when humans started controlling fire is not conclusive. Our ancestors might be playing with stones. Perhaps, your next-time traveling trips would answer all these questions. But, remember you need cooked food, clean water and safe shelter.

 

 

 

References

Barcroft TV. (2012, May28). Ape Makes A Fire: Kanzi The Bonobo Makes A Campfire    [Video file]. Retrieved from https://www.youtube.com/watch?v=EMbWDRzqNhc

Darryl, F. (2015, November 18). NIH ends era of U.S. medical research on      chimpanzees. Retrieved May 09, 2016, from https://www.washingtonpost.com/news/speaking-of-   science/wp/2015/11/18/nih-ends-the-era-of-us-medical-research-on-            chimpanzees/

Lynn, C. D. (2014). Hearth and campfire influences on arterial blood pressure:         Defraying the sosts of the social brain through fireside relaxation. Evolutionary Psychology, 12(5), 983-1003.

Warneken, F., & Rosati, A. Cognitive capacities for cooking in chimpanzees. Proceedings of the Royal Society B: Biological Sciences, 282 (1809).

Wobber, V., Hare, B., & Wrangham, R. (2008). Great apes prefer cooked food. Journal of Human Evolution, 55, 340-348.

Wrangham, R. W. (2009). Catching fire: How cooking made us human. New York: Basic Books.

Zink, K. D., & Lieberman, D. E. (2016). Impact of meat and lower Paleolithic food      processing techqniues on chewing in humans. Nature, 531, 500-503.

 

 

 

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