Darwinism – Theory and Explanation

Theories of Natural Selection – Darwinism

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

Evolution states that various types of plants, animals, and other living organisms on earth have their origin in pre-existing life forms. The distinguishable differences are due to modifications or adaptations in successive generations.

Explanation:

Ideas revolving around natural selection and evolution began to be discussed in earnest in the early nineteenth century. Whenever the theory of evolution is mentioned, the name Charles Darwin often comes up. However, the work and ideas of many others helped to shape our current understanding of evolution.

Also, as our technological and scientific techniques improve and our knowledge of the principles of evolution grows, our understanding of the processes of evolution will also improve. Many scientists have put forward their theories of evolution over the course of 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.

Charles Darwin – the Father of Evolution:

Charles Darwin (1809-1882) was an English naturalist of the 19th century. The early 1800s was a time when new discoveries were changing the scientific view of the world. Geologists were learning that the world was very old and had also suggested that the world we see today is constantly changing. During Darwin’s time, biologists were saying that life on earth had also changed, and the process of change over time is called evolution.

Darwin was influenced by C. Lyell (Geologist), who believed that the natural forces that existed in the past are the same as those existing at present. Darwin is popularly known as the father of evolution due to his contribution to the establishment of the theory of evolution.

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

The Journey of the Beagle:

Charles Darwin, as a naturalist, traveled the world extensively from 27th December 1831 to October 1836 on the HMS Beagle, a British military ship. The Beagle sailed from England to South America and other parts of the world. Darwin spent time in South America, visiting remote islands such as the Galápagos Islands.

The Galapagos Islands are around 1000 kilometers off the coast of South America. The majority of Darwin’s time on the Galapagos Islands was spent studying nature, gathering samples of unknown plants and animals, and writing about places and organisms that few others had ever seen.

On the Galapagos Islands Darwin noticed many new animals and plants that he had never seen. He examined and noted the similarities and differences between the animals, fossils and animal remains from other islands. Many of the turtles, birds, and lizards he found on the Galápagos were similar, but not identical, to organisms he discovered on the South American mainland.

Darwin deduced that some of the organisms on the Galápagos must have originated in South America and over time, they evolved to be different.

Darwin observed that the tortoises on the Galapagos Islands were similar but larger in size as 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, he concluded that there are three patterns of biological diversity:

• Species vary around the world: Darwin explored habitats in South America, Australia, and Africa. He had found large, flightless birds called rheas that resembled ostriches in South America. Since ostriches live only in Africa and rheas live only in South America, he concluded that species vary around the world.
• Species vary locally: Consider the example of the tortoises of the Galapagos He also found diversity in the tortoise of the Galapagos islands. For example, Tortoises from Isabela Island have dome-shaped shells and short necks as vegetation on this island is abundant and close to the ground. Whereas the Hood Island tortoises have curved and open shells around their long necks and legs.

This enables them to reach the island’s sparse, high vegetation. With such observations, Darwin concluded that species vary locally as well.

• Species vary over time: Darwin also had a huge collection of fossils. Fossils are the preserved remains of pre-existing organisms. Darwin observed that some fossils that were collected did not look like living organisms, but others did. For example, the extinct glyptodont lived where armadillos live today and also looked like a giant armadillo.

Darwin’s Finches:

Darwin also studied over 13 finch species in the finches of the Galápagos Islands. He observed that the finches on each island differed from the finches on the other islands as well as from the finches on the mainland.

A major difference was the shape of their beaks. This was due to the different types of food eaten by them. For example, the large ground finch had a wide and strong beak to crack open big, hard seeds. This beak works like a nutcracker. The small tree finch had a long and narrow beak that was compatible with catching insects in the trees.

The cactus finch had a tough beak which it used for eating cactus parts and insects. The beak works like a pair of needle-nose pliers. The warbler finch has a small narrow beak that it used to catch small insects. The beak works like a pair of tweezers. Darwin concluded that finch beaks were adjusted for the type of food they eat.

Darwin wondered why all the finches’ showed differences despite the fact that they lived on islands only 80 kilometers apart.

He hypothesized that the island finches had descended from South American finches. He explained that an ancestral species of finch 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 successive generations, they developed adaptations that allowed them 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.

Darwinism:

When Darwin returned to England after his expedition, he began to formulate a theory regarding the evolution of adaptations. Darwin’s theory of evolution through natural selection is often referred to as Darwinism.

Darwinism Encompasses the Following Fundamental Ideas:

1. Species change over time. As the environment changes, an organism’s requirements also change, and they adapt to the new conditions. This trend of changing over a period of time as per the natural requirements is known as adaptation.
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. We usually refer to billions of years while talking about the time period in evolution. It is a gradual process as the changes and adaptation take a long time to stabilize and give rise to a new species.
4. Natural selection is the method of evolution.

Natural Selection:

Natural selection means that organisms with traits that are best suited to their environment are more likely to survive and reproduce. These favorable traits are passed on to the next generation.

The inherited traits that favor an organism’s survival and reproduction in a specific environment are called adaptations. Adaptations only spread through a population in future generations if natural selection favors them.

Darwin postulated that if groups of organisms have a common ancestor and 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 the large number of species on Earth today.

The Process of Natural Selection Takes Place in Four Steps, Which Are as Follows:

1. Overproduction of offspring: All organisms produce more offspring so that more can survive to adulthood and reproduce.
2. Inherited variation and adaptation: variations that help an organism survive and reproduce better are inherited and passed on to the next generation.
3. The struggle for existence: organisms struggle to survive due to environmental factors like predators, food supply, disease, and climate affecting the size of a population.
4. Natural selection: Individuals with favorable variations survive better and reproduce in a particular environment and are thus selected by nature. Whereas those with unfavorable variations perish. As a result, organisms with favorable variations will have more offspring and pass on these favorable traits compared to individuals without those features.

Evidence Supporting Darwinism:

The long neck of the Giraffe is an adaptation to pluck and eat more leaves from tall trees. This adaptation became permanent in life for survival. The taller giraffes could survive in famine heat areas; as a result, this adaptation was transmitted to their offspring. In this way, the present long-necked giraffe came to existence.

Black-colored peppered moths evolved gradually as new species due to the industrial revolution.

DDT spray is used to destroy all types of mosquitoes. However, some mosquitoes developed a resistance to DDT and survived. Such tolerant mosquitoes survived and reproduced, giving rise to more tolerant offspring.

Drawbacks of Darwinism:

• He considered small fluctuating variation as primary factors which are not heritable and not part of evolution.
• He also did not differentiate between somatic and germinal variation and considered that all variations are heritable.
• He did not explain the ‘arrival of the fittest.’ He failed to explain the cause, origin, and inheritance of variations and vestigial organs, nor he could explain the extinction of species.
• Darwinism also could not explain the existence of neutral flowers and the sterility of hybrids.
• Inheritance of over-specialized organs e.g., antlers in deer and tusks in elephants.