Natural Selection: Definition, Darwin's Theory, Examples and Facts (2023)

The concept of natural selection was first formally proposed at a Linnean Society biology conference. On July 1, 1858, a joint document on the subject was presented and later published. It included contributions from Charles Darwin andAlfred Russel Wallace.

Both wrote about the idea that natural selection contributed to Earth's evolution through evolution.Survival of organisms best suited to their environment. Scientists at the time realized that evolution took place, but they did not know how species evolved.

After this introduction to natural selection, Darwin expanded on the subject with his theory of evolution and his book,On the origin of species, published in 1859. His work on Darwin's finches and his ideas onsurvival of the fittestexplained the mechanism of natural selection and how it could lead to the proliferation of many different types of organisms.

Definition of natural selection

Evolution is the cumulative change in the characteristics of an organism or population over the next few generations. It is sometimes summarized asdescent with modification. Natural selection is one of the mechanisms that drive evolution.

To be an active trait or a trait that causes natural selection, the trait must have the following characteristics:

  • heritability.A trait can influence evolution through natural selection only if it is passed from parent to offspring.
  • functionality.The characteristic must have a function. The traits must do something for natural selection to take place.
  • Advantage.To be selected for transmission to offspring, the trait must confer an advantage on the organism that possesses it, or make it better able to survive in its environment.
  • Origin.The trait must have caused organisms to evolve because it made organisms that possessed it better able to survive. If organisms changed due to another mechanism, such as genetic mutation, it was not due to natural selection.

Natural selection and Darwin's theory of evolution

From the fossil record, it is clear that species change over time and new species develop while others die out. Before Darwin, there was no explanation of how such changes could occur.

Heevolution theorydescribes what happens when the characteristics of some individuals of a species become predominant andnatural selectiondescribes how this dominance occurs.

Darwin studied natural selection in finches. Even when another mechanism, such as mutation, changes a population, if the mutation does not confer a natural advantage, it may disappear due to natural selection.

How natural selection works

Within a species, a typical population includes individuals with varying characteristics because they receive half of theirGenetic codefrom the father and the other half from the mother. For genetically based traits, this combination of parental genes results in a wide variety of traits in individuals in the population.

The combination of traits in some individuals gives them an advantage in foraging, reproduction, or resistance to predators or disease. Other individuals are given traits that place them at a disadvantage.

Favored individuals will live longer and produce more offspring. Their offspring will mainly receive genes that result in advantageous traits. Over time, the majority of the population will evolve with the advantageous characteristics and the disadvantages will disappear. Natural selection selected theindividuals with positive traits.

Darwin's Voyage on the Beagle

In 1831, the British Navy sent the exploration ship HMS Beagle on a mapping expedition around the world. Charles Darwin came on board as the naturalist in charge of observing the local fauna and flora. The expedition lasted five years and spent a lot of time along the Atlantic and Pacific coasts of South America.

Leaving South America to cross the Pacific to New Zealand, the ship spent five weeks exploring the Galapagos Islands. As he did elsewhere, Darwin made extensive notes on the characteristics of the plants and animals he encountered. Eventually, these notes would form the basis for the development of the concept of natural selection and his theory of evolution.

Darwin's FinchesProvenSurvival Of The Fittest

Back in England, Darwin and an associated ornithologist examined Darwin's notes on the finches of the Galapagos Islands. The islands apparently were home to 13 different species of finches, while the nearest South American landmass, 600 miles away, had just one species. The main difference between the species was thenipple size and shape.

Darwin's analysis of his notes led him to the following conclusions:

  • The finches haddifferent peaksbecause they lived on different islands indifferent environments.
  • The environment did not cause the differences in the peaks because there was no mechanism for such an influence.
  • The different beak characteristics must have been present in the original finch population.
  • As the finches of the original population settled on an island, the pointed finchesbetter adapted to the local food supplywould have an advantage.
  • Which finches are best suited for the food source on your islandsurvive in greater numbersthan less adapted finches.
  • Eventually, over many generations, finches on an island would form a distinct species with different beak size and shape, because the finches with those beaks would be best suited to their environment.

With these conclusions, Darwin explained the evolution of the beaks of finches in the Galapagos Islands, proposing themechanism of natural selection. He summarized this mechanism assurvival of the fittest, where fitness was defined asreproductive success.

Darwin's work was based on three observations

For his conclusions, Darwin drew on his notes, his own observations, and his interpretation of the writings ofThomas Robert Malthus. Malthus was an English polymath who, in 1798, published his theory that population growth will always exceed the food supply. The corollary is that, in any given population, many individuals will die due to competition for a limited food supply.

The three observations that allowed Darwin to develop his theory of evolution and natural selection were:

  1. Individuals in a population show variation in traits such as color, behavior, size, and shape due to genetic variation.
  2. Some of the traits are passed from parent to child and are hereditary.
  3. Parents in a population overproduce offspring so that some do not survive.

Based on these observations, Darwin proposed that individuals with traits that make them more fit would survive, while less fit individuals would die. Over time, the population would be dominated by individuals with the traits that made them fitter.

Natural selection Examples: bacteria

Populations of bacteria exhibit very strong natural selection because they can multiply so quickly. They usually multiply until they reach a limitation, such as lack of food, space or other resources. At that point, the bacteria best suited to the environment will survive, while the rest will die.

An example of natural selection in bacteria is the development ofantibiotic resistance. When bacteria cause an infection and the individual is treated with antibiotics, any bacteria that have the antibiotic resistance trait will survive while all others will die. The proliferation of antibiotic-resistant bacteria is a major medical problem.

Examples of Natural Selection: Plants

Plants evolve to adapt to their environment through natural selection. Some plants develop flower colors to attract pollinators of a specific type and develop special mechanisms to spread their seeds. They have to adapt to more or less sunlight and fight pests.

Cacti are an example of natural selection in plants. In the desert where they live, there's plenty of sunlight, little water, and the occasional animal that would love a juicy bite.

As a result, cacti have developed compact bodies or small, succulent leaves with thick bark to protect themselves from the harsh sun and minimize water loss. They can also store water and have sharp edges to discourage animals. Cacti with these characteristics were the fittest and are still evolving.

Another example is the shift in the mustard plant field caused by drought in Southern California. To survive drought, plants must grow, flower, and distribute their seeds quickly. Southern California field mustard plants that flowered early became dominant, while those that flowered later died.

natural selection in animals

Animals are more likely to influence their survival because they can engage in complex behavior patterns. The characteristics that can determine fitness fall into three main categories. The ability to find enough food through hunting or gathering is the key to survival.

Most animals havepredators, and specific features allow them to avoid being eaten. Finally, the ability to find and attract a mate allows them to pass on their positive traits to their offspring.

Typical characteristics that influence natural selection include:

  • Movement.The ability to run, swim or fly quickly determines whether an animal can successfully hunt or escape predators.
  • Camouflage.If an animal manages to hide successfully, it can escape predators or ambush prey.
  • Immunity.Some animals will be more resistant to a disease than others and will survive.
  • Fortaleza.Competing for a mate often involves tests of strength with other members of the same species.
  • Senses.Animals that can see, smell or hear better may have a better chance of surviving.
  • sexual characteristics.Natural selection in animals depends on successful reproduction after attracting a mate.

Animals continually evolve, first to adapt better to a given environment and then, if the environment changes, to the new environment. Natural selection can cause evolutionary changes in existing populations, and it can also favor one species over another if two species compete for the same space and resources.

Natural selection Examples: animals

Natural selection in animals is best observed when the environment changes in some way and animals with specific traits become better adapted and soon become dominant.

For example, the London speckled moth was light in color with dark spots. During the industrial revolution, buildings were blackened with soot. The birds could easily see the light-colored moths against the dark background, and soon only the dark-colored moths remained. Natural selection favored moths with larger, darker spots.

In another example, let's say some insects become resistant to a chemical pesticide very quickly. Even if only a few individuals are resistant, the rest will die and the resistant insects will survive. Insects normally produce large numbers of offspring, so insects with resistance genes will quickly take over.

In an example of reproductive preference, female peacocks choose mates based on the size and brightness of their tails. after effects ofnatural selection, almost all male peacocks today have large, colorful tails.

Although Darwin is best known for his publications on the theory of evolution, it is natural selection that drives change and adaptation in species. Charles Darwin's 1858 paper, with contributions from Alfred Russel Wallace, whose paper was published at the same time, forever changed the way people viewed evolution and the natural changes in plants and animals that occurred continuously over time.

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