We are all historians. This fact is fundamental to our existence. It is a key to our humanity.
We tell stories every day. They’re histories — narratives about what went before. We tell them to ourselves, and we tell them to other people. Sometimes we don’t even know that we’re doing it, but even our most mundane actions draw on our sense of the past. Consider the ritual of making dinner. We return home from work and think, “what will I eat this evening?” At that moment, our brains perform a number of complex functions. Some of them are non-conscious. Our brains gauge our need for calories and desire for food. But just as important are a number of other conscious calculations. We recall what we already ate in the day. Likely, we think about a few meals that we had earlier in the week. Would we like to eat something similar or different? We map our social environment. With whom will we have dinner? When did we last eat with them? What did they eat earlier in the day? What was our last conversation with them about? Have we been on good terms, and how will our meal together affect our relationship? The list of questions that we process in a moment is staggering. We plan our meals not only according to physical need, but according to the complex social world around us. To understand this world, we fabricate stories. So, for example, I might think the following: “I would like to go out for sushi tonight because I haven’t had it in a few weeks. I know that John likes it, and since we haven’t spent much time together recently, it will be nice to have dinner at a restaurant.” My story doesn’t sound much like history, but I am thinking about the past nevertheless — even if it’s the recent past. And this is what history does. It tells us where we’ve come from and where we’re going. It gives structure to our experience. How and why we plan out our meals is something that we rarely think about. We simply do it, and we do it by reflecting on what came before. If we bear in mind that humans are the only animals that work in this way — to this extent — the act takes on more significance. Our historical sense shapes our daily routines to such a degree that we’re rarely cognizant of it.
Many scientists and philosophers believe that the level to which historical thinking shapes our humanity is unique to our species, both on a biological and on a social level. And, over the last several decades, studies have demonstrated that our ability to conceptualize our past is an essential feature of the human experience. At the forefront of this revolution in cognitive science has been Endel Tulving. In the 1980s, Tulving proposed the idea that the human sense of time is a central element of human consciousness. He called the concept “chronosthesia.” Some have popularized the idea by calling it “Mental Time Travel,” but one might also call it “historical consciousness.” Simply put, chronosthesia is the ability to situate ourselves in the past, present, and the future — through memory and imagination. In fact, it requires us to be self-conscious, imaginative, and intellectually flexible, which are all traits that seem to help distinguish humans from other animals. The general idea is straightforward, but it has profound implications for our understanding of human nature, memory, and cognition.
Tulving argues that humans have several types of memory. The first, procedural memory, is a non-conscious form of memory. Muscle memory is one form that it takes. When we do something enough — let’s say riding a bicycle or using a fork — the action becomes second nature. We weren’t born with the skill, but we’ve performed the action so many times that we don’t need to think about it. Musicians rely on procedural memory to become adept at their instruments and to train their voices. All animals use procedural memory to some extent. Male zebra finches, for example, learn songs from the their male parent. In fact, they have two types of song. The first is a mating song, directed at female finches. The second is a practice song, which finches use to improve their voices. Just like opera singers, the finches develop their muscle memory so that they can perform better. One of the most fascinating recent discoveries about procedural memory is that sections of the human brain actually grow the more we practice. Then, they shrink as we refine our skills. This is probably because we have to make lots of mistakes before we become proficient in anything. The expansion happens when the brain builds its neural networks, working hard to both perform the correct techniques and filter out mistakes. As we become more skilled, the brain no longer needs to filter as many mistakes and is able to contract again.
Unlike procedural memory, the second form of memory — semantic memory — is a conscious form of memory. It allows us to recall things, but it doesn’t necessarily provide a context. So, for example, we can remember that two is larger than one. In fact, we can perform all kinds of mathematical equations without the need for context. Likewise, we can remember basic relationships — for example, that a tree is a plant and not an animal. Semantic memory allows us to relate concepts and meanings, the building blocks of human knowledge. Put simply, semantic memory allows us to call up facts from our experience without reference to time or space. And, for many things, this is sufficient. To know that a tree is a plant does not require us to know where or when we saw a tree.
Semantic memory is a broad category that forms the basis for the more complex form of memory that Tulving calls episodic memory. It is this form of memory that has provided some of the greatest insights into human cognition over the past several decades. Where semantic memory allows us to recall facts, episodic memory orders those facts in their context. It helps us understand the temporal and spatial dimensions of our knowledge. This form of memory situates the things we know in the realm of our past experiences. It’s as if each of us has a built-in system of autobiography. So, for example, episodic memory helps us remember the events from our childhood in a linear sequence. Episodic memory is where our historical consciousness comes from. It is the story-making mechanism of our brain, and it gives order to our experience of time.
What is interesting about episodic memory is that it doesn’t seem to be distinct from another form of temporal reckoning — specifically, our ability to project into the future. We often hear historians say that we need to learn from the past so that we don’t repeat the same mistakes. It turns out that the human brain has evolved an analogous neurological function. Back in 1985, Tulving suggested that this might be the case. Multiple experiments have confirmed his hypothesis that the ability to remember past events determines our ability to imagine future events. Functional magnetic resonance imaging, or fMRI, has revealed that the regions of the brain that we use to remember are the same ones that we use to project into the future. In one experiment, doctors analyzed patients who had amnesia caused by damage to the hippocampus, a region of the brain crucial for temporal thinking. Unable to remember their pasts, they also had difficulty imagining commonplace future scenarios. It seems that our ability to mentally time travel — to remember our pasts and to imagine our futures — are biologically linked.
Historical consciousness is written into the very fibers of our brains. It is part of our evolutionary heritage — a key part. Without it, human culture would be impossible. Take human tool-making capacities as an example. Humans are certainly not the only creatures able to use tools. Chimpanzees are known to use sticks to go termite “fishing.” Scientists have even observed at least one group of chimpanzees using spears to hunt for other mammals. Female dolphins in Shark Bay, Western Australia have learned to use sponges to protect their rostrum, or “bottle nose,” when digging in the rocks and coral to dislodge fish. However, as early as 1.6 million years ago, homo erectus began using tools differently than other animals. How they used them was related to developments in their cognitive capabilities — and, notably their ability to think about the past to plan for the future.
Archaeologists have evidence of hominine-manufactured tools as old as 2.4 million years ago. Found in the Olduvai Gorge in what is modern-day Tanzania, the stone tools — known as Oldowan tools — are probably not the first tools used by hominins and their predecessors. But, they are the first tools found in the archaeological record. Used for scraping, chopping, and pounding, the stones were manufactured by flaking off a rock core’s edges with a hammer stone. The sharp flakes were then used for a variety of tasks. It is probable that to various extents migratory groups — homo habilis and homo ergaster — carried both stones and hammers with them to flake off cutting implements as needed. Roughly .8 million years later, homo erectus made further stone tool refinements. Acheulean tools, as they are known, require more skill and precision to make. They are bifacial, meaning that there are cutting surfaces on two sides. They often worked the edges more finely, and archaeologists suggest that there may have been some specialization in use. The tools served both a social and use function. Not only was it an efficient cutting implement, but the skill of the individual making a bifacial handaxe probably gave some status within their society. Recent evidence has shown that some Acheulean tools served no work function and may have existed for ritual use, to demonstrate status, or even to impress members of the opposite sex.
The tools found in the archaeological record suggest that the predecessors of modern humans eventually developed a modicum of historical consciousness. Tool creation and use, initially an ad hoc activity, became one that required foresight. They began carrying their equipment from place to place as they migrated. And, more sophisticated tools, such as bifacial handaxes, may have been fashioned in advance, suggesting that their owners were thinking ahead to future activities. This was not and is not the case with other animals, even those that do use tools. Neuroimaging studies of modern humans add another level to our understanding. It turns out that Oldowan flake and Acheulian handaxe production spark different parts of the brain. The latter requires a more complex set of processes suggesting that there was a relation between tool production, cognitive ability, and historical consciousness. The seemingly simple shift in tool production represents a key evolutionary moment for hominins.
Stone tools allowed them to extract more energy from their environment — whether through preparing vegetables, fruits, nuts, or meat. In the process of flaking stones, these toolmakers also found a method to create sparks by hand. Homo erectus and later homo sapiens would refine the method and begin experimenting with the tool of fire and extract even more energy from their food and environment. Increased caloric intake allowed brain sizes to expand — and a positive feedback loop emerged. Better planning provided more calories, and more calories allowed for more complexity in the brain. In turn, more intelligence led to more sophisticated planning. These advances also created the intellectual capacity to develop more complex languages and social learning. In approximately 2.4 million years — fewer than 150,000 generations — hominins moved from basic tool construction to long-distance trade and migration to mining to agriculture to large-scale civilization. The outcome was neither pre-determined nor linear, but the results are stunning. This success story of early hominins is due in large part to the capacity for historical consciousness.
 Jon Cohen, Almost Chimpanzee: Searching for What Makes Us Human, in Rainforests, Labs, Sanctuaries, and Zoos (Macmillan, 2010), 154.
 Amanda Reed et al., “Cortical Map Plasticity Improves Learning but Is Not Necessary for Improved Performance,” Neuron 70, no. 1 (April 14, 2011): 121-131; Jason Castro, “The Learning Brain Gets Bigger–Then Smaller: New studies map the changing landscape of neurons as the brain masters a task,” Scientific American (24 May 2011), http://www.scientificamerican.com/article.cfm?id=the-learning-brain-gets-bigger-then-smaller.
 Endel Tulving, “Memory and Consciousness,” Canadian Psychology/Psychologie canadienne 26, no. 1 (1985): 5.
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 Hassabis et al., “Patients with hippocampal amnesia cannot imagine new experiences.”
 Jill D. Pruetz and Paco Bertolani, “Savanna Chimpanzees, Pan troglodytes verus, Hunt with Tools,” Current Biology 17, no. 5 (March 2007): 412-417.
 Michael Krützen et al., “Cultural transmission of tool use in bottlenose dolphins,” Proceedings of the National Academy of Sciences of the United States of America 102, no. 25 (June 21, 2005): 8939 -8943.
 Marek Kohn, As We Know it: Coming to Terms with an Evolved Mind, new ed. (Granta Books, 2000).
 Thomas Suddendorf and Janie Busby, “Mental time travel in animals?,” Trends in Cognitive Sciences 7, no. 9 (September 2003): 5; T Suddendorf and M C Corballis, “Mental time travel and the evolution of the human mind,” Genetic, Social, and General Psychology Monographs 123, no. 2 (May 1997): 133-167; Thomas Suddendorf and Michael C Corballis, “The evolution of foresight: What is mental time travel, and is it unique to humans?,” The Behavioral and Brain Sciences 30, no. 3 (June 2007): 299-313; discussion 313-351.
 There is evidence that in experimental conditions, chimpanzees transport tools. See Thomas Suddendorf, “Foresight and Evolution of the Human Mind,” Science 312, no. 5776 (May 19, 2006): 1006 -1007.
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