Moving forces of evolution

Introduction

Previous chapters looked at evidence of biological evolution. This chapter looks at Darwin's theory of moving forces of evolution. It will also look at scientific experiments proving this theory.

Genetic diversity

Earth's environment has been changing since our planet was formed. There were periods when it changed drastically and there were periods when changes were slow and subtle. When environmental changes are too drastic, organisms become extinct or evolve into new types of organisms.

The DNA of all organisms is composed of thousands of genes. Some of these genes are active and some are not. These inactive genes are sometimes are called 'nonsense genes'. The inactive genes might not do anything in the given environmental circumstances but they might be 'switched on' if the environment changes. Genes do not become activated quickly. For example, if the climate suddenly becomes colder, hairless animals will not grow warm fur right away.

Even though all living things are made of the same 'material' there are no completely identical organisms. They all differ slightly in size, body shape, body hair thickness, limb length and more. These differences occur due to their genetic diversity. Genetic diversity is genetic variation within a population or species. See image 1.

Natural selection

In our example, the process of activating fur-producing genes would probably go like this:

When the climate suddenly becomes colder, most organisms will die of cold and only individuals with some sort of body hair will survive. Organisms that have traits allowing them to survive the environmental crisis will probably be the only ones able to reproduce. Their traits will be more common in the next generation.

In our example, these slightly furry individuals will breed, producing offspring that will consist of animals that have fur and animals that do not. Again, only the furry ones will survive. This furry generation will produce mostly furry offspring. Thousands of years later there will be a new type of species with long, thick fur that would keep them warm in cold climate. These furry individuals survived because they were 'selected' by nature. Natural selection is the concept developed by Charles Darwin which states that genes which produce characteristics that are more favourable in a particular environment will be more abundant in the next generation. A generation with new features will be created. Evolution of the population will have occurred. See image 2.

Genetic mutations

For most species, the process of evolution takes a very long time, so it is difficult to follow. It is possible to follow the 'scaled down' version of evolution with laboratory bacteria, though. Bacteria have a short life span, multiply very quickly and mutate easily, creating great genetic diversity. If a large dose of antibiotic is added to a bacterial colony, there will be a mass die-off. But a few of the bacteria will survive because they are resistant to the antibiotic. These resistant species were formed by chance, due to genetic mutations. Genetic mutation, or genetic polymorphism, is a change in the nucleotide sequence of a DNA molecule. As mentioned before, genetic mutations arise by chance. They may or may not equip the organism with better means for surviving in its environment. But if a gene variant improves its adaptation to the environment, the organisms carrying that gene are more likely to survive and reproduce than those without it. These 'survivors' will produce a generation that will be even more resistant to antibiotics, thus leading to the 'invincible' generation of bacteria.

This same phenomenon of bacterial evolution can occur in human bodies when medication fails to cure the disease. So, please, do not abuse the power of prescription antibiotics.

Conclusion

Evolution is the process by which all life forms change slowly over time because of slight genetic variations passed down from one generation to another. Evolution is a slow process that takes thousands or millions of years. Biological evolution is a continuous process that will stop only when all living forms cease to exist. See image 3.

The driving forces of evolution are natural selection and genetic drift. The term ‘genetic drift' refers to a change in the frequency with which a gene appears in a particular population. Genetic drift acts on genetic variation created by mutation, genetic recombination (an offspring's genetic re-shuffling') and gene flow (genetic transfer from one generation to another). Natural selection is the process by which organisms with environmentally suitable traits are more likely to survive and reproduce and pass those traits to their offspring.