Here is a paper I wrote in October of 2018 examining the question: “Are crystals living things?” This seemingly simple question bifurcates into an inconclusive study of the many definitions of life and an intriguing comparison of crystals to living things based off of these definitions. What do you think; are crystals alive? Comment down below or in the forum, and feel free to be as intuitive and/or scientific as you want!
15 October 2017
Analysis of the Shared Characteristics Between Crystals and Living Things and Study on Definitions of life
Definitions for “life”
Life is defined differently in dictionaries (1) (7), by different scientific fields addressing the subject (2) (3), and by individual scientists studying those fields (9) (10). Entities such as viruses and self replicating proteins fuel a debate concerning whether or not they should be classified as alive or dead. In addition they also provide gray areas, blurring many definitions of life and spawning new ones (2). One conventional and well accepted definition for life requires:
- Cellular composition.
- Capacity for metabolism.
- Capacity for growth and development.
- Capacity to reproduce.
- Capacity to pass on individual characteristics to offspring through DNA: Heredity.
- Tends toward homeostasis.
- Capacity to respond to stimuli.
- The capacity for adaptation through evolution.
A definition similar to this can be found in many textbooks on biology (4). It will be referred to in this paper as the textbook definition. The aforementioned dictionary definitions (1) (7) will not feature in this paper, as their content and more is provided by the textbook definition and, therefore, reviewing them seems irrelevant to the following purpose: This paper explores whether or not crystals can be considered living under the above definition and others, first by scrutinizing crystals under the textbook definition criteria and then under other definitions. This paper then speculates about the definitions of life and why they are important or not.
Do crystals have cells?
A crystal is defined as a grouping of atoms or molecules arranged in an ordered, repeating pattern. The specific patterns are known as crystal lattices and are defined by the geometric structure of their unit cell. A unit cell is the basic structure that is repeated to form a crystal lattice (5). All crystals must maintain a charge balance; an equal amount of positive and negative charge. Crystals whose external boundaries are described by well developed faces are known as euhedral. However, not all crystal possess this feature. Additionally, crystals may not maintain their structures under changing conditions such as increased or decreased temperature, pressure, etc, but rather will assume different forms, called polymorphs, under certain conditions, while maintaining original elemental composition (6). These characteristics of crystals may demonstrate that they can be defined as living.
1. The structural, functional and biological unit of all organisms.
2. An autonomous self-replicating unit that may exist as functional independent unit of life (as in the case of unicelluar organisms), or as sub-unit in a multicelluar organism (such as in plants and animals) that is specialized into carrying out particular functions towards the cause of the organisms as a whole.
3. A membrane bound structure containing biomolecules such as nucleic acids and polysaccharides.
Definition number one is the most general and will be considered first. Different domains of living creatures have cells organized different ways, i.e. prokaryotic, eukaryotic, and archaeic (11), and have different although similar functions and composition. The same is true even at the taxonomic level of kingdom, e.g. plant cells vs. animal cells (12). If science were to accept another general classification of living creatures, e.g. crystals, it might find that that kingdom also differed in its cellular structure.
The definition of a crystal, as provided above, includes that crystals are made up of cells. They are called unit cells and are the basic building blocks of crystals. They make up the crystal lattice, the structural component. They control the functional aspects of crystals by having interstices, vacancies, and other “defects” that shape the physical properties of crystals and control the movement of atoms in and on crystals. They do this by a process where atoms move from areas of higher atomic concentration to lower atomic concentration called solid state diffusion (13). This process also controls the uptake of elements and compounds into solid solution (15). Since crystals are composed of one of the seven types of unit cells (16), their functioning on a “cellular” level is determined by their unit cells. Unit cells are the basic unit of crystalline solids, so, granted crystals are alive, unit cells are biological units. Thus the first definition of a cell can be satisfied.
In the second definition, the word “autonomous” is used. It is, of course, defined in the biological sense of the word. In that sense, it simply means having an independent existence and governing laws (17). Certainly a unit cell satisfies this definition.
The second term in definition number two is “self-sustaining.” Now, as an article by Astrobiology Magazine entitled, “Defining Life”, (18) points out, no organism can survive by itself; all life needs access to free energy and materials. So, it seems that “self sustaining” must mean that the organism can gather the energy needed to survive from some necessary materials, if they are available. Could a human, for example, self-sustain itself in space? Of course not; the proper environment in which a human could survive is not provided in space. One would not stretch logic to say that every organism needs a specialized environment to survive with proper temperature, weather conditions, food supply, etc. For a crystal to form, it needs its constituent elements close at hand. One example of a favorable environment for a crystal is a solution supersaturated with its constituent element(s). In this environment, crystals will form via nucleation (19) and will impose their structural template onto free atoms of their constituent element and organize them into more crystals (20).
The stipulations of the second definition have all been covered save one: the requirement for cells to be “specialized.” The biological definition for this term is to be set apart for a particular function (21). There are several types of defects in crystals that can enhance certain ones of their functions (13). These “defective” unit cells are set apart from the others and perform a different function; arguably, they are specialized.
At the tertiary definition of a biological cell comes a screen that some crystals cannot pass through. That is the requirement for cells to contain biomolecules and to be wrapped in a membrane. A “biomolecule” is simply an organic (containing carbon) molecule produced by a living creature (22). Obviously this criterion is impossible for a crystal not containing carbon, i.e. inorganic, to meet. But many crystals are organic (23). And therefore all of those, except those solely of carbon, contain biomolecules, if it is granted that crystals are alive. Yet if one grants that crystals are alive, obviously the current scientific conclusion that all life as we know it is carbon-based (25), dissolves. Furthermore, the article referenced (25) goes on to accept the possibility that, although the carbon atom seems the most suited for life, life forms could be based around other elements such silicon or germanium. Why, then, should the definition of life be shackled to carbon?
The next hurdle, however, seems too lofty to leap: the unit cells of these crystals are not surrounded by any membranes. This shortcoming is perhaps excusable because nothing is surrounded by a physical, as opposed to an electrical, membrane at the molecular and atomic levels. Organic cells are enormous in comparison to unit cells. For example, a red blood cell is eight micrometers across (39) and a unit cell of Nickel is about 350 picometers across (40): the red blood cell is about a little under 5000 times larger than a unit cell of nickel, length wise, and even more astronomically tiny by volume. Since membranes, in general, are made up of molecules, how could something the size of a molecule, such as a unit cell, have a membrane? Additionally, if one could grant, for the purposes of argument, that crystals are alive, they would be an entirely different sort of living creature from those biologists are accustomed to. There is no reason to assume that such an entirely different form of life would necessarily depend upon membranes.
In sum, it has been determined that crystals are composed of cells, granted a general definition of the term.
Do crystals have metabolism?
Crystals are now going to tested by the second criterion: the capacity for metabolism. As above, the discussion will begin with a definition; the Cambridge Dictionary (24) defines metabolism as “the chemical and physical processes by which a living thing uses food for energy and growth.” The previous section on the cellular composition of crystals explained that crystals do grow. Their “food” is comprised of the elements that constitute them. These elements align themselves into the crystal lattice, so the crystal is using their energy to grow. This growth will be covered in further detail in the following section. Crystals, then have a capacity for metabolism.
Can crystals grow and develop?
Closely related to metabolism is the capacity for growth and development, the third criterion. Anabolism is the specific term for growth (26). Crystals can grow out of supersaturated solution (20), vapor, and solid mineral deposits (27). The process by which crystals grow has been explained above. As crystals grow, they attain a greater size and their individual compliment of defects and impurities. This is the unequivocal growth and development of a crystal.
Can crystals reproduce?
The next criterion and perhaps the most important is the capacity to reproduce. Reproduction simply means “the production of offspring by organized bodies” (28). In addition to being able to form naturally by nucleation (19), crystals can form much more quickly by a process called seeding. Seeding involves placing microscopic crystals into a favorable environment for crystallization to accelerate the growth of crystals (29). This is the way in which a crystal reproduces: a piece of a crystal is chipped off the parent and the chip, or seed, carries the information to form new crystals in its unit cells. When it finds a favorable environment abundant with “food”, new crystals, or offspring, are made. This process is asexual, because the offspring are clones of the parent (28).
The offspring described in the previous paragraph cannot rightly be offspring if they don’t share characteristics of their parent through heredity, the capacity for which is the fifth criterion. The offspring of asexual reproducers are clones of the parent and have essentially identical features. This is, of course, untrue if the offspring grow up in a much different environment than the parent did, and develop differently. The way in which crystals pass their traits to offspring is through a universal code that defines the structure of each crystal. The crystal structure acts as the blue print, like DNA for a new organic organism, a new crystal.
Unfortunately, this process cannot meet the definition of heredity which is complex and restrictive. Heredity is defined as the natural process by which parents pass genes to offspring (30). Genes are chemical patterns on chromosomes that shape the development of offspring (31). Crystals cannot be said to have this characteristic. However, the purpose of genes is to shape the offspring to be like the parent. Although the process described above cannot be called heredity in the strict sense, it clearly accomplishes the same thing. If crystals are a new life form, they have simply found a different way of passing on their characteristics to offspring.
Do crystals maintain homeostasis?
Every living organism needs a specific needs a specific set of conditions to survive; temperature, pH, salinity, etc must all be within a certain range for a given creature to live. Internal conditions are even more important than external ones. Homeostasis is the process that an organism uses to maintain the same internal conditions despite external changes (32). These processes only work within limits, of course: if a human were plunged into the Sun, homeostasis would not help it.
Crystals have something which could be thought of as homeostasis: an equilibrium crystal shape (ECS). ECS is the shape of a crystal at which it has minimum surface free energy, given a constant volume (33). This is the shape at which a crystal is “happiest.” To demonstrate, imagine a crystal at its ECS. If one filed off a corner, after a while the crystal would reorganize itself back into the ECS (34). A NASA article acknowledges that crystals can maintain equilibrium (2). These data affirm that crystals perform homeostasis.
Can crystals respond to stimuli?
Probably the easiest criterion to satisfy, the capacity of life to respond to stimulation, is considered next. Several pieces of information already provided exemplify response to stimulation. The homeostasis of crystals described above constitutes a response to stimulation. Also, liquid crystals can respond to light, heat, and mechanical stress (35). Certain photonic crystals are responsive, as well (36). The aforementioned NASA article (2) also states that crystals can “move” in response to stimuli. Surely this point is affirmed.
Can crystals evolve?
The final criterion: The capacity to evolve through adaptation. This is, arguably, the characteristic furthest from relevance to the discussion, because it is unclear and hitherto unproven whether bodies normally considered alive today do indeed evolve (3). However, according to the article referenced, there is an enormous collection of data that perhaps the majority of scientists think validates the evolutionary process, as described by a website entitled “Understanding Evolution” (14). Seemingly, though, another individual could consider the facts and develop a different interpretation, or theory. Furthermore, Steven Benner in an article entitled, “Defining Life” (8) describes how fictional characters, such as androids, that humans today would be forced to consider alive, would not be subject to Darwinian evolution.
Benner posited that humans would acknowledge the living status of such hypothetical creatures, based on our “values” concerning what is alive. For example, if an unconventional being such as a cloud were to float one day into a person’s path, and verbally refused to move, displaying sentience, could that person consider the cloud dead? The capacity for evolution does not seem to be one of the characteristics of life familiar to us that people value, such as response to stimulation, reproduction, etc. The reason for this may simply be that evolution is not observable. It is inconsequential to transient individuals. In fact, most creatures, including some humans, normally only think about reproduction, growth and development, and response to stimuli. The other, less visible ones, such as heredity and cellular composition, are at least observable within a lifetime.
If this weren’t enough, some definitions for life completely exclude the capacity for evolution as a criterion (37). So even if crystals do fail this test, that will not negatively impact their prospects of meeting the criteria of accepted definitions. But, for the purposes of argument, let us assume universal evolution to be true; Do crystals undergo this process?
To answer this question the Cairns-Smith theory will be considered. It stipulates that the first organic life arose from clay crystals that stored and replicated a genome simple enough to have spontaneously arisen (38). The article referenced explores how hypothetical clay crystals might have evolved due to resource scarcity. An ability of crystals to run programs that predict the most abundant resource available in their environment, which would allow crystals to grow faster, might have developed. The research in the paper concludes that it is conceivable for real crystals to have evolved into responsive, sensitive, creatures. This is no real evidence, but a possible proof of concept.
Although this paper has failed to demonstrate that crystals evolve, and therefore failed to completely satisfy the definition it set out to, other definitions that, perhaps rightly, exclude the evolution criterion, have been satisfied.
Cybernetic definition of life
The textbook definition scrutinized above is not the only proposed definition of life. A cybernetic definition defines life as a network of regulatory mechanisms subordinated to a potential for expansion (9). Crystals certainly possess a network of regulatory mechanisms, and harness these to expand. Unless that extrapolation harbors a misinterpretation of the cybernetic definition, crystals do satisfy it and contain “the essence of life” which, as the authors of the referenced article suggest, the cybernetic definition embodies.
Value based definitions of life
A previously referenced article mentioned that one way of determining whether or not something is alive based on our values (14). People in general seem to value life for its responsiveness, its growth and development, and its reproduction. The one of those features that isn’t obvious in crystals is responsiveness, although they do possess this characteristic, as argued above. More importantly, though, they don’t respond in ways that humans can naturally interpret. This lack of intuitive understanding is probably a reason why people generally do not consider crystals alive.
At first glance, a coral reef may look inanimate, but with a scientific background one knows that they are alive. Science has provided this viewpoint. It is hard for the unaided human to observe the living properties, such as growth, of a coral reef. Crystals naturally grow very slowly as well. This slow growth of crystals is perhaps another reason that crystals aren’t considered living.
In contrast, a tree seems to grow just quickly enough for people to observe considerable growth in a lifetime. In addition, trees are far more abundant and ubiquitous. Crystals, however, are less obvious and generally paid less attention. Seemingly, for a long time humans in general failed to observe these important characteristics of crystals as a consequence of there inattentiveness and short life spans. Yet, when science began to study crystals, it was too late: people had already developed a system of somewhat arbitrary values that determined in their minds what was alive and what was not.
In consequence, humans have thought nothing of harvesting and exploiting crystals for their beauty and their great utility in electronics, building, etc. However, this would not be surprising even if humans did consider crystals to be alive. Consider what they have done to creatures in the modern farming and livestock industries. Obviously nothing can be done for the unfortunate case of crystals while those atrocities on more obviously living things (including humans) continue. Of course all living creatures depend on each other for survival, but humans have learned to satisfy their greed for wealth and convenience at an unprecedented level, to the detriment of all life, crystals (perhaps) included.
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