I. Why do we want to think humans are different?

Humans have the propensity to place things into categories (i.e., good vs. bad, full vs. empty, black vs. white), which can directly shape how we view the world. Since categorization shapes our actions, it is important to evaluate their validity and distinctness and the degree to which one category blurs into the next. One categorization that has intrigued scholars for centuries is that of humans versus nonhuman animals. We often put humans on a pedestal, as unique and superior to all other animals: one of a kind; unlike any other animal. For example, in the 17th century, Rene Descartes stated that only people were creatures of reason, linked to the mind of God, while animals were merely machines made of flesh. His follower Nicolas Malebranche went on to say that animals “eat without pleasure, cry without pain, grow without knowing it: they desire nothing, fear nothing, know nothing.” Today Descartes’s and Malebranche’s statements may seem extreme and wrong (Call, 2006), but they clearly reflect the propensity to see animals and humans as very different and humans as superior. 

The view of humans and animals has changed since the 17th century (Fuentes, 2018; Marks, 2016; Van Schaik, 2016), thus these categories need to be reevaluated. Other categorizations have changed dramatically over time, with very positive effects on human societies. When the U.S. Declaration of Independence and Constitution was written, “only white male property holders [were] deemed adequately endowed to be included in the category of personhood” (US 1776). This is no longer the definition of personhood. In fact, the question of whether great apes warrant being accorded personhood is generating much academic interest today (Kurki and Pietrzykowski, 2017; Shyam, 2015; Wise, 2014). 

A second reason to reevaluate the human/animal distinction is that many of our previous criteria for human uniqueness have proved wrong. Thomas Carlyle (1833) stated that “Man is a tool-using animal. Without tools he is nothing, with tools he is all” (Carlyle, 1833). This definition of “Man the Tool Maker” was largely viewed as true until the 1960s, when Jane Goodall’s observations of chimpanzees (Pan troglodytes) using tools to extract termites from their mounds (with the help of publicity from National Geographic) eventually invalidated Carlyle’s definition. It had taken well over a century (Goodall, 1986; Goodall, 1964). Prior to the Goodall findings, there had already been considerable evidence, largely ignored, that the definition was flawed. For example, in 1925 Köhler reported a series of simple experiments that clearly demonstrated chimpanzees could use tools and even cooperate in tool use to obtain food rewards. The chimpanzees would pile boxes one on top of another and then use sticks (even putting two sticks together) to reach a food reward hung high above their heads. Several primate species have now been shown to be habitual tool users, some maintaining tool-using cultures for hundreds of generations (Haslam et al., 2017). 

Today we know that tools are also used by many non-primate species such as elephants (Hart and Hart, 1994), Caledonia crows (van Casteren, 2017), African grey parrots (Pepperberg, 2004), sea otters (Hall and Schaller, 1964; Fujii et al., 2014), rodents (Nagano and Aoyama, 2017), octopuses (Finn et al., 2009), and some fish (Bernardi, 2012). 

A similar failed criterion had been put forward in 1891 by Sir William Osler, who stated: “A desire to take medicine is, perhaps, the great feature which distinguishes man from other animals.” The subsequent extensive documentation of medicinal plant use by chimpanzees and other primates opened the flood gates for research in this area (Huffman, 1997; Huffman, 2007), leading to examples of medicine use not only by other mammals (e.g., elephants, bears, civets, coatis, porcupines), but also birds (e.g., snow geese, finches, raptors) and insects (e.g., bumble bees, ants, butterflies) (Engel, 2002; Huffman, 2007). 

Chu (2014) suggested that humans are unique in their ability to build complex structures. A number of authors have since echoed this (Fuentes, 2017; Marks, 2015) despite the evidence of complex living constructions by animals such as beavers (Castor canadensis), birds, bees and wasps (Doucet et al., 1994; Hansell, 2000; Hepburn et al., 2016). Termite mounds are remarkable structures with specific areas built for different purposes, elaborate features for draining water and cooling the mound, and even gardens to cultivate fungi as a source of food and medicine (Darlington, 1985; Korb, 2003; Korb, 2010). 

These and many other such claims about putative defining differences between humans and animals span from 1833 to 2014 have proved wrong. Yet the desire to see humans as unique still remains. Is this a valid scientific question? One of the distinctive features of science is hypothesis testing (Cartmill, 1990; Popper, 1968). If hypotheses about human uniqueness repeatedly prove to be wrong for one trait after another, does this not imply that the hypothesis itself is wrong? We can keep resurrecting the hypothesis with new traits not yet considered, but to what end? 

Evolutionary theory is a widely accepted explanation for the diversity of life on the planet. If uniqueness were intended to mean humans are one of a kind, unlike anything else, this would contradict evolution[…]

 

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This article has appeared in the journal Animal Sentience, a peer-reviewed journal on animal cognition and feeling. It has been made open access, free for all, by WellBeing International and deposited in the WBI Studies Repository. DOI: 10.51291/2377-7478.1358

Originally published in Animal Sentience 23(1), 2018.

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