Darwin’s Theory of Evolution: Natural Selection and Variability
Darwin’s Theory of Evolution
Evolution according to Darwin’s theory: The next step in the evolutionary theories of Charles Darwin, who made his work public in his 1859 Origin of Species, in which he formulated his theory of the evolution of living beings called Darwinism. Darwin conceived his theory after a trip to the coast of South America and the Galapagos Islands, which are about 960 km from the continent.
Darwin’s Observations
Darwin’s observations: Plants and animals on the east coast of South America were different from those on the west coast. Species gradually changed along the coasts. The animals and plants of the Galapagos Islands were very different from their continental counterparts. He discovered 14 different species of finches, each of which was characteristic of an island. As the islands were of volcanic origin, the animals and plants’ ancestors had to come from the continent. With the data collected, he wrote the following principles for the evolution of organisms:
- Species with similar characteristics have evolved from a common ancestor.
- The evolutionary changes that affect living things are slow, gradual, and continuous, culminating in the appearance of new species.
- The process of natural selection was the mechanism to evolve species.
Evolution by Natural Selection
The evolution by natural selection: Darwin knew that selective breeding of domestic animals was successful. This process, which breeders called artificial selection, involved choosing individuals with the desired features to cross-promote, generation after generation. This mechanism of artificial selection gave Darwin a clue as to how natural selection works. Nature, through the environment, chooses the breeding pair. Darwin explained that individuals better adapted to the environment survive and reproduce. Darwin came to these conclusions based on observations that populations are capable of producing more descendants than necessary to perpetuate the species. For example, a female mouse has 8 litters per year with 14 young in each litter. If all descendants survived and reproduced, the offspring of mice would reach more than 45 million.
The number of individuals in a population remains more or less constant. Darwin explained this as the struggle for existence due to limited resources. Natural selection is a process that acts on the variability of the population, favoring the best-adapted individuals. Among individuals in a population, there are small differences that are transmitted through inheritance and allow those who have them to better adapt to environmental changes, so natural selection favors them.
Variability in Populations
Variability: The origin of the population: Genetic variability increases the chances of survival of a given species because it produces greater variety. The variability in individuals of the population is a result of mutations and the adaptation of genes and individuals to the environment.
Mutations as a Source of Variability
The mutations as the source of variability: In Darwin’s time, there was a lack of knowledge of genetics. It was necessary to explain the origin of the diversity of individuals that occurs within a population. Thanks to scientific knowledge, we now know that the primary cause of heritable variability is mutations. We also know that many mutations are harmful, while some are beneficial.