Evolution by natural selection is the central principle of all of biology and no field of biology has been affected more so by evolution as described by Darwin then confirmed through the Modern Synthesis. Indeed, I consider evolution to be the “Grand Unified Theory” of biology since every finding in biology from biochemistry to ecology has to consider evolution in solving “ultimate” questions or “why” questions. No other satisfactory explanation but Darwinian evolution has proven so successful in solving ultimate questions hence its importance in all of biology.
In a way, Darwin unified biology much as Newton unified physics through his laws of motion and universal gravitation where previously it was thought that the natural laws of the cosmos and the earth were once separate things were shown later to be described by the same laws and Newton emphasized careful mathematical reasoning and scientific experiment in setting up theories that can be tested and confirmed, at least in physics.
Darwin, like Newton, emphasized observation and experiment when establishing the foundation for the theory of natural selection and for each step leading up to natural selection, evolution of populations of organism is inevitable and the unification of all of biology was possible by first adopting population thinking and through population thinking was Darwin able to proceed to his theory of natural selection which has been confirmed through experiments and after biologists also adopted population thinking, could the Modern Synthesis proceed in making evolutionary biology a legitimate science and thus the unification of biology through ultimate questions.
But there is more than just a simple comparison of Newton and Darwin and I would argue that Darwin was not operating independently of the Newtonian worldview and although Darwin was a biologist and Newton a physicist but Darwin was in a way operating within the framework of the Newtonian worldview and this worldview emphasized cause and effect which is part of physics, for every effect there is a cause and that it is the purpose of science to isolate whatever cause results in a specific effect.
Darwin clearly knew that for evolution to occur or “descent with modification” (1859) as he would have called it originally, there had to be a discernible mechanism which if you have read my other blogs about Darwin and evolution, you would have correctly guess it as natural selection and you would be correct. Previously Newton realized that the force that holds planets in their orbit around the sun was caused by that force , gravity so the motion of planets as well as falling objects were caused by the force gravity and the effect of the force is to change the direction and speed of orbits.
Something like the equivalent of the universal law of gravitation for the living world was found by Darwin in that all the diversity of life is the result of evolution from past ancestral populations and that the evolution (the effect) is the result of the mechanism of natural selection acting at the level of the individual in any population (the cause) just like the fact that the orbit of planets (the effect) is the result of gravity (the cause).
The foundation of classical mechanics, the field of physics that studies the motion and forces of particles depend on Newton’s three laws of motions from which all of physics is based on and has had success in predicting the trajectories of planets to launching satellites into orbit. Is there something similar for evolution? Indeed there is something like the three laws of motion for evolutionary theory and in my first blog “Population are the Key to Evolution” I talk about how populations and variability results in natural selection. But if Darwin was to form a theory that would unify all of the fields of biology which not only attempt to answer the “how” questions or proximate questions but the “why” questions or “ultimate” questions.
The theory of evolution is supported by natural selection and natural selection is based upon three observations that Darwin made during and after his trip aboard the Beagle just like the law of universal gravitation is supported by the three laws of motions, we can compare and contrasts the findings of Newton with that of Darwin and to see that evolution in the biosphere is inevitable I will compared Darwin’s three observations with Newton’s three laws of motion and by making the comparison, we can see how natural selection allows for evolution but also by seeing why evolutionary theory after Darwin had such an profound influence in the science of biology which thereafter modern biology cannot do without.
Newton’s First Law: Every object is in a state of rest or in a state of continuous uniform velocity and will continue to be in that state of motion unless acted upon by an external force
In essence, this fundamental law of motion is nothing but the law of inertia or the tendency to resist change. Every object with mass is either stationary or moving in a straight line motion in any given direction until an external force causes it to change it’s velocity or speed in a given direction in an amount of elapsed time. This law of motion I think is what is one of the crowning achievements of the Newtonian worldview which was first given an experimental basis by Galileo but was presented by Newton in a form that can be predicted not only theoretically but confirmed by experiment. Indeed all the laws of motion can make predictions which can be confirmed by experiment as it has been done and this became part of physics prior to the advent of quantum mechanics which will not be discussed but suffice it to say, Newtonian mechanics or classical mechanics after Newton has had a profound influence in western thought.
But you may ask: What does this have to do with biology especially evolutionary theory? To understand how the Newtonian worldview was an influence on Darwin and how Darwin’s initial observations lead to evolutionary theory as elaborated in detail in my blog “Populations are the key to Evolution” as well as in my other blog “Typology versus Population” ( I strongly recommend that you read these two blogs first in order to follow the argument in this blog) Darwin began to adopt a new form of thinking that set him apart from previous thinkers in regards to evolution as Darwin was not the only scientist to think about such matters but what set him apart was that he adopted a new form of thinking that Mayr (2001) called “population thinking” and it was this adoption of this radical form of thinking, radical in the sense of the predominant thinking in the western world, that Darwin could legitimately be called the “Newton of biology”.
Just how did Darwin accepted population thinking and how does his acceptance allowed his later theory of evolution to justify his title as the “Newton of biology” if his thinking was operating within the Newtonian worldview? Shortly after his voyage from South America and upon his return to England, Darwin was convinced that life evolved from previous ancestors and through time, became different gradually from their ancestors. Before the South American voyage, Darwin like his fellow thinkers believed more or less that life was the same during the beginning of creation and he was also educated with what is called “natural theology” or by studying life and all of it details, one can be lead to conclude that this was the work of God and was of course advocated by British theologian named William Paley and briefly explained by Dawkins (1986) as “Argument by Design”.
Darwin was brought up by the tradition of natural theology along with the belief in deism or the belief that God created the universe but simply steps aside and does nothing afterwards. After the voyage, Darwin was convinced that life is not static but dynamic or can change through immense periods of geological time. But even with a proposed explanation for life evolving from a simple ancestor his proposal would be no more better than other alternative proposals of evolution unless he provided evidence for a mechanism that could be observed that can account for the diversificiation of life both past and present.
Recall that in physics it is the task of that science to isolate the cause for each effect and in biology, if the effect of the long ancient history of earth is that on its surface in oceans there are a diversity of life forms, then what is the cause of all that diversity? To find the cause, Darwin needed an equivalent of the first law of motion but applicable to biology and in Oct, 1838 he found his answer by reading a work by Thomas Malthus on population growth.
It was by studying population growth that marked a crucial transition in locating the mechanism for evolution or natural selection as Darwin was the first to coin the term for his proposed mechanism. What was it about Malthus’s work that had such a profound influence on Darwin’s thinking and how was it equivalent to Newton’s first law of motion?
According to Malthus, who focused on human populations growth, human populations grow much faster than the resources needed to support a population of humans and by focusing on human population growth Malthus argued that the growth will strip all the vital resources such as food and space, and conflict is inevitable.
Darwin used Malthus’s argument of population growth and applied that same logic to every population of living organisms. Organisms in populations do show rapid growth and ideally will expand their population sizes if there were infinite space and food. Exponential or rapid growth of populations is equivalent to the law of inertia for in that physical law, an object in uniform motion will continue to move in a straight line as long as there is no external force stopping its motion. Likewise population growth is like inertia in that if there is infinite space with infinite food, a population of organisms can continue to expand in size indefinitely.
Sooner or later, an object in uniform motion will encounter a force causing it to change direction and/or speed or stop completely. The same is true for real populations: they never keep growing since for every population in whatever natural environment, a population will grow unless there are predators that feed on some of the individuals, food supplies dwindle resulting in starvation. Indeed predators and limited food supplies act to slow down population growth and these limiting factors are like the external forces changing the inertia of a moving objects.
For natural populations, most individuals will not survive through these kinds of limiting factors but some will survive. What is about those survivors? Once Darwin accepted Malthus’s main argument and applied it to his work, thus making the transition to population thinking, it was found that in a population, no two individuals are alike. There are small differences in the ability to run, to hide from predators, the shape of a carapace, and so on from each generation and these variations in traits or phenotypes makes a difference between survival and perishing and those individuals with surviving conferring traits are likely to live through whatever changing conditions are in their environment and so gradually the population evolves into a new population into new forms. This is equivalent to an object with inertia changing its position from a linear to a non linear trajectory such as a planet in a star’s gravitational field.
With the appearances of novel traits with surviving conferring benefits, a population can slowly adapt to new changes in its environment. These limiting factors such as scarce resources and individuals differing from their parents can result in differential survival of each generation and also at the level of the organism, it can either survive or perish and gradually in each generation, a population can either remain the same as its ancestral population or evolve into a different population and with Malthus’s main argument, Darwin used that as the foundation for proceeding to the mechanism that he is famous for finding and that is natural selection.
Natural selection can be thought of as a “force” that cause populations with heritable variations to evolve into new speceies. With naturals selection, we can then proceed to Newton’s second law and see how that translates into naturals selection as the “force” that alters the trajectories of evolving populations.
Newton’s Second Law: Force is equal to the product of the mass or inertia to the acceleration
A force is anything that can change the speed of a moving object or its direction and that depends on the object’s mass or inertia along with its change of velocity or acceleration. What is the equivalent of the second law for Darwinian evolution?
Recall that Darwin made the breakthrough in accepting Malthus’s insight on population growth which was originally studied for human population but the same is applicable for any living population past or present. If there were nothing to prevent to slowing down of population, any population of organisms, no matter how big or small, will grow exponentially and that is the same as an material object’s inertia but in reality there are plenty of factors that stop populations from growing exponentially. These factors are like the external forces that alters a moving object . In fact, on the level of the organism which is where Darwin placed emphasis, within the context of the population, it could either survive or perish if it had heritable traits which allow it survive in a novel environment or not.
Gradually through the vast stretch of geological time, a population can either evolve into distinct separate populations, each adapted to various kinds of environments, be adapted to one specific environment, or go extinct.
This is made possible because of the environment which acts as the external force and that external force is natural selection. Starting at the level of the organism, natural selection acts at every stage in the life cycle of a reproducing organism from embryo to the adult, and at each stage of the life cycle, the developing organism must have heritable traits that favor survival but in order to have these traits, they must arise from the process of reproduction and the cause of the variations are the result of changes in the genes together with recombinations of sets of genes on chromosomes in the process of meiosis, but I’m getting ahead for although Darwin knew that without heritable variations, there can be nothing for natural selection to act on, Darwin was unable to locate the source, since I’ve stated previously that every effect such as variation can be traced to a cause which are genes, and that was made possible by the field of biology, genetics.
Also , as carefully explained in my blog “Typology Versus Populations”, a population of organisms consists of individuals with varying traits so no two are alike. That is a consequence of reproduction, and even though offspring do resemble their parents, the resemblance is not perfect so variations are inevitable. The variations if slight will make a difference in survival and in each generation, a population will slowly change to a different and even distinct population that is adapted to a changing environment which is made possible by natural selection.
Like forces that shape the form of solar systems and galaxies or even of atoms and molecules, natural selection has resulted in the vast diversity of life. With a precise and quantifiable definition of force, Newton was able to proceed to the third law and Darwin did something similar. At first as pointed out by Mayr (1988), natural selection was originally an inference when Darwin was attempting to explain what would happen if a population had heritable variations in each generation. It was no more than a hypothesis but a testable hypothesis
Newton’s Third Law: For every action there is an equal and opposite reaction
Particles exert forces on other particles in the forms of pushes and pulls resulting in changes in trajectory. Natural selection acts on each population in a similar way, pushing for the survival and even the extinction of evolving populations. For example, suppose there are a population of rabbits but these rabbits were slow moving rabbits. As long as there are no predators, the populations of slow moving rabbits will continue to thrive in their habitat but now there are a population of foxes which have the ability to smell and run towards their prey which are the slow moving rabbits. As you would expect many of the rabbits succumb to the predation of the foxes but assume that this is a large population of rabbits and in each generation there happens to a few offspring of rabbits that have differently shaped hindlegs, so shaped that these few individuals run faster compared to their normally slow siblings.
These few rabbits with the ability to outrun the foxes now have an advantage in that they can escape their predators easily and with that new ability, where previously there was no such survival conferring trait in the previous generation of rabbits, these rabbits can reproduce with the surviving rabbits, and on average there will be more and more offspring that can outmaneuver the foxes so gradually the population evolves into rabbits that run fast instead of slow and this was made possible by the population of foxes, which exerted the selection pressure for the rabbits to evolve into speedy organisms.
Likewise, the population of rabbits also exerts a selection pressure on the foxes. Like the evolving population of rabbits, there is an evolving population of foxes. In order to catch a rabbit, there has to be a few individual foxes with more keener eyes, a more streamlined body along with legs with strong muscles, allowing for faster locomotions. These individual foxes with those kind of traits will also have an advantage compared to the other foxes without such natural modifications.
It is not just rabbits and foxes but every kind of population which exerts evolutionary changes in other populations and that is not to dissimilar to Newton’s third law of action and reaction. In fact this is what is known as the evolutionary arms race which exist between predator and prey and this results in survival tactics for prey populations to avoid or even attack their predators and likewise predators in order to survive , must have traits for locating and moving towards their prey. Predation and survival go hand and hand which allowed diversification of species of the animal kingdom.
Aside from predation, two or more species can coopt with one another where both members have traits that allow for the long term survival of two different species for mutual benefit. A classic example is insects and flowering plants. An insect such as a bee or butterfly can easily sense and collect nectar from flowers but also pollen which are produced by reproductive organs of flowers and while flowers lack the ability to move under their own power for reproduction, they must rely on moving animals to carry pollen from another flower.
This is done if flowers have specialized structure to produce pollens, which are the stamens, and pistils which receive pollen. In order to have pollen transferred from stamen to pistil, flowers must produce scent as well as nectar to lure insects and bees for example have the sensory apparatus to smell and see the flowers which they can position themselves inside the flower where in addition to collecting nectar they end up collecting pollen and so move on to another flower. Bees benefit by taking nectar, a useful energy source as well for making honey. The flowers benefit by receiving pollen while minimizing the risk of self fertilization since all flowering plants are hermaphroditic.
This is a fine example of coevolution and in the case of species being affected whether by benefiting both species, which is known as mutualism or through predator and prey relationships where both prey and predator evolve traits that allow for survival, this is the biological equivalent of Newton’s third law.
Physics was placed on a quantitative basis with Newton’s laws of motion which became classical mechanics and deeply influenced the scientific course of physics. Darwin did the same for biology which aside from causing conflict with those deeply held personal beliefs indicative of the western world, gave biology a foundation that at first with its emphasis on naturals selection was at first hard to accept but after the Modern Synthesis became the accepted consensus and ever since then the syllogisms that lead to natural selection have been confirmed and there has yet to be any evidence, if any, that contradict the predictions of natural selections. Darwin isolated the cause for evolution which is the observable effect in both the living world and in the fossil record. Together with his acceptance of population thinking, it is justifiable that Darwin can be considered the Newton of biology.
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