Darwin’s Theory of Evolution – Natural Selection

Darwin’s Theory of Evolution: Variation and Adaptation 

 Key Concepts

• Evolution
• Darwin’s voyage
• Darwin’s fiches
• Darwin’s theory of evolution
• Adaptations
• Selective breeding
• Natural selection
• The process of natural selection

Introduction

Evolution is the theory that suggests that all types of living things that exist today have been developed from life forms that existed earlier. In simple terms, evolution can also be defined as change over time. 

Modern scientists have altered this definition of  evolution as genetic change in a population over time. 

Many scientists have put forward their theories of evolution over time; Charles Darwin was one of them. 

Even though he was not the first person to talk about evolution, he was the first person to write the most comprehensive collection of evidence supporting evolution. 

Explanation

Charles Darwin: 

Charles Darwin (1809-1882) was an English naturalist of the 19th century. A naturalist is someone who examines the natural world, such as plants, rock formations, and animals. He is popularly known as the father of evolution due to his contribution to the establishment of the theory of evolution. 

His theory helped to eliminate all of the ancient beliefs that the origin of various species was a supernatural occurrence or act of the Almighty. Darwin’s evolutionary theory of natural selection provided a more reasonable explanation for the creation of new species. According to natural selection, various species originated from a single species as a result of adaptation to change in environmental conditions. 

Darwin’s theory also changed the natural sciences and serves as the foundation of a lot of biological research today. 

Darwin’s voyage: 

Charles Darwin was only 22 years old when he got an invitation to serve as a naturalist on the HMS Beagle, a British military ship. 

In December 1831, Charles Darwin went on a voyage on the HMS Beagle, a British military ship. He was 22 years old when he accepted an invitation to serve as a naturalist on the HMS Beagle. The Beagle sailed from England to South America and other parts of the world to provide navigational maps. The Beagle’s journey would take nearly five years. 

Darwin spent time in South America, visiting remote islands such as the Galápagos Islands. The Galápagos Islands are around 1000 kilometres off the coast of South America. The majority of Darwin’s time was spent studying nature, gathering samples of unknown plants and animals, and writing about places and organisms that few others had ever seen. 

Darwin’s observation: 

On the Galapagos Islands, Darwin noticed many new animals and plants that had not been recorded before this trip. He became especially interested in studying the similarities and differences between the animals and animal remains from other islands. 

Many of the turtles, birds, and lizards he encountered on the Galápagos were similar, but not identical, to organisms he discovered on the South American mainland. Darwin deduced from these observations that some of the animals and plants on the Galápagos originated in South America and evolved to be different over time. 

Darwin found that the tortoise on the Galapagos Islands was similar but larger compared to their native species on the mainland. He also observed various species of birds on the Galapagos Islands. Finches were one such species he studied extensively. With the help of these observations, Darwin gave his theory of evolution. 

Darwin’s Finches: 

The finches of the Galápagos Islands differed a little from the finches in Ecuador. Also, the finches on each island differed from the finches on the other islands. He found a difference in the shape of their beaks. He described 13 finch species, although, at the time, he thought they were all the same species. 

The shape of finch beaks differed due to the type of food eaten. Darwin concluded that finch beaks were adapted for the kind of food they ate. He began to think about why and how the finches became different. 

The large ground finch has a wide and strong beak to crack open big, hard seeds. This beak works like a nutcracker. 

The small tree finch in Figure 5 has a long and narrow beak that is compatible with catching insects in the trees. 

The cactus finch has a tough beak to eat cactus parts and insects. The beak works like a pair of needle-nose pliers.  

The warbler finch has a small narrow beak to catch small insects. The beak works like a pair of tweezers. 

Darwin’s thoughts: 

Darwin hypothesized that the island finches had descended from South American finches. An ancestral finch species from the mainland may have somehow ended up on the Galapagos Islands. The finches of that species migrated to different environments where they had to adapt to different conditions. 

Over many generations, they developed adaptations to get enough food to survive and reproduce. Every group of finches became isolated from the other groups. Eventually, each group evolved into a different species. When Darwin returned to England from his voyage, he developed a theory about how the adaptations evolved. 

Darwin’s theory: 

Darwin learned from geologists that the Earth was formed slowly over a long period of time. Natural processes like sedimentation and erosion slowly altered their surface over time. Darwin reasoned that organism populations changed slowly as their environment changed slowly. A species may become extinct (all members die out) if the habitat changes abruptly as a result of an event such as a flood, an earthquake, or a volcanic eruption. 

He also used fossils as evidence that species evolve over a long period of time. He discovered fossils of species that lived a few million years ago that resembled living species. 

In Darwin’s time, animal and plant breeders utilized selective breeding to produce organisms with the traits they desired. Darwin referred to selective breeding as an artificial selection because the breeders chose the desired traits to produce alterations in a species over a few generations.  

Darwin believed that in wild animals and plants, the traits were chosen by the environment. He referred to this process as natural selection. He believed that natural selection took longer than artificial selection because it occurred by chance. 

Origin of species: 

In 1859, Darwin published the results of his study in a book called On the Origin of Species by Means of Natural Selection. 

Based on his investigations and evidence, Darwin concluded that: 

1. Organisms change over time. 

2. All organisms are descended by the process of branching from common ancestors. 

3. Evolution is a slow process that takes a long time to complete. 

4. Natural selection is the mechanism of evolution. 

Natural selection: 

Natural selection is the process through which organisms with favorable adaptations survive and reproduce at a higher rate than organisms with less-favorable adaptations. Inherited traits that increase an organism’s chances of survival and reproduction in a certain environment are termed as adaptations. 

Adaptations only spread through a population in future generations if natural selection favors them. Darwin spent a lot of time figuring out how natural selection might lead to adaptation in a species and then to the evolution of a new species.  

He postulated that if groups of organisms having a common ancestor are isolated from other organisms of the same species, natural selection acts on them to become different over generations. The separated groups adapt to different environmental conditions, and this process can develop a new species. With enough time, this could explain a large number of species on Earth today. 

Process of natural selection: 

1. Overproduction: 

All organisms produce more offspring so that more can survive to adulthood and reproduce.  

This means that many of those offspring will die without reproducing.  

Only the survivors are able to reproduce and pass their traits on to their offspring. 

2. Inherited variation: 

Most characteristics that an organism has are inherited or passed from parent to offspring. 

Every individual has their own combination of traits. 

Offspring vary in traits such as color and size, etc. 

3. Struggle to survive : 

Environmental factors like predators, food supply, disease, and climate affect the size of a population. 

We know that a species produces too many offspring, and only a certain number survive; the survivors are better adapted to their environment than those who die. 

Offspring of the survivors would inherit the favorable adaptations. Organisms with unfavorable adaptations die before they can pass them on to offspring. 

4. Successful reproduction: 

Individuals with inherited variations can survive better and reproduce in a particular environment. 

As a result, they will have more offspring and pass on these favorable traits compared to individuals without those features.  

Summary

• Evolution is the theory that suggests that all types of living things that exist today have been developed from life forms that existed earlier.
• Charles Darwin was an English naturalist of the 19th century and is popularly known as the father of evolution.
• His theory helped to eliminate all of the ancient beliefs that the origin of various species was a supernatural occurrence or act of the Almighty.
• Charles Darwin went on a voyage on the HMS Beagle, which sailed from England to South America and other parts of the world. He visited remote islands such as the Galápagos
  Islands
• Darwin studied various species on the Galapagos like tortoises, finches and lizards.
• He concluded that all the finch species must have evolved from an ancestral species of
  finch from the mainland.
• Darwin gave the concept of selective breeding, where the breeders chose the desired
  traits to produce alterations in a species over a few generations.
• Darwin concluded that:

1. Organisms change over time.
2. All organisms are descended by the process of branching from common ancestors.
3. Evolution is a slow process that takes a long time to complete.
4. Natural selection is the mechanism of evolution.

• Natural selection is the process through which organisms with favorable adaptations survive and reproduce at a higher rate than organisms with less-favorable adaptations.
• The process of natural selection takes place in four steps:
  

1. Overproduction
2. Inherited variation
3. Struggle for existence
4. Successful reproduction