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For some years now, I have explored the connection between animals and humans and its enormous impact on the evolution of our species. For example, many scholars believe that the invention of language was spurred by the adaptive value of collecting detailed information and sharing it with others in our group. The classic example is the elder who remembers from his or her childhood where there are deeper water holes and leads the group to them in times of drought.
The catch with tracing the origin of language is that words (much less syntax and grammar) don't fossilize, so it is very hard to pin down exactly when this amazing ability first occurred. Anatomists have struggled in vain to identify traces on skulls that would signal the onset of language.
In 1991, William Noble and Iain Davidson suggested a different, clever way to recognize the origin of language.
"The property that most distinguishes language from other communication systems," they wrote, "is that its signs are symbolic. All communicative systems are collections of gestures, whether vocal, manual, or physical; these gestures are signs and they convey meanings." And they added, the relationship between the sign or gesture and the thing to which it refers is arbitrary–symbolic–and is recognized as arbitrary by those who use it. Thus, whether you say dog or chien or Fido really doesn't matter as long as the speaker and the listener agree on meaning.
Basically, language has three key attributes. First, it is about something; there is a topic that is the subject of communication. Second, information about the topic is conveyed through symbols. Third, a vocabulary of symbols must be shared by the speaker and the intended audience if communication is to occur.
Searching the fossil and archaeological record for the first evidence of symbols, Noble and Davidson identified the earliest symbols as being cave art–exquisite animal sculptures–32,000 years old. Since Noble and Davidson's first wrote their seminal article, objects have been discovered that place symbolic behavior earlier than 100,000 years ago. For example, deliberately pierced shells that were apparently strung as necklaces or bracelets are now known from Israel and Algeria at about 135,000 years ago. These objects of personal adornment are like tattoos, gang colors, school t-shirts, some hairdos, or badges: symbolic ways of proclaiming membership in a particular group. Decoding what that group was 135,000 years ago is almost impossible. Similarly, Blombos Cave, a remarkable site in South Africa, has yielded nineteen pieces of ochre carved in geometric patterns from between 77,000 and 100,000 years ago. What the patterns mean is as yet undeciphered (and may remain so); that the patterns had meaning is perfectly clear. The frustration lies in our ability to find such early symbols coupled with our inability to understand them.
The earliest symbols we can decipher are only about 40,000 years old. They are figurative prehistoric artworks like the cave paintings and engravings from places like Chauvet Cave, the subject of the recent film "Cave of Forgotten Dreams".
These figurative images are overwhelmingly of animals; the representations are intensely detailed and realistic, rich in information. I find it significant that these images do not depict landscapes, give directions for making tools or shelters or fires, or indicate where water or outcrops of useful rock can be found. They very rarely depict people. To me, their content reveals that information about animals was more vitally important than these other topics and transmitting that information to others gave an immense advantage to those with language. This is an important part of what I have called the "animal connection" and demonstrates one way in which being connected to animals had a formative influence on human evolution.
Now we can trace the influence of the animal connection on human evolution still further back in time than language, to visual perception. New findings by a team of neurobiologists provide strong support for the idea that the connection between humans and animals is very fundamental, very important, and very heritable.
Florian Mormann from the California Institute of Technology and colleagues conducted a simple study on 41 epileptic patients who had intractable seizures. The subjects were undergoing electrophysiological monitoring to determine which parts of their brains were involved in seizures. Electrodes were implanted in three areas of the brain: the amygdala, the hippocampus, and the entorhinal cortex. All three regions are part of the limbic system which processes and integrates events of emotional importance into long-term memory. The limbic system focuses attention on important aspects of the environment, prepares parts of the body for action when appropriate, and motivates bodily expression of important information.
During each experimental session, subjects viewed approximately 100 assorted images on a screen while the responses of neurons in these three areas was recorded. The images were projected randomly and showed people's faces, animals, landmarks, or objects. The people were often celebrities whose faces would be known to subjects. Animals shown included mammals, birds, insects, and reptiles, but none of the animals were personally known to the subjects. Some were domesticated animals and others were wild. Landmarks included famous sites - like the Egyptian pyramids or the Colosseum in Rome - and unknown scenes. Objects included cars, tools, and food items. The readout from the implanted electrodes indicated which regions of the brain responded to which particular stimuli.
The amygdala showed a strikingly different response pattern from the other parts of the brain. Neurons in the right amygdala responded preferentially to pictures of animals and responded more markedly to such images. The left amygdala, hippocampus, and entorhinal complex showed no such preferences. The differences were very significant statistically.
After checking for and eliminating many potential confounding factors, Mormann and colleagues concluded, "[The right] amygdala is specialized for processing visual information about animals." They explain that this function is localized to the right side because the entire right hemisphere of the brain has is specialized for responding to unexpected and biologically important stimuli.
Why would the right amygdala be hard-wired for responding to, focusing on, and remembering visual information about animals?
My answer is that this functional specialization in the brain helped our early ancestors survive their anomalous position as predators-without-bodily-equipment long before the invention of language. Unlike other mammalian predators, our ancestors did not evolve strong forelimbs, grasping claws, slicing teeth, speed, or an enhanced sense of smell for capturing animals. Our ancestors took an evolutionary short-cut 2.6 million years ago and invented stone tools. With those tools, they were able to obtain meat, fat, marrow, and hide from prey that they had never been able to take before. Abundant cutmarks on fossil bones starting at 2.6 million years ago show that our ancestors quickly became highly effective hunters, even though they had none of the bodily equipment of true carnivores.
By being predators-without-equipment, our ancestors came under evolutionary pressure to pay close attention both to the real carnivores, who competed for prey and wouldn't balk at eating our ancestors, and their own potential prey. Accumulating visual information about the behavior of both sorts of animals became key to survival.
The work by Mormann and his colleagues provides the electrophysiological information that explains the results of another, early study, which focused on behavior. In a set of experiments involving the ability to detect visual changes, Joshua New, Leda Cosmides, and John Tooby exposed subjects to a pair of rapidly changing, complex images of natural scenes with a single alteration (a format known as a change detection study). They measured how quickly people were able to spot the change according to the category of the item that changed. Subjects detected changes in animals and other humans faster and more reliably than in stationary objects (tools, plants) or inanimate objects that are capable of movement (vehicles).
New and colleagues argued that observing changes in vehicle positions is a more pertinent survival skill among the subjects they tested than observing animals, since the subjects lived in urban environments. Yet, despite a lifetime of learning to watch out for moving cars, the subjects were more sensitive to changes in the position of humans or animals than vehicles.
This team concluded that the visual monitoring system is equipped with "ancestrally-derived selection criteria" - a special sensitivity to animals and people -- that "appears well designed for solving an ancient adaptive problem: detecting the presence of human and non-human animals and monitoring them for changes in their state and location." In short, they suggested that the sensitivity to visual information about the position of people and animals was an ancient one based on ancient needs of our species.
Both behaviorally (the change detection study) and electrophysiologically (the recent study), there is very strong evidence that a specific part of the brain is unusually sensitive to visual information about animals. We are hard-wired to pay attention to animals. This enhanced the survival of our lineage so significantly that a part of the brain was actually specialized to collect and respond to animal information.
Did you inherit a love of cats from your mother? Maybe, maybe not. But consciously or unconsciously, you did inherit from your ancestral mother a special ability to gather information about the animals around you.
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Readers can find more detailed information in the references below.
Mormann, Florian, Dubois, Julien, Kornblith, Simon, Milosavljevic, Milica, Cerf, Moran, Ison, Matias, Tsuchiya, Naotsugu, Kraskov, Alexander, Quian Quiroga, Rodrigo, Adolphs, Ralph, Fried, Itzhak, & Koch, Christof. 2011 "A category-specific response to animals in the right human amygdala". Nature Neuroscience 28 August 2011. doi:10.1038/nn.2899.
New, Joshua, Cosmides, Leda, and Tooby, John. 2007. "Category-specific attention for animals reflects ancestral priorities, not expertise." Proceedings of the National Academy of Science USA 104 (42): 16598-16603.
Shipman, Pat. 2011. THE ANIMAL CONNECTION, W.W. Norton & Co.
___________ 2011 "How Animals Shaped Our Minds." New Scientist 210: 32-37. ___________ 2010. The Animal Connection and Human Evolution. Current Anthropology 51(4): 519-32.
