Natural Selection vs Sexual Selection
There are several types of selections such as natural selection, sexual selection, artificial selection etc. Selection of organisms is defined as some sort of functional relationship between fitness and phenotype. Selection is the basic concept which helped Charles Darwin to introduce his theory of evolution. Some people describe that the sexual selection is a special form of natural selection. Darwin mainly used the concept of sexual selection to introduce and understand certain aspects of the reproductive biology of animals that he was unable to ascribe to natural selection. However, there are some differences between these two concepts. Darwin noted that many sexual characteristics are caused due to the process of natural selection, but certain changes are made due to both forms of selection.
What is Natural Selection?
Any coherent difference in fitness among phenotypically different organism is known as natural selection. The ability of survival and reproducibility of an organism is used to measure fitness of that particular organism.
Darwin explained his theories of evolution using the concept of natural selection. According to him, natural selection is the key driving force of evolution. The main idea of natural selection is that members of population compete with each other for resources (such as mates, foods, habitats etc) and the members who are well-adapted to their lifestyle, have a better chance of survival. Eventually the members who survive, may pass their advantageous traits to the next generation and revolutionize the field of evolution.
What is Sexual Selection?
Sexual selection is another type of selection which involves the selection of traits based on their role in courtship and mating processes. In other words, it is the mating success among individuals in a particular population. Those who mate successfully may pass their traits to the next generation and that would enhance the mating success.
The struggle between individuals of one sex for the possession of the other sex or the opposite sex generates the sexual selection process. According to Darwin, the concept of sexual selection may be subdivided into two aspects namely, intrasexual selection and Intersexual selection. Intrasexual selection involves competition between members of the same sex for individuals of the opposite sex. Intersexual selection is the preferential choice of mates by one sex relative to the other sex.
Natural Selection vs Sexual Selection
• Sexual selection enhances mating success or the number of copulations, while natural selection tends to produce well-adapted individuals to their environment. Sexual selection does not adapt the individuals to their environment.
• Unlike sexual selection, natural selection acts on traits which increase the fitness of members in a population.
• Certain adaptations have been derived from the sexual selection which could never have been arisen from natural selection alone (Ex: the neck of the giraffe, various plumages of most male birds etc.)
• Generally sexual selection depends on the success of one sex while natural selection depends on the success of both sexes in relation to the general condition of life.
• Sexual selection is a special type of natural selection, but the traits which involve mating preferences may have no benefit other than the fact that they produce attractive offspring with special mating characters.
• The characteristics, which have been arisen from sexual selection, may be useless except for mating purposes, but the characteristics that have been arisen from natural selection result usually in new adaptations, in individuals.
• Unlike in the natural selection, there are terms called male choice and female choice in the sexual selection.
• In most of the animals, certain traits related to their sexual selection process do not express their characteristics until the organism is able to mate, but naturally selected traits may occur at birth of the organism during the process of natural selection.
Andreas Svensson says
This dichotomy between sexual an natural selection is not in line with current scientific theory. Darwin coined Natural Selection in order to distinguish it from Artificial selection (because he used breeding as another example of a mechanism of evolution) in his book Origin of species.
Natural selection is understood to be selection in nature for individuals that are better adapted to their environment. You write “Sexual selection does not adapt the individuals to their environment.”. Well, yes it does, for females are A PART OF a male’s environment, just like rival males are.
The way we understand natural selection today is that an organism has to pass a great number or hurdles in order to pass its genes to the next generation. For example, it has to survive parasited, avoid predators, find food, handle adverse temperatures, obtain a partner and rear young. There can be many more. All of these are subject to natural selection. Selection for the ability to obtain a partner is called sexual selection, and is therefore not in contrast to, but a subset of, Natural selection.
This is today standard evolutionary theory. The confusion in your text is all too common, however. One reason is that natural selection is seen to have to do with the SURVIVALof the organism. But Natural selection has actually to do with the propagation of the organism’s genes into the next generation. That an individual survives is only a part of what it needs to do. If it survives to a high age but never have offspring, its fitness is zero.
Another source of confusion is the obvious trade-off between Sexual selection and individual survival. For example, a peacock with a huge train is more likely to be taken by predators. But ALL the different aspects of fitness are traded off against other aspects of fitness. A bluetit that has packed on fat during a winter’s day has a higher chance of surviving the cold at night, but is less likely to escape an attack from a sparrow hawk. A fast sprinter has less endurance. And so on.
Sexually selected traits may reduce individual survival. So it is traded off against Viability, not the survival of the organism’s genes. Natural selection concerns the sum of all adaptations of the organism and Sexually selection is part thereof.
If we tweak Spencers catch phrase slightly, this becomes obvious: “The reproduction of the fittest”