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.