One of the traditional lines of metaphysical inquiry entail drawing lines of demarcation between various classes of entities and/or systems. From an evolutionary standpoint, one of the most venerable lines on inquiry involves the line of demarcation between the various species of living things, especially between humans and animals.
Historically, one of the most common methods for drawing these lines has been to construct hierarchies. In human affairs, these hierarchies have always been used to justify our behavior toward different classes of entities. The most familiar hierarchies draw lines of demarcation between: living and non-living things, human and non-humans, males and females, and a wide variety of lines between human groups, such as: tribes, religions, races, social classes, and overly-zealous fans of competing high school football teams. As a moral mechanism, one’s place within a hierarchy determines how you are treated by those situated both above and below you. (It’s great when you’re on the top of a hierarchy and not-so-great when you’re on bottom!)
One major bone of philosophical contention here is whether these hierarchies are “real” in the sense that they actually correspond to an external natural order, whether hierarchies are “real” in the sense that they correspond to internal brain programming, or whether they are “real” in the sense that they are “social constructions” that mask and enforce natural or unnatural relationships of power.
In the history of human inquiry, the most replicated hierarchical organizational schemes are variations of the “Great Chain of Being,” a longstanding line of inquiry that hierarchically arranges the various kinds of living organisms. There are many different ways to organize these hierarchies. We can set them up as food chains (who-eats-who). We can set them up based on degree of complexity from small, relatively simple microscopic organisms (bacteria) to large, more complex, macroscopic animals (whales and humans) etc. Religions often set up hierarchies based on proximity to God. Germs occupy the lower rungs of the hierarchy and are situated a long way from their creator! Therefore, don’t feel guilty when you take your antibiotics.
As stated earlier, many religions trace the origin of the living and non-living aspects of the universe to a deliberate act of creation by a God, which in turn affects their hierarchical taxonomies. In the Western theistic tradition, God the creator is endowed with superlative attributes such as: omnipotence, omniscience, omnipresence, and goodness. God, therefore, stands at the top of the Great Chain of Being, which sets us up for theological inquiry into the precise relationships between God and various living and non-living components of the universe. Non-living systems, or things, are usually situated at the bottom of the Great Chain. Within the class of non-living things God is sometimes associated with systemic order of those things, such as the motion of the planets. All of this raises questions concerning the line of demarcation between non-living and living things. There are, however, many pantheistic and deistic non-Western religions that are less anthropocentric and less committed to these rigid hierarchies. Some religions even situate animals and plants on an even plane, or above us!
a lot of high-ranking cows. India
Animal psychology, according to seventeenth-century philosopher, Rene Descartes’ is straightforward and obviously amenable to the prevailing Newtonian methodology. He argued that animals are simply machinelike material entities, or automatons, that lack mind or consciousness. Their behavior, therefore, can be explained entirely in terms of the Newtonian laws that govern their material bodies. So their biological existence is programmed by innate reflexive neurological activity. Logically, it followed that if animals are strictly finite, machinelike, temporal creatures, it’s because they lack an eternal soul.
Obviously, the bodies of human beings resemble the bodies of animals, and therefore, are also subject to Newtonian analysis, and can be reduced to the interaction of material entities and processes at the microcosmic level. However, consciousness itself, according to the Cartesian tradition, cannot be entirely reduced to those material entities and processes. Bodies are one thing and minds are something else. Hence, Descartes invoked a pluralistic, mind-body ontology, which had been a longstanding staple of Western philosophy and theology. It is predicated on the ontological reality of both material systems and mental systems. Material systems change via material causes and spiritual or mental systems change via spiritual or mental causes.
Descartes argued that all living things are complex machines and that although human beings have machinelike attributes, we are qualitatively different from the rest of God’s creation. The presence of an eternal soul (or mind or consciousness) was invoked to draw that line. The soul, being Godlike, therefore, elevates human beings to the upper rungs of the Great Chain, just below angels. Human males are usually situated above women and children, but below angels. Just below human beings we have various classes of animals and then plants, which are just above non-living things. (Americans and Europeans seem to rank their cats and dogs well above third-world humans on the Great Chain. Most of our pets eat a lot better than most non-Western humans.) But contemporary biological evolution casts serious doubt on the veracity of these traditional hierarchies and the hard lines of demarcation that they seem to imply.
Today, evolutionary biologists argue that in order to explain the emergence of the human species body (including our large brains and distinctive feelings, thoughts, percepts, and behavior) we must conduct genealogical research on our closest evolutionary forbears. According to long-standing orthodoxy, the human species Homo sapiens are genealogically descended from the primate order. More recent discoveries have divided the various species of primates into two main branches the Old World Primates, which evolved into Old World Monkeys (Baboons and Macaques) and the Great Apes (Chimpanzees, Bonobos, Gorillas, and Orangutans). About 35 million years ago, New World Monkeys (Capuchins, Muriquis, and Squirrel Monkeys) branched off of the Old World Primates.
For many years, scientists struggled to scientifically establish the precise genealogy of the "Great Apes," especially the hominids, which eventually evolved into modern humans. The sociopolitical problem has been that evolutionary biology postulates the interrelatedness of species. This belief conflicts with longstanding non-scientific religious beliefs. For monists, this can pose a problem. If you believe that genetic theory is approximately true, then, (logically at least) you’ll have a hard time rejecting the idea that all living things are genealogically related and that humans are closely related to chimpanzees. In short, the scientific evidence in support of biological evolution is about as overwhelming as it can get: but still far short of mathematical certainty!
In 1984, Sibley and Ahlquist developed a procedure called DNA hybridization. It involved extracting single strands of DNA from the blood of two different species, then allowing the nucleotide sequences to bind or "zip" together, thus creating a hybrid. When heated, the strands of DNA in the zipper separated. The greater the melting temperature required to achieve separation, the closer the relationship between the species within the hybrid.
When they tested the Great Apes they concluded that orangutans first diverged from the hominid line about 10-16 million years ago and that gorillas, bonobos, and humans all evolved from a common ancestor about 5 million years ago. Chimpanzees branched off of the bonobo lineage about two million years ago and are more closely related, genetically, than to any other primate species. When the testing was over, it turned out that we humans are indeed more closely related to chimpanzees than we are to gorillas or orangutans, and that chimpanzees are more closely related to humans than they are gorillas. As Jared Diamond put it, we are the "Third Chimpanzee." Imagine how disconcerting that discovery must have been. For centuries, theologians, philosophers, and scientists have defended that inviolable line of demarcation between man and animal. Predictably, many scientific and non-scientific inquirers reject either their methodology or conclusions. Let the ad hoc explanations begin!
According to modern evolutionary theory, human beings actually evolved rather quickly in comparison to what we know about the evolution of other species. During this relatively short 5 million year interval, we evolved from a "Rainforest Ape" to "Woodland Ape," and through several pre-human species including (Australopithecus (4 million years ago), and Homo erectus (1.7 million years ago). According to Wrangham and Peterson, we are only about 150,000-230,000 years old.
The main difference between modern humans and other primates seem to be the relative size of our brains and our cerebral cortex. The average human brain today weighs about 3 pounds and contains about 100 billion nerve cells, called neurons. In humans, that cerebral cortex contains about 30 billion neurons and one million billion connections, or synapses. Brain scientists like to argue that the human brain is the most complex system on earth. Actually the higher level systems that “emerge” out of our brain activity, such as popular culture and market economies, are much more complex. Remember, we’re dealing with open-systems!
Although the human brain has evolved slowly over millions of years, the idea of brain localization theory has evolved much more rapidly. Historians can explore how contemporary brain theory evolved out of earlier intellectual systems by observing cultural artifacts such as old scientific books and articles on neurology. When future intellectual historians look back on the history of biological inquiry, they will be hard pressed to explain the persistent intellectual, sociopolitical, and economic conflicts that arise out of our current beliefs about the relationships between animals and humans.
At this point I must reiterate that our evolving descriptive beliefs concerning the status of animals in relationship to humans influence our evolving prescriptive moral beliefs concerning the borders of the moral universe. Today, many animal rights advocates argue that it is immoral to treat sentient and/or non-sentient animals as things, property, or resources. This animal rights movement, therefore, seeks to break down and reorder these longstanding anthropocentric hierarchies. But how does the possession of something that resembles a cerebral cortex signify membership in the moral universe? Why is extending the boundaries of that universe to include mammals (mammalpocentrism?) morally superior to anthropocentrism?