(continued from Part 1)
As some scientists have collected more evidence about the evolutionary development of chronesthesia in humans, others have begun to ask similar questions about other species. Why did only certain hominins acquire a sophisticated historical consciousness some time between 2.4 and 1.6 million years ago? Is it possible that other animals also have the capacity to think historically — to mentally time travel? In many ways, these scientific questions are a variant of basic metaphysical questions that humans have been asking throughout their history. Who are we? What is our place in nature? What makes us different from the other animals that we come into contact with? Our big philosophical and scientific questions emerged out of our ability to reflect about ourselves, the world in which we live, our history, and our future. They are the result of our evolutionary heritage.
For the last several thousand years, in Europe at least, the answer to humanity’s big questions have come from anthropocentric philosophical conceptions. We are self-conscious, rational creatures, and this is the fundamental difference between humans and animals. We can see it in the philosophies of the ancient Greeks and Romans. In Athens, Socrates and his followers argued that what distinguished humans from animals was their capacity to reason. Aristotle, the teacher of Alexander the Great, was one of the most sophisticated proponents of this idea and became widely influential for the next two thousand years. Most Christian philosophers agreed with Aristotle, subscribing to the basic argument that humans differed most substantially from animals because of their rational minds — even if they also claimed that humans had an eternal soul and were inherently sinful. Augustine of Hippo, an influential early Christian thinker, argued that humanity’s sinful nature should make them suspicious of any knowledge not derived from the Christian scriptures. Nevertheless, he conceded that humans were rational creatures and that their reason could lead to truths not clarified by their religious texts. At the University of Paris in the thirteenth century, Thomas Aquinas would be more optimistic. He claimed that independent human reason could, in most cases, lead to the same truths as Christian scripture. Unsurprisingly, he also argued that the rational soul was a uniquely human trait. He went so far as to claim that animals were akin to machines.
The seventeenth-century French philosopher René Descartes would disagree with his predecessors on many things, but he would agree on the simple fact that what separated human from animal was reason. Like Aquinas, Descartes argued that only humans had rational souls. No doubt inspired by the sophisticated machines of his day, he claimed that without reason, animals were nothing more than automatons — mechanical devices that operated on their own. Renaissance philosophers, princes, and commoners alike were fascinated by these mechanical marvels. Technicians, such as Salomon de Caus, made careers out of designing mechanical devices for the gardens of aristocrats and kings. Traveler that he was, Descartes saw automata in royal gardens throughout Europe. Churches abounded with these machines, embedded in complicated clocks and organs. He was able to see devices similar to Juanelo Turriano’s automaton figure of a monk, which walked, prayed, and kissed the rosary.
Mechanical humans, animals, and mythological beasts walked, talked, and even played tricks on unsuspecting visitors.
Descartes concluded that the earth’s animals were little different than a clock, and the same could be said of the human body. He imagined levers, pulleys, and hydraulic systems working away inside the human machine. He could look to the mechanical arms, hands, and legs designed by the sixteenth-century French battlefield surgeon Ambroise Paré and imagine that these prosthetics were little different from biological appendages. Human and animal bodies were alive, but being alive and being a rational creature were two different things. To be rational, one needed a soul, and only humans had souls. For Descartes, the soul was connected via the pineal gland to the body, itself nothing more than a complex machine.
Descartes represents a shift in thought about human nature that began in the seventeenth century, but by the early nineteenth century, most European philosophers and scientists had not abandoned the idea that humans had a soul. They were, however, increasingly willing to question the primacy of human reason and imagine that humanity was driven by animal passions, desires, and instincts. Then, another dramatic shift occurred in the study of humanity: evolutionary biology.
For millennia, the dominant view of humanity in Europe was that human nature was static. Whether one argued that humans were driven by a rational soul or by their physical desires, the general conception was that they had been and always would be that way. This was because both the Graeco-Roman and Christian argued for an artisan-creator who formed the first humans whole and complete. Evolutionary biology changed everything. After the work of Jean-Baptiste Lamarck, Charles Darwin and Alfred Russel Wallace, whose work became the foundation of modern evolutionary theory, human nature was no longer static. Humans evolved along with the rest of the animal kingdom. Rationality, like other adaptations, was the consequence of chance mutations. For many people, there was a startling implication to this insight: philosophy could not provide a line dividing the human from the animal kingdom. The age-old metaphysics of human nature would have to be rethought to account for change over time — and more importantly to distinguish once again what, if anything, made humans different from animals. The answer wouldn’t be found through philosophical speculation. It would have to be found through empirical science.
Darwin recognized these facts, but rather than see them as a problem, he saw the opportunity to re-imagine humanity’s connection to the natural world. Throughout his 1871 work, Descent of Man, Darwin argued for the similarities in human and animal thinking — from emotions of sympathy, joy, and anger to rationality, abstract thought, and language. Humans and animals, especially the “higher apes” as he called them, showed differences of degree rather than kind. In dogs, he saw the ability to reason and overcome fixed habits. He noted the use of tools among apes and elephants. Parrots not only had their own language, but were able to learn, understand, and articulate human languages — at least at a rudimentary level.
In the century that followed, scientists largely confirmed Darwin’s observations with empirical evidence. African Gray Parrots, bees, humpback whales, dolphins, and apes all practice some form of communication with members of their group — and, in the cases of parrots, dolphins, and apes with humans as well. Experiments with crows reveal that they can distinguish one human from another. They recognize friend from foe and communicate with other crows about human individuals. A person who has treated one crow poorly will find that other crows in the area react to them with hostility — flying above them, squawking and screaming. Scientists have also observed abstract thought in a number of species including dogs, apes, and crows. New Caledonian Crows, for instance, are able to use tools to solve puzzles that require a degree of abstract causal reasoning.
In other words, they seem to have the capacity to understand cause and consequence.
Nineteenth-century evolutionary theory suggested that humans were simply one branch of the animal kingdom. This made the big philosophical questions about existence much more complex. Falling back on the idea that humans were fundamentally different from other creatures was implausible. Since then, scientific studies of animal language, abstraction, and causal reasoning have shown that the difference between humans and animals — even as far as consciousness is concerned — is probably a matter of degree rather than form. Nevertheless, when it comes to that core component of human nature — historical consciousness — the degree is quite substantial. To understand how it functions and its significance for the history of humanity, we have to see how biology and culture work together.
 Augustine of Hippo, City of God, ch. 11; On Christian Doctrine, chapters 31-39.
 Thomas Aquinas, Summa Theologica, Prima Secundæ Partis, Qu. 13, Art. 2, Reply obj. 3; Derek J. de Solla Price, “Automata and the Origins of Mechanism and Mechanistic Philosophy,” Technology and Culture 5, no. 1 (1964): 19; Jessica Riskin, “Machines in the Garden,” Republics of Letters: A Journal for the Study of Knowledge, Politics, and the Arts 1, no. 2 (April 3, 2010), http://rofl.stanford.edu/node/59.
 Attributed to Juanelo Turriano. Automaton figure of a monk. South Germany or Spain, ca. 1560. h: 15 inches. National Museum of American History, Smithsonian Institution, Washington, D.C.
 John M. Marzluff et al., “Lasting recognition of threatening people by wild American crows,” Animal Behaviour 79, no. 3 (March 2010): 699-707; Heather N. Cornell, John M. Marzluff, and Shannon Pecoraro, “Social learning spreads knowledge about dangerous humans among American crows,” Proceedings of the Royal Society B: Biological Sciences (June 29, 2011).
 A.H Taylor et al., “Do New Caledonian crows solve physical problems through causal reasoning?,” Proceedings of the Royal Society B: Biological Sciences 276, no. 1655 (January 22, 2009): 247 -254.
 Nicola S. Clayton, Timothy J. Bussey, and Anthony Dickinson, “Can animals recall the past and plan for the future?,” Nat Rev Neurosci 4, no. 8 (2003): 685-691; N. J Emery and N. S Clayton, “The mentality of crows: convergent evolution of intelligence in corvids and apes,” Science 306, no. 5703 (2004): 1903; C. R Raby et al., “Planning for the future by western scrub-jays,” Nature 445, no. 7130 (2007): 919–921. Cf. Suddendorf and Corballis, “Mental time travel and the evolution of the human mind”; Suddendorf and Busby, “Mental time travel in animals?”.