Introduction To Evolution - Natural Selection

Natural Selection

Further information: Common descent

In the 19th century, natural history collections and museums were a popular pastime. The European expansion and naval expeditions employed naturalists and curators of grand museums showcasing preserved and live specimens of the varieties of life. Charles Darwin was an English graduate who was educated and trained in the disciplines of natural history science. Such natural historians would collect, catalogue, describe and study the vast collections of specimens stored and managed by curators at these museums. Charles Darwin served as a ship's naturalist on board the HMS Beagle, assigned to a five-year research expedition around the world. During his voyage, Darwin observed and collected an abundance of organisms, being very interested in the diverse forms of life along the coasts of South America and the neighboring Galapagos Islands.

Charles Darwin gained extensive experience as he collected and studied the natural history of life forms from distant places. Through his studies, Darwin formulated the idea that each species had developed from ancestors with similar features. In 1838, he described how a process he called natural selection would make this happen.

Darwin noted that orchids exhibit a variety of complex adaptations to ensure pollination; all derived from basic floral parts.

The size of a population depends on how much and how many resources are able to support it. For the population to remain the same size year after year, there must be an equilibrium, or balance between the population size and available resources. Since organisms produce more offspring than their environment can support, not all individuals can survive out of each generation. There must be a competitive struggle for resources that aid in survival. As a result, Darwin realized that it was not chance alone that determined survival. Instead, survival of an organism depends on the differences of each individual organism, or "traits", that aid or hinder survival and reproduction. Well-adapted individuals are likely to leave more offspring than their less well-adapted competitors. Traits that hinder survival and reproduction would disappear over generations. Traits that help an organism survive and reproduce would accumulate over generations. Darwin realized that the unequal ability of individuals to survive and reproduce could cause gradual changes in the population and used the term natural selection to describe this process.

Observations of variations in animals and plants formed the basis of the theory of natural selection. For example, Darwin observed that orchids and insects have a close relationship that allows the pollination of the plants. He noted that orchids have a variety of structures that attract insects, so that pollen from the flowers gets stuck to the insects’ bodies. In this way, insects transport the pollen from a male to a female orchid. In spite of the elaborate appearance of orchids, these specialized parts are made from the same basic structures that make up other flowers. In his book Fertilisation of Orchids Darwin proposed that the orchid flowers were adapted from pre-existing parts, through natural selection.

Darwin was still researching and experimenting with his ideas on natural selection when he received a letter from Alfred Wallace describing a theory very similar to his own. This led to an immediate joint publication of both theories. Both Wallace and Darwin saw the history of life like a family tree, with each fork in the tree’s limbs being a common ancestor. The tips of the limbs represented modern species and the branches represented the common ancestors that are shared amongst many different species. To explain these relationships, Darwin said that all living things were related, and this meant that all life must be descended from a few forms, or even from a single common ancestor. He called this process descent with modification.

Darwin published his theory of evolution by natural selection in On the Origin of Species in 1859. His theory means that all life, including humanity, is a product of continuing natural processes. The implication that all life on Earth has a common ancestor has met with objections from some religious groups. Their objections are in contrast to the level of support for the theory by more than 99 percent of those within the scientific community today.

Natural selection is commonly equated with survival of the fittest, but this expression originated in Herbert Spencer's Principles of Biology in 1864, 5 years after Charles Darwin published his original works. Survival of the fittest describes the process of natural selection incorrectly, because natural selection is not only about survival and it is not always the fittest that survives.