Genetic variation in a population is caused by different versions of genes called alleles. Natural selection is a process where certain factors cause changes in the frequency of alleles that favour organisms suited to survive. This happens because organisms with advantageous traits are more likely to survive and pass on their genes to their offspring, leading to evolution. Mutations can create new alleles, some of which can be beneficial for survival. Those organisms with the beneficial alleles are more likely to survive and pass on their genes to their offspring, increasing the frequency of those alleles in the population. Check out our article on Gene Mutations to learn more about the different types of mutations.

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Natural selection example

Let's take an example of a small population of mice  have which helps in the sand and avoid predators, while the remaining 10% have light fur, which makes them more visible to predators. Because the light-furred mice are more vulnerable to predation, their population size is lower compared to the dark-furred mice. However, a hotel is being built on the beach, and the owners decide to add white sand to the beach, making the dark-furred mice more visible to predators, and the light-furred mice better camouflaged. Over time, as the dark-furred mice are preyed on more frequently, the frequency of the light fur allele in the population increases, and light-furred mice become more common than dark-furred mice. This change in allele frequency is an example of natural selection in action.

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What is the theory of natural selection?

Charles Darwin was an English naturalist who developed the idea of natural selection after studying plants, animals, and fossils during his five-year voyage to South America and the Pacific islands. His book, On the Origin of Species, which was published in 1859, introduced the concept of natural selection to the world. Alfred Russell Wallace independently conceived the idea of natural selection around the same time.

During Darwin's time, genes were not yet known, but he observed that traits were passed from parents to offspring in the he studied. Darwin named his theory natural selection to differentiate it from artificial selection, which was a popular hobby of selective breeding among people. For example, through selective breeding of pigeons, distinct breeds with fancy feathers or acrobatic abilities could be created. Darwin argued that a similar process of selective breeding occurred naturally in the environment without human intervention, and he used natural selection to explain the process of evolution. Check out our article on Artificial Selection to learn more about selective breeding.

Stages of natural selection

These are the four stages of natural selection proposed by Charles Darwin.

1. Overproduction: More organisms are born than can survive. This means that there is competition for limited resources, such as food and shelter.
2. Variation: Characteristics vary within a species. No two individuals are exactly alike, and there is variation in traits like size, color, and behavior.
3. Inheritance: Variations are inherited. Offspring inherit traits from their parents, and these traits can be passed down through generations.
4. Differential survival and reproduction: There are differences in survival and reproduction due to variations. Some variations may help an organism survive and reproduce better in its environment, while others may be less advantageous. Over time, the individuals with advantageous variations are more likely to survive and pass on their traits to their offspring, while those with less advantageous variations are less likely to survive and reproduce. This leads to a gradual change in the characteristics of a population over time, which is the process of evolution by natural selection.

What is exponential growth in a population?

In theory, every individual in a population can reproduce and contribute to the growth of the population. If every individual survived to adulthood (or the stage of reproductive maturity) and reproduced, and all their offspring did the same, the population would experience exponential growth.

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However, exponential growth can only be sustained when nothing limits survival and reproduction. Several environmental factors prevent populations from increasing infinitely as it affects their survival rate. These are known as selection pressures.

Selection pressure examples

Selection pressures can be either abiotic or biotic and affect an organism's chances of survival. Abiotic factors include non-living factors such as light, water, and temperature, while biotic factors include living factors such as predation, competition for resources, and disease (e.g., parasites).

These factors can limit the maximum size of a population, meaning that not all individuals produced will be able to survive. Those that are suitably adapted to their environment will live on to reproduce, passing on their advantageous traits to their offspring. Over time, these advantageous traits become more common in the population, while less advantageous traits become less common or even disappear completely. This process leads to changes in the gene pool of a population, which is the total collection of alleles of all genes in a population.

What is fitness in biology?

are as's ability to survive and reproduce in its environment. When individuals possess the favored phenotypes that increase their chances of survival and reproduction, they have higher fitness than those who do not possess these traits.

Phenotypes are the observable physical or behavioral characteristics of an organism that are the result of the interaction between its genetic makeup and its environment. An organism's fitness is determined by how well its specific phenotype allows it to cope with and survive in its environment.

Over time, the traits that confer higher fitness become more common in a population as they are more likely to be passed on to future generations. This process, known as natural selection, is a key mechanism driving evolution, as it leads to changes in the genetic makeup of a population over time.

What is evolution?

Evolution is the change in the heritable characteristics of populations over several generations, and it is made possible by natural selection acting upon variation within a population. Through evolution, populations can adapt to suit their environmental conditions.

However, it is important to note that evolution and speciation are related but distinct concepts. Evolution is the process by which populations change over time, while speciation is the process by which one species splits into two or more distinct species.

Speciation occurs when populations of the same species become reproductively isolated from one another, meaning they can no longer interbreed and produce viable offspring. Over time, these populations may accumulate enough genetic differences that they become distinct species with their own unique characteristics.

So while evolution can lead to speciation, not all evolutionary changes result in the formation of new species.

Why is variation crucial for natural selection and evolution?

Variation is crucial for evolution to occur. Without variation in a population, there would be no differences for natural selection to act upon. Adaptation is only possible because there is genetic variation within a population that allows for some individuals to possess traits that are better suited for survival in their environment.

In a large population with a wide range of phenotypes, not all individuals will be optimally adapted to the current environment. However, some individuals will possess that are better different conditions, their generation. This process of natural selection acting on variation within a population is what drives evolution.

Over time, genetic variation can accumulate within a population, leading to the formation of new species or the adaptation of existing species to new environments. This is why variation is so important for process of evolution to occur.

What happens when a population becomes too small?

are absolutely right! Natural selection is a key process driving evolution, and it describes how individuals with certain traits that are better suited for survival and reproduction are more likely to pass those traits on to the next generation.

However, as you noted, smaller populations with less genetic variation are more vulnerable to sudden changes in their environment. Chance events, such as genetic drift, can have a greater impact on the survival of a small population. Genetic drift is the gradual change in allele frequencies in a small population due to chance rather than natural selection. This can lead to the loss of certain alleles or the fixation of others, which can have long-term effects on the genetic makeup of a population.

Overall, natural selection is influenced by a variety of factors, including selection pressures such as predation and competition, as well as genetic variation within a population. Understanding the interplay between these factors can help us better understand the process of evolution and how different populations adapt to their environments over time.

Natural Selection

Who first developed the theory of evolution by natural selection?

Charles Darwin is credited as the scientist who first offered the theory of evolution by natural selection. The theory was also conceived independently by Alfred Russell Wallace.

How does natural selection lead to evolution?

Natural selection is the mechanism through which evolution takes place. It leads to changes in the heritable characteristics of populations over several generations. 

How does natural selection occur?

Individuals who are well suited to their environments (i.e., individuals with high fitness) are more likely to survive and reproduce. It follows that individuals who are not well suited to an environment will not be able to survive and reproduce, and their frequency will dwindle. Over time, the population becomes fitter and more adapted to its environment. 

What is natural selection?

Over time, the selection pressures acting on a population can create changes in the allele frequencies of certain genes, leading to changes in the phenotype frequency. Natural selection is the differential survival and reproduction of individuals due to differences in their phenotype. 

What are the 4 stages of natural selection?

Random mutations produce new alleles. The new allele puts the organism at an advantage to survive selection pressures, such as predation and disease. The well-suited organism will survive and reproduce offspring which will inherit the advantageous allele. Over several generations, the advantageous allele will dominate the gene pool of a population.

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