Chance, Necessity, and Evolution


All of life that is present in the biosphere is the result of a slow gradual accumulation of genetically inherited differences from previous generations of life, many of which are extinct but for every extinction and because of natural selection, each survivor, large or small, had qualities allowing them to survive in each change in environment.


Life is a true success story having survived each catastrophe and through natural selection, will continue to do so. Since life , in order to survive, relies on resources from energy flow to genetic mutations and recombinations, and since all of the information needed to form a living organisms comes from its genome, how does the combination of chance, in the form of mutations and natural selection, a non random process of elimination, work together to produce the diversity of life?


Rather, to what extent natural selection or necessity plays a role in shaping the course of each lineage of each species and also to what extent chance processes such as mutation and genetic drift, an random evolutionary process, also influence the outcome?


This reduces to a question of inquiry which can be traced back to Ancient Greece where philosophers debated to whether or not the world is the result of chance or necessity that is everything in the world a material combination under blind chance or is the world the outcome of a plan, which could either be accessible to human reason. The answer as revealed by Darwin and as far as the biological world goes is that both chance and necessity play a part.





The ancient Greek philosopher, Democritus of Abdera was one of a long line of philosophers who asked questions and tried to form answers based on sound logic and reason without the need for divine intervention and previous philosophers before Democritus believed that everything living and nonliving and indeed the world was made out of a single substance and although Democritus believe that like the philosophers before him, everything is a manifestation of a fundamental substance, it was Democritus who proposed that everything is composed of atoms, a term that he himself used, although he borrowed this concept from his mentor, Leucippus and sometimes it is hard to tell who it was used that originated the concept since much of Democritus’s work has been commented on by later writers, nonetheless Democritus gets the credit for pursuing the inquiry about the fundamental nature of the world , an approach that is more philosophical than empirical.


According to Democritus, all of matter is made up of atoms, particles that are very small, have a variety of shapes and are innumerable. The atoms are constantly moving in all directions and various speeds and some are colliding with one another, while others are moving apart.


In order for motion to occur, there had to be something through which the atoms could move through and that, according to Democritus, was empty space or void. Void is empty and as long as it is empty, atoms can move so in Democritus’s world view everything is composed of atoms and void and every material thing whether living or not, is the combination of atoms.


Although not stated explicitly in Democritus’s writings, what this world view implies is that every combination of atoms is a chance process. There are a total number of atoms , each atom is indivisible and will never completely disappear but with each unique combination will form whatever material object there is for our senses to perceive but every unique object that exists or will exists is a random combination of the atoms , that will form objects sooner or later, and disappear sooner or later. Everything is the result of chance as part of Democritus’s world view.


Of course, not every philosopher agreed that everything is the result of chance processes. Some philosopher believed that there was an order or necessity and that everything was the result of a process that was orderly as well as accessible to human reasoning and there would be no room, if any, for chance to play a role. One of the philosophers who had such a profound impact on western thinking was none other than Aristotle and in a way Aristotle would have been the opposite of Democritus. Instead of everything appearing as the result of chance, everything that appears is the result of purpose or necessity.




Of all the philosophers of Ancient Greece, none had a larger impact on the outcome of western thinking than Aristotle. It was the philosophical investigations of Aristotle that had a deep influence in rational inquiry or the inquiry of a world through logic, as defined by Aristotle, in order to understand the world. Of all contributions that he made, was the formulation of the concept of “causes” or what makes something respond to something else in relation to one another and that one can separate cause from effect. The causes can be small to large and so are the corresponding effects. What this implies is that Aristotle realized that there is order in the world , which would be called “necessity” and this can be seen from what is called “material causes” or things that are as a result of being made of something physical such as a statue carved out of stone. The statue can be a human form in a pose or it can be in the shape of an animal. The cause of the shape and form of a human was carved out of stone and without the stone there can be no sculpture this being the example of a material cause.


There are other three causes, the “formal cause” is something that can exist in the mind of someone (or something) that has a plan and with a thinking being, such as ourselves, can put that plan into action. The form of a human carved from stone requires a trained sculpture, who in his mind would think about what the human form should be and would end executing the plan by carrying out the action.


The “efficient cause” is something that can make a change in relation to something and it applies to both animate and inaminate objects, and that is cause and effect, for every cause and effect will result.

An example is a patch of ground that is bare but if seeds are sown whether through the action of animals or through humans, the seeds in the ground with sufficient light and moisture will grow into tall plants and eventually will become a forest. In this example, the cause is the presence of seeds, either delivered by animals or by humans, in the ground and the effect is a lush forest that results.


The last cause is what is called “final cause” or “ultimate cause” and this state that everything is the result of a purpose which Aristotle called telos and that everything that exist or will exist is the result of fulfilling the ultimate destiny and that is achieving telos or the goal.


For the last cause is worth considering since this is what defines necessity, so when you accept that necessity, according to Aristotle is order and that everything that forms in this world is the result of order or necessity. It is also worth considering that before he became a philosopher, Aristotle started out as a naturalist and he observed and catalogued the organisms present in his part of the world. He even observed the life cycles of animals such as birds forming as an embryo until they reached mature organisms. The fact that organisms such as birds form from a shapeless organic mass in eggs to a fully functional organisms with wings allowing them to fly , to find food and shelter, and mates seemed to Aristotle that all of life had a plan, a final goal which is order and in this particular example that order is to manifest in the shape of the form and function of a bird. From this perspective, it would be absurd that a random combination of atoms would form such an organism of such perfection so it was with telos that Aristotle as the opposite of chance according to Democritus.


The rational inquiry formulated by Aristotle had a huge impact on science which in Aristotle’s day consisted of observation from the human senses and logical speculation but during the Renaissance and up until the Enlightenment, the scientific method broadened to include experimentation together with the development of new tools such as the microscope which helped broaden our senses to include a world of small organisms too small for the naked eye to see along with discoveries of new plants and animals made possible by explorations of other continents such as Africa and the Americas. In addition certain beliefs such as a belief that the world was constant and static which originated in the beliefs of the Ancient Greek philosophers such as Plato and later into Medieval Christian thought, were starting to become challenged as more and more naturalists as well as geologists were studying the world with a more objective eye and realizing that it was likely that all of life, however different in form and function seem to have some things in common such as the same cell with nuclei (as explained in detail in my previous blog post) and that the internal structure of live organisms are similar or homologous to one another and that most of the animals alive were the descendants of past animals, which were the beginnings of evolutionary ideas or the concept that all of life is the result of past process of changes to previous environments that are different than are today.


To fully form a true evolutionary theory that is testable and observable, we have to go back to what I talked about and that is the natural world of living things the result of chance or necessity? That is the evolution of life a chance process or the outcome of a process that is non random or the result of necessity? The answer is really both and with Darwin and his genius in adopting population thinking ( see my blog “Populations are the Key to Evolution”) where no two individuals are alike and that the difference can mean life or death and that competition between individuals in a population as was first realized by Darwin, it was Darwin that in addition to proposing that natural selection acts to change populations into new species adapted to novel environments but really with his acceptance of population thinking, he solved a conundrum facing scholars whether everything is the result of chance or necessity and the answer by Darwin is that it is both.




Statue of Charles Darwin at the Natural History Musuem in London (Matt Buck)

Statue of Charles Darwin at the Natural History Musuem in London. Darwin introduced the most radical form of thinking, population thinking , which not only gave a sound and scientific basis for modern evolutionary theory but it helped combined both chance and necessity. (Matt Buck)


No other scientific theory in biology had a more unifying and more radical view of nature than the theory of evolution by natural selection, a mechanism that was given the name by Charles Darwin and proposed the first testable mechanism which has been confirmed and strengthened through the Modern Synthesis or the combination of natural selection with genetics. What was about it this theory proposed by Darwin that had such an effect in western thinking that is so profound in its scope and yet continues to be misunderstood? What does this theory have to do with the two seemingly opposite viewpoints of whether the world is a result of necessity or chance? For one thing, when the book On the Origin of Species was published, what is said is that all of life is the result of slow gradual accumulation of small but heritable changes in each individual and if these tiny changes confer a survival benefit to the organism then it will survive until the next generation and through what Darwin (1859) called “descent with modification” or evolution is the result of nature choosing which individual in a population lives or dies and through also through heredity, all of life is not just a descendant of previous organisms that have survived changing environments but that all of life is the descendant of a single common ancestor, and through new techniques in biology, such as molecular biology, has confirmed that all of life does share a common ancestor.


To understand Darwinian evolution is to adopt a new way of thinking that is completely different than the philosophy of previous generations, and even after the publication of The Origin of Species, there was still considerable skepticism towards Darwin’s original view of evolution. Why was that? Aside from the fact that it resulted in conflict with deeply held religious beliefs (usually as a result of literal interpretations of Scripture) another reason for conflict resulted from a misunderstanding of the process of natural selection together with the source for heritable biological variation and the reason for misunderstanding is that even though prior to Darwin, there were evolutionary theories but were based on a philosophical belief called typology or essence or that there are perfect, changeless forms and that everything in the world is the result of these essences. Also other evolutionary theories stressed that all living things are evolving towards a final goal so each living thing becomes more and more perfect, as a result of reaching the final goal.


Of all the non Darwinian alternatives that were offered, only one became the only true explanation and that is Darwin’s evolution by natural selection and the reason why is that unlike all theories based on typology, Darwin theory’s triumphed because it was based on population thinking and not knowing the full meaning of population is one reason why most people , not just the lay public but some scientists who though in typology had a hard to time accepting population thinking and once it was implicitly stated in The Origin of Species and was eventually adopted, Darwin in a way resolved the debate between chance and necessity and through population thinking, both chance and necessity play a part in biological evolution.


For natural selection to work on populations, there must be a continuous supply of biological variations and it is these variations that allow survival and natural selection can choose which individuals in a population will survive or perish, for without variation, natural selection can choose nothing at all. Natural selection is what Mayr (1988) called a “two step process” (p.97). The first step is the process of production of new variation which was already noted by Darwin in that two individuals are not alike. Whatever variations there is will be passed on to the next generation. How are all the variations generated? Although Darwin himself tried to search for the causes, the search eluded him and only when the science of genetics was formalized could the cause of variation be noticed. Variation in organisms are the result of the expression of genes on chromosomes and genes from both parents are passed on to the next generations.


Biological variations are generated by random process on the level of genes as well as chromosomes. Mutations are the sources of heritable variations and result from changes in the base sequences whether an additional base is inserted or removed. These changes on the molecular level and on the chromosomal level are random and are caused by energy in the form of radiation to heat. Any changes that result will either be beneficial, harmful, or neutral. Beneficial mutations are likely to confer a beneficial change such as a novel adaptation to whatever new is present in the organism’s environment such as an ability to digest certain foods which the previous generation could not do so. Harmful mutations will end up killing the organisms and neutral mutations are neither harmful nor beneficial.


The other source of biological variations is meiosis , a form of cell division where a set of cells in a multicellular organisms , the germ cells, have their total set of genes reduced to half, which become the gametes or the sperm and egg and there are two steps in meiosis. The first step involves recombination of the paternal and maternal chromosomes and the second step is the reduction in the number of genes in each chromosomes whether in male organisms it is the sperm and in female organisms the egg which not only halve the number of genes but after the second and last step in meiosis, the genes from the two sets of chromosomes are also randomly distributed.


In the first step, notice that chance is at work and recall that it was believed by Democritus and his followers that because of the random association of atoms, everything in the world is the random association of chance but in the biosphere, whatever genetic variation is produced, mutations, meiosis, or a combination of both, chance processes are involved but that is just half of the process of evolution. Evolution does rely on chance components as far as biological variations are concerned but to say that evolution is solely a chance outcome is really apt to completely misunderstand the entire bulk of evolution and in truth chance is only half of the process. The other half, the second step, is the non random elimination of those organisms that because of “bad genes” as a result of mutations which will not confer any survival value or if the organism had a novel mutation that allowed to tolerate it a change in its habitat such as the ability to withstand cold temperatures where previously it was warm then through non random elimination or natural selection, the surviving generation , because of the production of heritable variations, will produce offspring that will inherit the surviving conferring trait. Natural selection, is really necessity , contrary to what most people assume, ignorant of population thinking , are likely to mistake natural selection as a random process. In fact, it would be better to think of natural selection as what philosopher Dennet (1995) called “an algorithmic process” (p.48).


What is an algorithm? An algorithm is a non random step by step process where in a finite number of steps something is generated since in each steps certain rules are adhered to and an example is long division. Knowing the rules of long divisions divide any pair of numbers and you get a given result, which if you know the rules you can do on paper or for that matter the rules for long division can be done on digital calculators.


What does an algorithmic process have to do with natural selection? You can think of natural selection as something of a filter that lets in organisms in a population in whatever environment and you can think of the environment, with all of its living and nonliving components as that doing the process of selecting. In every generation, variations are inevitable since reproduction is an imperfect process of copying genetic information. Those individuals with traits allowing them to survive will have a better advantage than those individuals that do not.


Dennet (1995) pointed out that algorithmic processs are usually characterized by “if-then” statements; if X then Y for example. There is on paragraph from Darwin (1859) that nicely summarizes the essence and simplicity of natural selection ” If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organization, and I think this cannot be disputed; if there be, owing to the high geometrical increase ratio of increase of each species, a sever struggle for life at some age, season, or year, and this certainly cannot be disputed, then considering the infinite complexity of the relations of all organic being to each other and to their conditions of existence, causing an infinite diversity of structure, constitution, and habits, to be advantageous to them. I think it would be a most extraordinary fact if no variation ever had occurred useful to each beings own welfare, in the same manner as so many variations have occurred useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterized will have the best chance of being preserved in the struggle of life; and from the strong principle of inheritance they will tend to produce offspring similarly characterized. This principle of preservation, I have called, for the sake of brevity, Natural Selection; and it leads to the improvement of each creature in relation to its organic and inorganic conditions of life.” (p.98).


There are “if-then” statements , which forms the logical basis of the algorithm and since algorithms are characterized by a series of steps following one to another until something results from these steps, the steps to natural selection can result when we condense the necessary steps of natural selections which are


1. All life on earth has the ability to reproduce faster or the tendency to produce more offspring and only a few individuals will survive.


2.The surviving offspring will have some traits or phenotypes that allow them to survive while those individuals lacking such phenotypes will be at a disadvantage.


3.The offspring with phenotypes that confer them an advantage will pass on these phenotypes to their offspring.


All of life, and there is no reason to suppose that none of them has passed through each step beginning with the first, and what will happen is that there will be non random elimination of those individuals in a population that were unable to cope with any novel changes and so those individuals will die while the surviving ones will prosper , with their ability to cope with their changing environment.


Thus, you can see since all of life will pass through the first step, natural selection will be the outcome and since natural selection is structured like an algorithmic process, natural selection is anything but a random process. The only random components there are consists of mutations and sudden changes in the population’s environment such as sudden cold in a warm habitat. Natural selection is truly a form of necessity.


I have said that there is non random elimination which is what natural selection really is, and ever since The Origin of Species both layfolk and scientists who studied Darwin’s work were confused as to the meaning of natural selection. In fact, in the first chapter Darwin discusses how humans have selected desirable qualities in plants and animals resulting in all the varieties of sheep, cattle, and produce, and that is what is called “artificial selection” and this is done by humans with a goal or plan in mind. Darwin, an original and insightful genius in biology, was the first to give natural selection its name and definition as you can see from the paragraph above. What this implies is that someone or something is selecting each individual in nature. In a way, as was pointed out by Mayr (2001) natural selection is something of a misnomer since there is nobody that is doing the selecting other than the environment. There is only non random elimination as that processs should really be called but when you understand that natural selection is just non random elimination, then confusion about will eventually go away.


Another source of confusion about natural selection is that unlike artificial selection where a farmer may select out of a breed of animals which individual has a desired trait such as thick wool and then produce a generation of animals with thicker wool and that is because of a goal that the farmer had in mind with a future outcome and that outcome is produce animals with thick coats. Recall that in my discussion about Aristotle that everything is the result of trying to achieve an ultimate goal, the telos, but in natural selection the only goal is to survive in the present. There is no ultimate goal towards perfection. An organisms however simple has to survive and it doesn’t have to be complex and since organism inherits whatever traits it has from its parents, then it whatever environment it is in , that organism will likely survive. Scientifically there is no evidence whatsoever that all of life is evolving towards an ultimate goal and up until the Modern Synthesis, alternatives to evolution were based on something other than population thinking suggested that the evolution of life was heading towards some ultimate endstate but with the acceptance of population thinking which is part and parcel of the Modern Synthesis, alternate evolutionary explanations or orthogenesis as it is called were rejected since these beliefs were outside of formal scientific inquiry and would be in the realm of metaphysics and theology anyway. Indeed as Mayr (2001) said regarding progress, which is called “teleological” or striving towards an ultimate goal in the sense of Aristotle, in evolution ” Selection is not teleological (goal directed). Indeed how could an elimination process be teleological? Selection does not have a long term goal. It is a process repeated anew in every generation. The frequency of extinction of evolutionary lineages, as well as their frequent changes in direction, is inconsistent with the mistaken claim that selection is a teleological process.” (p. 121).


Of course the one aspect of Aristotle that an organism is the result of some plan is in a way correct since each living thing has a genetic instruction or the genotype specifying how the organism is structured, how it functions and how it will reproduce and natural selection depends on the variation that results from any small changes in the genotype.


Chance and necessity are both part of that radical form of thinking that defines the core of Darwinian thought which is population thinking and as also summarized by Mayr (2001) ” by making biopopulations the foundation of his evolutionary theorizing rather than Platonic types,(Darwin) had found an entirely novel solution for the explanation of evolution. He postulated that the inexhaustible genetic variation of a population, together with selection (elimination), is the key to evolutionary change.” (p.114). It is population thinking that is the key to understanding evolution and also through this same form of thinking, both Democritus and Aristotle in a way are both vindicated, and Darwin also succeeded in resolving the tension between chance and necessity when the living world is really the result of both.




Aristotle (n.d) Retrieved on August 25 2015


Darwin, C (1859) On the Origin of Species By Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. London, England: Murray London


Democritus (n.d) Retrieved on August 25 2015


Dennet, D.C (1995) Darwin’s Dangerous Idea: Evolution and the Meanings of Life New York, NY: Simon & Schuster


Mayr, E (1988) Towards a New Philosophy of Biology: Observations of an Evolutionist Cambridge MA: Harvard University Press


Mayr, E (1997) This is Biology: The Science of the Living World Cambridge, MA: Harvard University Press


Mayr,E. (2001) What Evolution Is New York, NY Basic Books


Pullman, B(1996) The Atom in the History of Human Thought (A. Reisinger Trans.) Oxford, England: Oxford University Press




IMGP8061 Matt Buck   CC BY-SA 2.0


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