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b. Basic Theory of Evolution

The Basic Theory of Evolution

Mankind is a consequence of evolution through a combination of random mutation and natural selection. Charles Darwin first postulated this process in 1858 and published it in his 1859 book “On the Origin of Species”. At the time, DNA and its role had not been discovered and Darwin referred to a more general principle of inheritance. DNA was first discovered in the 1860s by the Swiss chemist Johann Friedrich Miescher but its central role in the evolutionary process was not understood for almost a century thereafter. In the early 1950s Rosalind Franklin produced an Xray photograph of DNA which, in 1953, enabled James Watson and Francis Crick to discover its double helix structure. This in turn enabled them to explain how it carries and replicates genetic information. Since that time, a substantial amount of scientific evidence has accumulated in support of Darwin’s theory.

An organism’s genes are sequences in its DNA which either directly or indirectly enable the manufacture of molecules whose function determines the organism’s characteristics. These characteristics, in turn, determine the organism’s ability to survive and reproduce within its environment.

Random mutations are changes in the DNA sequence and, thus, in the organism’s genes.  They are an example of the impact of entropy on life. They can be caused by errors in DNA replication, by exposure to damaging chemicals, by exposure to radiation or by the insertion or deletion of segments by mobile genetic elements such as viruses. Mutations are entirely random and are not in any way pre-determined to benefit the organism. Most mutations (about 70%) are, in fact, harmful and the remainder either neutral or weakly beneficial.

Natural selection means that organisms with hereditary characteristics most suited to their environment, i.e., the fittest, are most likely to survive and reproduce. Organisms which are poorly adapted to their environment are less likely to do so. Thus, the genes of the fittest organisms are those most likely to be passed on to offspring, to propagate through the population and, thus, predominate. It is through this selection process that life resists entropy.

It is important to note that mutations are not a consequence of changes in the environment. Rather, they pre-exist within a species’ variable genome and cause diversity in its population. When, the environment changes, most of a population may find itself unfit and die off. However, a small proportion carrying certain mutations may find itself to be fitter in the new circumstances and may, therefore, survive and propagate more successfully than it had in the past.

Most evolutionary biologists agree that, for the majority of species, natural selection operates at the level of the individual organism, i.e., inherited characteristics will cause the organism to behave in a way which maximises its own, and only its own, chances of survival and reproduction. However, there are a small number of species in which individuals display what has been referred to as “altruism”. That is, they will suffer a degree of disadvantage to their own survival and ability to reproduce to improve that of other members of their species. This has given rise to a number of competing theories of natural selection that I will discuss in my next post. However, before moving on to that topic, I would like to mention three important points.

Firstly, there is a difference between the meanings of “altruism” and “co-operation”. When an individual behaves altruistically, it acts in a manner which benefits the survival and reproductive chances of some other individual or individuals. This may disadvantage the former and there is not necessarily a payback. However, when an individual behaves co-operatively there is a payback. This is a subtle difference but of great significance in evolutionary theory. Do the small number of species referred to above behave altruistically or do they behave co-operatively? If the latter, then what is the payback?

Secondly, human beings differ from other species in several important ways. We have large brains with highly advanced cognitive skills which, among other benefits, enable us to identify opportunities and risks and to predict outcomes. We are also social animals and form groups. These groups have diverse cultures, i.e., ways of organising themselves, and we pass aspects of our cultures from one generation to another and from one group to another through social learning.

Finally, as systems grow ever more complex, they display emergent properties, i.e., properties of the system which are not held by its individual parts. Life is a collection of systems of increasing complexity, e.g., cells, multi-cellular organisms, groups of organisms, species, and eco-systems. As the level of complexity increases it can be expected that system properties will emerge. Thus, it is not necessarily the case that a property governing natural election at the cellular level will be the only property governing it at more complex levels. Other, emergent properties may come into play.

Natural selection, particularly in the case of human beings, is not a straightforward process therefore as will be discussed in my next post.

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01. Evolution a. Schrodinger's Other Paradox

Schrodinger’s Other Paradox

Have this article read to you.

There are significant features of living beings which distinguish them from all else in the known universe and which play a major role in human behaviour. To understand these, it is necessary to enter the realm of physics.

The explanation begins with the concept of time. Our human experience of time is that we move through it in one direction from the past to the present. This is known as “the arrow of time”. However, with two exceptions, the fundamental laws of physics do not dictate the direction of travel. They apply equally whether it is from the past to the future or from the future to the past.

The first exception is the second law of thermodynamics. The first and second laws of thermodynamics were developed in the 1850’s based on the work of Rankine, Clausius and Lord Kelvin. The first law states that energy cannot be created or destroyed and that the total amount of energy in the universe is constant. The second law states that, in a closed system, i.e., one into which energy cannot enter and from which it cannot escape, as energy is transformed from one state to another, some is wasted as heat. Importantly, however, the second law also states there is a natural tendency for any isolated system to degenerate from a more ordered, low entropy state to a more disordered, high entropy state. 

An important feature of the second law is that it defines direction in time and, thus, the arrow of time. The degeneration from a low entropy state to a high entropy states takes place as we travel through time from the past to the future. Were we to travel from the future to the past then the reverse would occur.

In the late 19th Century, the Austrian physicist Ludwig Boltzmann explained that entropy was a measure of the ways in which atoms and the energy they carry can be arranged and the probability of that arrangement. If atoms are arranged in an organized system, for example a crystal lattice, then they are in a low entropy state. However, if they are arranged in a more random and unstructured way, for example in a gas, then they are in a high entropy state. However, the probability of atoms being arranged in a crystal lattice is much lower than the probability of them being arranged as a gas. Thus, an orderly system has low probability and low entropy, a disorderly system high probability and high entropy. Entropy and disorder always increase in the direction of the arrow of time because the probability of a high entropy system is greater than that of a low entropy system.

Professor Brian Cox gives an excellent example in this Youtube video https://www.youtube.com/watch?v=uQSoaiubuA0.  In summary, the random arrangement of sand particles in a heap is far more likely than an arrangement that forms a sandcastle. So, as time progresses it is far more likely that a sandcastle will decay into a heap of sand than a heap of sand will arrange itself into a sandcastle.

Boltzman also suggested that, at some time in the distant past, the universe was in a low entropy state. This was dubbed the “Past Hypothesis” by Richard Feynman. However, Boltzman was unable to explain why this is the case and, to this day, this remains one of the unsolved problems of physics.

The second exception among the fundamental laws of physics is causality. In the direction of the arrow of time, a cause always precedes its effect and not vice versa. Were it possible for an effect to precede its cause the world would abound with time-travel paradoxes.

Attempts have been made to link, entropy, probability, and causality into a unified theory, but they have met with little success. Most authors believe that there is an undiscovered law associated with the initial and final states of the universe. Others believe that the law is associated with the nature of time and this defines the initial and final states. However, as matters stand at present, we simply have no explanation.

In 1944, another Austrian physicist, Erwin Schrodinger, raised an apparent paradox in his book “What is Life” which can be downloaded at www.whatislife.ie/downloads/What-is-Life.pdf. This was not his famous “Cat” paradox. Rather it is the tendency for living systems to become more organized as time progresses, which appears to contradict the second law of thermodynamics. Schrodinger thought that the basis of living matter evading decay to equilibrium was a “code-script” in the chromosomes of the organism “which determined the entire pattern of the individual’s future development and its functioning in the mature state”. At that time, DNA was yet to be discovered but Schrodinger’s work was significant in inspiring the necessary research.

There is no real paradox, however, because living beings are not closed systems. Rather they use free energy from the sun. In striving to maintain their integrity they increase entropy in their surroundings, and, in total, nett decay still occurs. Nevertheless, this anti-entropic behaviour is a distinctive feature of life.

Another distinctive feature of life, or of reasoning beings at least, is associated with causality. In the non-sentient universe, a cause must be certain and not merely possible if it is to produce its effect. It makes no sense to say “The traffic lights may turn green therefore the traffic moves off”. Rather, the traffic lights must turn to green. However, it does make sense for a human being to reason that “It is possible there will be an accident therefore I will drive carefully”. In this case the possibility of the accident causes careful driving. We are considering a possible risk and behaving in a manner which maintains our integrity.

So, in living beings there is also an association between entropy, causality, and probability but one which is significantly different from that seen elsewhere in the universe. The effect on human nature of this fundamental anti-entropic drive cannot be overstated as will be discussed in future posts.