Common usage of the word ‘evolution’ conveys the idea that living things in our world have come into being through processes starting from a primeval mass of subatomic particles and radiation, over approximately 20 billion years.
A more precise understanding of the above statement divides the ‘atoms to people’ transition into four realms:
• Cosmology is the branch of astronomy that deals with the origin, and formation of the general structure of the universe.
• Biogenesis refers to first life—the production of living organisms from inanimate matter.
• Microevolution or speciation refers to population and species change through time. There are many published examples of speciation if, by the development of a new ‘species’, we mean the development of a new population of individuals, which will not breed, with the original population to produce fertile offspring. Micro evolution is a scientific fact, which no one, including creationists, disputes.
• Macroevolution or general evolution refers the progression to more complex forms of life. The mechanisms of macroevolution are still being researched and there is no definitive theory to explain the process.
The popular mechanisms lor explaining micro evolution are ‘mutation’ and ‘natural selection’.
Mutations are ‘mistakes’ introduced into the genetic ma-terial used for reproduction, which can occur for example as a result of exposure to radiation. Naturally occurring mutations are rare, and it is acknowledged that of those that do occur, almost all have a negative effect (in fact, some creationists argue there is not a single known case of a truly positive mutation, one having no negative side-effects). The occasional positive mutation, giving some benefit to the organism, provides the ‘new material’ for natural selection to operate on.
Natural selection is based on the observation that there is variation among individuals in a population. Natural selection states that those individuals who possess some advantage in the environment (such as being a faster runner) are more likely to leave more offspring, thereby increasing the probability of passing the advantage on to future generations. Natural selection is what ‘retains’ the occasional positive mutation and causes the population to ‘advance’ is some way.
Consider the case when we treat a bacterial infection with an antibiotic. Among the billions of bacteria there may be some that possess resistance to the antibiotic. The process of natural selection will now result in the survival of the bacteria with the immunity and their percentage in the general population will be higher. Given sufficient time, the majority of the bacteria will have this advantageous immunity.
A classic example of natural selection that is often quoted in the literature on the subject is the peppered moth changing its predominant colour in response to environmental pollution during the industrial era of England. Here, the predominance of white moths was shifted to dark moths, allowing for camouflage against predatory birds, as the trees darkened due to industrial pollution. Before the population shift occurred, both light and dark moths were present.
The environment allowed one shade to flourish. However, what if the pollution covering the trees on which they rested was a bright purple, making both the light and dark moths highly visible. Would the moths become purple? Experiments and knowledge to date demonstrate that adaptation has limits beyond which no more change is possible.