Evolution and Natural Selection

The theory of evolution states that all living organisms on Earth have evolved from common ancestors that existed billions of years ago.

This process of evolution, which has taken place over vast spans of time, has resulted in the diversity of life we see today. The theory of evolution helps to explain how organisms have changed and adapted to their environments over time. These changes have led to the emergence of new species and the extinction of others.

Natural selection

The theory of evolution by natural selection, proposed by scientist Charles Darwin, explains the process by which organisms evolve over time.

According to this theory, there is natural variation within a population of organisms. Those that are well-adapted to their environment have a better chance of surviving and reproducing. So, they can pass on their genes to the next generation.

On the other hand, individuals that are not well-adapted to their environment are less likely to survive and reproduce. This results in the loss of their genes from the gene pool.

This process results in the survival of the fittest, as those individuals with beneficial traits are more likely to pass on their genes to the next generation.

For example, in a population of mice, the mice that are better at finding food and avoiding predators are more likely to survive and reproduce. However, the mice that struggle to do so may not survive long enough to pass on their genes.

Three illustrated scenes showing the natural selection process with mice and a fox. The first scene depicts a fox on a mound surrounded by a higher number of white mice than dark mice. The caption reads, "White Mice Population is Greater than Dark Mice Population". In the second scene, the same fox is seen with fewer white mice around, and the caption states, "White Mice are More Visible to the Fox Thus, White Mice are Eaten More". The third scene portrays the fox with an increased number of dark mice in comparison to the white ones, and the caption mentions, "Next Generation contains Higher Number of Dark Mice". Above the three scenes are additional captions: "Some Mice are Eaten by the Fox" above the first, and "The Surviving Mice Reproduce" above the third.

Over time, the small differences in characteristics and traits between individuals within a species can accumulate. This can lead to the evolution of that species. If enough time passes, the species may change so significantly that it becomes a new, distinct species. This new species will be unable to reproduce with the original species.

Natural selection in peppered moths

Variation in the peppered moth population

The process of natural selection can be observed in the case of the peppered moth. This is a species in which individuals show variation in their colouration. Before the British Industrial Revolution, the majority of the peppered moth population was pale in colour.

Pale moths were better adapted to their environment than the darker moths. This is because their colouration provided camouflage against the trees, making it harder for predators to spot them. As a result, more pale moths were able to survive and reproduce, passing on their genes to the next generation.

In contrast, the dark moths were more visible to predators and thus less likely to survive and reproduce, leading to a decrease in their numbers in the population.

The industrial revolution and its impact on the peppered moth population

However, during the Industrial Revolution, pollution from factories caused the trees to become blackened with soot. This resulted in a shift in the advantage between pale and dark-coloured moths.

Previously, the pale moths had an advantage due to their camouflage against the trees. However, the blackened trees now made the pale moths more visible to predators, while the dark moths were better able to blend in. As a result, the dark moths were more likely to survive and reproduce, passing on their genes to the next generation.

The resulting shift in the population

Over time, this led to an increase in the number of dark moths in the population and a decrease in the number of pale moths.

A graph with a curve showing a distribution of moths. On the left side, there are lighter coloured moths, and as we move to the right, the moths become progressively darker. Above the curve, there are three red downward arrows pointing towards the lighter moths, while two green upward arrows point towards the darker moths. There's an axis on the left, but no specific labels are provided. The image suggests a change in moth population, with a decrease in lighter moths and an increase in darker ones.

This means that the population of moths was evolving in response to the changing conditions of their environment. Previously, pale-coloured moths made up the majority of the population, but as the environment changed, the dark-coloured moths became better suited to the new conditions. Therefore, they had a higher likelihood of surviving and reproducing.

As a result, the proportion of dark-coloured moths in the population increased over time, eventually becoming the majority. This demonstrates how natural selection can lead to changes in the characteristics and traits of a population over time.

Evidence for Evolution

Fossil records provide evidence supporting Charles Darwin’s theory of evolution by natural selection. They show the changes that have occurred in organisms over long periods of time.

By studying the fossil record, scientists can see how different species have evolved and adapted to their environments. This supports the idea that natural selection plays a role in shaping the diversity of life on Earth.