| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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Counterpoints in Science One's Sense of Self
Last April, the journal Science featured a group of articles entitled “Reflections on Self: Immunity and Beyond.” The editors recounted the Greek myth of Narcissus, who fell in love with his own reflection in a pool and drowned diving in after it. They saw this as a metaphor for the importance of being able to distinguish self from nonself. The immune system evolved to take on this task, to attack dangerous nonself invaders like viruses, bacteria, and parasites without inflicting undue damage on the self. Like our nation’s protective forces in the war against terror, the immune system deploys a remarkable array of surveillance techniques and weaponry, but like these forces it may not always be able to discriminate friend from foe, or stop an attack before it inflicts casualties. The more we have learned about self-recognition—within plants and animals, among individuals in colonies, and by the human brain—the more complicated it has proven to be. The immune system of vertebrate animals evolved primarily to detect molecular patterns produced by infectious agents. Detection triggers an immune response in which many types of cells and proteins attack the invaders.Normal body cells carry protein codes on their surfaces that identify them as friend, rather than foe. But if the cell is infected by a virus or transformed by a mutation, these identifiers may be missing or altered, and natural killer cells will go into action and liquidate that cell. Some pathogens are so sneaky, though, that they “steal” these molecular passwords to disguise themselves and escape destruction. Researcher Polly Matzinger from Brown University points out in the same issue of Science that there are still many unresolved questions about how the immune system discriminates between self and nonself. What happens, for instance, when the “self” changes through puberty, metamorphosis, pregnancy, and aging? Why aren’t the products of these changes attacked? Why do mammalian mothers not reject their fetuses, or attack their newly lactating breasts, which produce milk proteins that were not part of an earlier version of self? Why do we fail to reject tumors? Why do most of us escape getting autoimmune diseases like rheumatoid arthritis or multiple sclerosis, while a few individuals succumb? Matzinger believes that the immune system is concerned with damage as well as foreignness, and is called into action by alarm signals, such as heat-shock proteins and interferon, from injured tissues. She thinks that healthy fetuses, for example, are not rejected because they do not send alarm signals. Transplants, however, which in some ways resemble fetuses, cannot be performed without surgical damage, which sets off the alarms that often result in rejection. Most of the immunosuppressive drugs used to prevent transplant rejection work by blocking the body’s innate alarm systems, especially the lymphocytes that attack foreign cells. All animals, even insects, have pattern recognition systems that distinguish nonself. It was a surprise, then, tofind that in many plants, the recognition systems focus on identifying and attacking self, while nonself is ignored. Most plants have both male and female sex organs. Though some plants do just fine as self-pollinators, self-mating generally is deleterious to offspring, and evolution has devised ways of preventing individual plants from fertilizing themselves. Self-incompatibility systems have evolved independently in the crucifer, poppy, tobacco, rose, and snapdragon families. According to plant biologist June Nasrallah, also writing in Science, when pollen, the male sperm of a plant, tries to burrow toward the female ovule of that same plant, the alert recognition system says, “No, no,” and blocks its passage. The agents of this blockage are small proteins and enzymes remotely related to the immune defenses of animals. To evolutionary biologists, the self is the individual, selected to nourish itself, to protect itself, and especially to reproduce itself. Some individuals are simple prokaryotic cells like bacteria, others are eukaryotic cells like yeast, and still others are multicellular populations like plants and animals. Each new level of complexity acquires individuality or selfhood when the constituent cells and organs merge their separate identities and work together as an entity. The social insects, which include termites, ants, bees, and wasps, take the progression one step further, as described in Science by evolutionary biologists David C. Queller and Joan E. Strassmann of Rice University. Colonies of social insects are so tightly integrated that they seem to function as single superorganisms, at a new level of self. When the single reproducing queen is threatened, the workers protect her with suicidal assaults, much as the immune system assaults invaders. Most social insects have well-defined colony barriers with few entrances, and they attack foreigners who breach those boundaries. However, the superorganism sends out pieces of itself to find food, so it needs to recognize and readmit those pieces without admitting intruders. These superorganisms lack the genetic markers that distinguish self from nonself in vertebrates, so the members of each colony actually learn the cues that differentiate their own colony from others. An individual learns the odors of colony-mates and nest material and uses these identifiers for later reference. Ants and bees, even though they act like superorganisms, don’t spend a lot of time contemplating the nature of the self or why they have come to exist on this planet. The burden of metaphysical reflection seems to be borne solely by members of our own species, who have spawned origin myths, religions, and endless speculations in attempting to understand these fundamental questions. Mathematician and philosopher René Descartes famously declared, “Cogito ergo sum” (I think therefore I am), neatly defining selfhood, consciousness, and existence in three Latin words. Philosopher Patricia S. Churchland, however, finds Descartes’ utterance unsatisfactory because he left out the physical body. Conscious thoughts, she points out, are activities of the physical brain, and there is no experience of the “self” as a distinct thing apart from the body. The self thus turns out to be identifiable not with a nonphysical soul, as Descartes and many others believed, but with the representational capacities of the physical brain. Churchland writes in Science that the brain arose as an evolutionary solution for coordinating and regulating inner-body signals. Some brain networks control inner states of the body, while others represent perceptions of the external world. At present, efforts to define the self are shifting from the mystical and philosophical realms into the province of the brain and cognitive sciences. Great progress has already been made in understanding color perception, autobiographical memory, the emotions, decision-making, sleep and dreaming, and consciousness. Some amnesiacs with hippocampal lesions, for instance, are unable to acquire new knowledge and have lost all autobiographical information. One such patient, described by A.R. Damasio, a well-known neurologist, lives in a 40-second time-bin, not remembering the past or foreseeing the future. But he is self-aware, self-controlled in social situations, talks, and experiences happiness and sympathy for others. We see the slow emergence and elaboration of self-awareness and self-identification in children and the tragic fading of these capacities in aging patients with dementia. A schizophrenic may suffer deep confusion about self-nonself boundaries, sometimes claiming that his own sensations belong to someone else or exist outside himself. A patient with a lesion in her right parietal cortex, resulting in loss of sensation and movement on the left side, may deny that the left limbs are hers and try to throw them out of bed as alien objects. Though all living organisms seem to have molecular recognition systems that distinguish self from nonself, and a large number are equipped with remarkably complex brains, conscious awareness of self is extraordinarily rare, limited so far as we know to humans, their close relatives the great apes, and cetaceans. Chimpanzees (but not monkeys) and dolphins can recognize themselves in a mirror. The human sense of self is largely psychological, consisting of qualities an individual considers important or identifies with, such as strength, height, intelligence, ethnicity, profession, or social relationships. One’s-self is indeed a much more layered affair than the simple, separate Person Walt Whitman sang of. It is a genetic blueprint of three billion base pairs, produced by four billion years of evolution, manifested as a structured organism of several trillion coordinated cells. It contains incredibly elaborate and sophisticated immune and neurological circuits that define, protect, and defend it against internal and external forces. And it is, to a unique degree, a self that has a sense of itself. We must be careful not to drown in narcissism over our gift of awareness, and we may take issue with Descartes’ three-word summing-up, but we can’t help empathizing with Whitman’s ringing manifesto, “I celebrate myself!”
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"One’s-self
I sing—a simple, separate Person,” begins Walt Whitman’s great poem “Leaves
of Grass.” One’s self may seem like a simple notion, but philosophers,
psychologists, and biological scientists have been wrestling with its
meaning for centuries.