Consciousness, sentience, and self-awareness are among the most contentious topics in biology, as well as in popular culture. In the past, it was commonly assumed by eminent philosophers that only humans were conscious and sentient, and no other animals, let alone non-animalian organisms, were. Additionally, even now, it is commonly believed that even some humans younger than a certain age, such as in the prenatal stages of life, are not capable of being in possession of these qualities. But a mass of scientific research, welling up to a profound crescendo which cannot be ignored, has been accumulating over the years that contradicts these assertions. No longer can we claim, while still remaining on solidly grounded scientific footing, that only postnatal Homo sapiens are conscious, sentient biological entities. In fact, one of the core assumptions accepted even by many in the scientific community now, that a brain, or, at the very least, a nervous system composed of neuronal cells, is necessary for consciousness, sentience, and self-awareness has now started to be persuasively challenged by the evidence. This is what is the primary focus of this present article.
Firstly, we need to define these terms. Consciousness can be defined as an awareness of one's surroundings, sentience can be defined as an ability to perceive subjective states (i.e., "This situation is good for me", "This situation is bad for me", etc.), and self-awareness can be defined as awareness that one exists, and recognition of oneself, as an individual, distinct from others. Based on these very simple criteria, it shall be shown that the widely-accepted assertion that only humans, and only humans at a certain ontogenetic stage, at that, possess these qualities is simply not concordant with the evidence at hand presently.
Let us start with the evidence from those creatures closest to home, so to speak, with members of the same species in which these qualities are accepted as existing, Homo sapiens, but at an ontogenetic stage where it is assumed not to possess them: neonatal and prenatal humans.
It is very common to encounter statements that a fetus is not conscious, sentient, or self-aware. Some even go as far as saying that a newborn baby, after birth, does not yet have those qualities. Yet a cursory overview of the scientific literature on this subject reveals these assertions to be grounded more in preconceived notions than on fact. A study has shown that newborn babies can recognize the sound of their own cry when heard among the sounds of other babies' cries and the sounds of other animals, revealing a type of self-awareness at the neonatal stage of life. And this is purely anecdotal, and thus cannot count as empirical scientific data, but one of my own cousins once removed, at six months after her birth, has, according to her parents, already developed a preoccupation with her own reflection in mirrors, a preoccupation which she does not display when observing the reflections of other objects in mirrors, an indication of an awareness of a sense of self.
A study by Umberto Castiello et al. has revealed that, at least as early as fourteen weeks in utero, twins have been observed touching each other. The first inclination of the reader would be to dismiss these motions as mere reflexes, but the authors point out that they seem purposeful and directed. This study examined five pairs of twins in utero, and all displayed this same behavior, with the authors therefore arriving at the conclusion that "These findings force us to predate the emergence of social behaviour".
Let us now move on to the likely even more controversial portion of this article, that concerned with the research indicating the existence of these qualities, as well as numerous other cognitive capabilities, such as problem-solving and communication, in creatures completely lacking brains or nervous systems as we know them, such as plants, protozoa, and bacteria.
Any mention of plant sentience, consciousness, or self-awareness is immediately marred by association with the pseudoscience that, sadly, cast a dark shadow over investigations into this subject decades ago, beginning with the publication of The Secret Life of Plants, a book which claimed that doing things to plants such as playing certain varieties of music to them would allow one to communicate telepathically with them and convey emotions, among other such mystical claims. This has led to the investigation of plant cognition being seen as taboo by serious botanists nowadays, a rather unfortunate reality, now that renewed research is beginning to show that this avenue of investigation is, indeed, worth pursuing.
The work of scientists such as Stefano Mancuso, Richard Karban, and Monica Gagliano on plant communication and learning has spread shockwaves throughout the botanical community, bringing up memories of the not-too-pleasant specter of the pseudoscientific claims engendered by The Secret Life of Plants and its ilk. Yet this research cannot be ignored. It has been shown by the work of Karban and Mancuso that plants are capable of communicating to each other through chemical signaling, with some even likening the chemicals released after grass is cut that give it such a characteristic smell as "screaming" intended to warn surrounding plants of the impending danger. Additionally, experimental research carried out by Gagliano has shown that some plants are capable of learning that a given stimulus is harmless after being exposed to it repeatedly, while giving a defensive reaction, showing that they still suspect it might be harmful, once subjected to a different stimulus.
This has led to the development of a nascent branch of botany known as plant neurobiology, which is a misnomer, as even the botanists who study it are aware that plants do not possess neurons, in the same way that animals do. While still an emerging field, it already has made promising progress, and many more insights into plant social behavior and cognition certainly await in the future.
Let us now move on to the organisms that are commonly thought to lie at the very bottom of the Scala Naturae of old, the microbes and protozoa. Even these seemingly most unlikely of candidates for the presence of consciousness, sentience, and self-awareness have no shortage of studies expounding the evidence for the presence of these qualities in them.
Some of the most persuasive evidence in this area has come from research on a certain species of Slime Mold, Physarum polycephalum. This slime mold has been shown to be capable of memorizing its history of spatial location, and of navigating a maze with such precision and ease that it would fill the most clever of human engineers with envy, as it would be comparable to their most carefully calculated efforts.
In addition, bacteria offer an impressive reportoire of cognitive and social behaviors. Bacteria are capable of processing input from their environments and producing outputs in return based upon their computation of said information. They also possess an ability known as quorum sensing. That is the ability to detect when a group of their own species has reached a sufficient number to be able to carry out a certain operation, implying some degree of social awareness. According to a study by the late Eshel Ben Jacob et al., bacteria display some cognizance of the distinction between themselves and others, i.e., self-awareness. Indeed, the actions of bacteria within the bodies of host organisms, and their ongoing battle waged with said host organisms' immune systems, has been compared in its complexity to human guerilla warfare. Bacteria are also capable of genetic engineering, incorporating foreign DNA into their own genomes. In other words, bacteria have had the ability to genetically engineer for billions of years, while humans have now had it for less than a century. This evidence is too impelling to be ignored. Renowned bacterial geneticist James A. Shapiro states that "This remarkable series of observations requires us to revise basic ideas about biological information processing and recognize that even the smallest cells are sentient beings."
I will be posting much more on this topic in the near future, but it shall suffice to say that we must be more open-minded about consciousness, sentience, and self-awareness in numerous varieties of creatures, from microbes to slime molds to plants, and, therefore, by extension, to zygotes, embryos, and fetuses of all animals.