Humans Are Animals, Too

  

Humans Are Animals, Too

For a significant duration, there has been an enduring debate in the realm of animal behavior and cognition. Two main factions have emerged: the exclusivists, who emphasize the distinctions between humans and other animals, and the inclusivists, who focus on the similarities between humans and the rest of the animal kingdom. This debate has ancient origins, with philosophers such as Aristotle and Descartes contending that humans possess unique higher-order cognitive abilities like rational thought and language, while thinkers like Voltaire, Charles Darwin, and David Hume argued that animals exhibit thought and reason, just like humans.

Bridging the gap between evolutionary biology and cognitive science, W. Tecumseh Fitch, a cognitive biologist from the University of Vienna, has stressed the importance of studying our more distant animal relatives to gain insights into human cognition. He conveyed this perspective during his keynote speech at the 2017 International Convention of Psychological Science in Vienna, emphasizing that both sides of the debate hold merit. He pointed out a simple biological fact: humans are, in essence, animals as well.

The foundation of human biology shares numerous fundamental elements with other life forms, from bacteria to daffodils, and our nervous system structure exhibits similarities with various animals, including insects, worms, and closer relatives like bonobos. However, each species retains its uniqueness.

Cognitive biologists like Fitch work to connect evolutionary biology (in the vein of Darwin) with the cognitive sciences (in the tradition of Noam Chomsky and B. F. Skinner). It's important to note that cognitive biology differs from evolutionary psychology, as it takes a broader approach encompassing a longer span of human evolution.

Cognitive biologists employ a "divide and conquer" or multicomponent approach to deconstruct complex traits, such as language or music, into their basic components. Some of these components may be shared among humans and other animals, while others may be unique to specific species. This approach allows for the construction of a phylogenetic tree to trace the evolutionary history of particular cognitive abilities based on the presence or absence of these components.

Humans share many traits with their closest relatives, the great apes, due to common ancestry. These shared traits include large brains, large body size, long lifespans, and extended childhoods. This phenomenon is called homology, where different species share characteristics inherited from a common ancestor. On the other hand, convergent evolution occurs when different species independently develop similar features, as exemplified by humans and birds independently evolving bipedalism.

Evolution is often characterized by circuitous routes, with adaptations arising and disappearing multiple times within a species. For instance, most humans and some other primates are trichromats, possessing color vision due to three different types of cone cells in their eyes. However, broadening the comparative perspective beyond mammals reveals that birds have tetrachromacy, featuring four different cones. Fish, reptiles, and amphibians also exhibit tetrachromacy, indicating that the common ancestor of all vertebrates likely possessed this trait. Primates, including some humans, reacquired partial color vision during their evolutionary history.

Tool use is another trait that has evolved independently in various animal clades, with examples like chimpanzees using tools for tasks such as termite fishing and nut cracking. This adaptation has multiple origins and pathways, raising questions about why and how it has evolved in distinct species.

Humans share many cognitive abilities with other species, including memory formation, categorization, basic emotions, planning, goal-setting, and rule learning. These nonverbal concepts likely paved the way for the development of language over millions of years of evolution. While humans possess language, its individual components are shared with other species, making the key distinction our ability to communicate complex thoughts.

Language's uniqueness in humans is not due to cognitive capacity but rather the ability to vocalize and control sounds. Primates like chimps and bonobos, while capable of learning signs or using keyboards, have limited control over vocalizations and sound imitation. This limitation is often attributed to the structure of their vocal anatomy, particularly the larynx. However, Fitch's research suggests that the vocal anatomy is not the primary factor, as it's observed in various mammals. Instead, the critical difference lies in the neural connections between the motor cortex and the vocal tract, which humans possess in a unique way.

While humans have these direct neural connections, other vocal-learning animals like bats, elephants, seals, cetaceans, and some birds have also evolved such connections. This enables researchers to test hypotheses about the evolution of vocal learning and language.

Syntax, the set of rules that govern sentence meaning, is central to language. Beyond spoken language, humans can use language in various forms, including sign language and writing, thanks to their advanced syntax. Apes, though they can learn and express many words through signs or keyboards, exhibit a limited level of syntax similar to a 2-year-old child. The ability to interpret hierarchical structures in language appears to be unique to humans.

Experimental studies with birds, such as pigeons and keas, have shown that more complex hierarchical syntax remains a human-specific trait. This suggests that humans have evolved a unique cognitive propensity for recognizing hierarchical structures within sequences. Fitch's dendrophilia hypothesis posits that humans' aptitude for syntax arises from their ability to interpret sequences as branching hierarchical structures. This cognitive leap is facilitated by an enhanced form of abstract memory that allows humans to track phrases even after they conclude, potentially aided by expanded neural structures like Broca's area.

In summary, W. Tecumseh Fitch's research emphasizes the value of comparative analysis across a wide range of species to understand the evolutionary history of cognitive abilities, including language and syntax, and to elucidate the unique features of human cognition. This approach provides valuable insights into the connections between evolutionary biology and cognitive science.