Naturalist Charles Darwin was born in England (1809-1882) and is well known for his theory of natural selection. At 22, Darwin was allowed to sail across the world on the HMS Beagle. This five-year trip around the world (1831-1836) saw the ship visit various areas worldwide, including South-East Asia, the southern point of Africa, the coast of South America, several Atlantic Ocean islands, and some South Pacific islands.
Charles Darwin researched these islands' geology, flora, and wildlife during his journey. He noticed other islands far apart yet had comparable climates, and geography had diverse flora and fauna. Flora and fauna of adjacent islands were connected, but they differed from one another and from plants and animals found on the mainland.
When HMS Beagle sailed to the Galápagos Islands, roughly 600 miles off the west coast of South America, he saw a variety of plants and creatures that differed from one island to the next. He noticed that the Galápagos Islands featured a variety of bird species that were not seen anywhere else in the globe, yet similar ones occurred on South America's west coast.
He saw 13 distinct types of birds, each living on a different island and somewhat different. He discovered that the difference was in the size and form of their beaks. He also observed that the varied types of beaks were related to the sort of food they ate. These birds were likewise distinct from those found on South America's continent. These birds are now often referred to as Darwin's finches. Darwin discovered that the fossils of the Galápagos Islands resembled living organisms in South America.
According to Darwin, the finches of the Galápagos Islands must have migrated from South America's continent. The ancestral forms then adapted to the climatic circumstances of the many islands and evolved into various species. Darwin noticed that gigantic tortoises diverged from one another on different islands. Later that year, in 1838, Darwin was inspired by Thomas Malthus's "Principles of Population."
According to Malthus, the reproduction rate in plants and animals is extremely high. The pace of population expansion follows a geometric trend, but the rate of food supply grows in an arithmetic ratio. As a result, a lack of food leads to competition among living things for existence. The Malthusian article substantially inspired Darwin's concept of natural selection.
Two facts support Darwin's hypothesis −
All organisms are variable.
All creatures create many more offspring than they can sustain.
According to Darwin, natural selection is based on five postulates −
Overproduction
Competition
Natural Selection and Survival of the fittest
Variation
All living things reproduce in a geometric progression to ensure their species' survival. The quantity of children generated exceeds the available food and space; if unchecked, it will quickly deplete the available space and food. Elephants, for example, are the slowest breeders, beginning breeding at 30 and producing only six offspring throughout 90 years. A single elephant pair will generate around nineteen million descendants if all children survive for 750 years. On the other hand, a single evening primrose plant produces an average of 1,18,000 seeds. Imagine what would happen if all the seeds grew into an evening primrose plant. In 48 hours, Paramecium divides three times. Imagine the repercussions if all of its children survive and proliferate.
Darwin discovered that space remained relatively constant. As previously said, food supply grows in an arithmetic ratio, whereas population grows in a geometric ratio. As a result of overcrowding, people compete for space and food. The battle for survival might take the following forms −
Intraspecific − Competition between members of the same or closely related species.
Interspecific conflict − Conflict between organisms of various species living together for food and reproductive grounds.
Environmental struggle − Struggle against physical causes such as severe temperatures, scarcity or lack of space, scarcity of food and water, drought, earthquake, volcanic eruption, and so on.
As a result, he discovered that no two people are alike. Even the offspring of the same parents were not the same. Darwin discovered that variety occurs in living creatures, no matter how minor. We now understand that variety is the most critical component in evolution. Evolution cannot occur in the absence of variety.
Darwin discovered that members of a species with superior qualities better suited to existing and changing environmental conditions lived and reproduced more effectively than those with inferior features. In this battle for survival, the unfit or less fit creatures with inferior features died.
Competition among organisms forces them to alter and adapt to their surroundings. If these alterations are inherited, the species' overall character will be changed. These modifications were given the term variation by Darwin. He has also discovered that not all of the differences are relevant regarding evolution. Some differences become favorable in the survival fight and are handed down to the following generation. These are inherited variations. Some genetic variants are detrimental and are not handed on to future generations. These changes eventually result in the extinction of the species.
Useful Variations are handed on to the following generation. Individuals of a species accrue these differences. However, our environment is unstable and constantly changing, which causes further modifications and the creation of new adaptations in species. As natural selection proceeds, these creatures become significantly distinct from their ancestors after several generations, leading to the emergence of new species. Let us look at the giraffe example from Darwin's point of view once again.
According to Darwin, the ancestors of giraffes had variable-sized necks. The vegetation of the habitat is altered in response to environmental changes. The grasses and bushes were decreased and replaced by towering trees. Nature preferred gaffes with long necks because they had a greater chance of reaching higher tree branches/foliage and accessing more food. This gave them more incredible energy and a reproductive edge over giraffes with shorter or medium-sized necks. As a result, more giraffe offspring with longer necks were generated in the following generations. Over many generations, these long-necked giraffes outcompeted the shorter-necked giraffes. Darwin proposed that the long-necked giraffe would have developed in this manner.
Charles Darwin's theory of natural selection is based on his five-year trip around the world on the HMS Beagle. During his journey, he noticed a variety of plants and creatures that differed from one island to the next. He discovered that the finches of the Galápagos Islands must have migrated from South America's continent and evolved into various species.
He was also inspired by Thomas Malthus's "Principles of Population" which states that the reproduction rate in plants and animals is extremely high, leading to competition among living things for existence. Darwin's postulates of natural selection are based on five postulates: Overproduction, Competition, Natural Selection and Survival of the Fittest, and Variation.
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