Module 6: evolution part 1
Describe three ways in which natural selection can affect a population over time
- directional selection
- stabilizing selection
- Disruptive selection
In directional selection, the phenotype is favored over genotype causing allele to move in one direction and hence creating certain traits in an organism. The favored alleles are therefore dominant over the other alleles. For example, in a community that consist of bird with a length of 2cm and grain eater, after a long period and a change of food available the length of beak can change gradually. The dominant allele leads to the required change in the shape of the beak so that it is in with the kind of food that the bird feeds on.
In stabilizing selection a populations expresses dominance in particular traits due to because of decreased genetic diversity. For example, in an instance where there are too many tall trees and few short trees, the short tree cannot compete for sunlight and therefore it has been acted by stabilization selection. Here the natural selection brings about balance thereby rolling out any existing competition.
Disruptive selection in natural selection is regular changes in a population genetics where different traits are discovered due to diversified genetic disorders. For example, in a community of moths, a usually light in colors though after a period of like nine months darks moths in color appear in the generation. In human being, this can also occur whereby individuals who have been observed with soft hair in many generations can at any random generations be observed to have hard and rough hair (Audesirk, 2011).
What is sexual selection? How is sexual selection similar to and different from other forms of natural selection?
Sexual selection occurs in situations whereby individuals select their mate due to the character those mates portray. Sexual selection can be either by contest or by choice. For example, in sexual selections by contest is when members of one sex in a community of animals are sexually oriented to one opposite sex in the same community. In a sexual contest, the mate, which appears as the best and strongest among them, carries the day. In a community of lions for instance, the males sometimes have to fight for mates and the one, which emerges the winner remains with the lioness’ while the others, flees away. Therefore, in sexual selection by contest there is survival for the fittest because those organisms, which cannot win the contest, may not be able to get a mate.
Sexual selection by choice on the other hand refers to same sex character competing for attention towards the opposite sex. Their similarity is that sexual selection and Disruptive selection and directional selection select the best traits. Here there is no need for competition because an individual chooses his or her mate. This applies in human beings whereby one chooses a person of the opposite sex to marry without being forcefully coerced. Some animals and insects in the ecosystem also exhibit the same behavior; most plants however just compete for mates hence do not experience sexual selection by choice.
Unlike other forms of natural selections, sexual selection only deals with mating and not survival for the fittest. Failure to posses traits of sexual selection only limits reproduction and procreation but cannot cause death unlike other forms of selections whereby if an organism does no posses certain traits it may easily become extinct (Audesirk, 2011).
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Both the theory of evolution by natural selection and the theory of special creation (which states that God simultaneously created all species) have had an impact pm evolutionary thought. Discuss why one is considered a scientific theory and the other is not.
Evolution by natural selection is considered a scientific theory because no supreme being is involved in creation. The scientists performed several tests before concluding that indeed evolution by natural selection is scientific. Natural selection is a mechanism for the entire evolution theory, and it goes hand-in-hand with migration, mutation, and genetic drift. It is practical and based on observation and not superstitions or beliefs in supernatural beings. Therefore, it is a scientifically proven theory that outlines the reasons why plants and animals are the way they appear.
The theory of special creation on the other hand is based on the belief that God is the creator of all the plants and animals. In a natural selection perspective, life exists in diverse forms, depending on the environment that support it. This means that different species live on different localities for instance; some are adapted to the waters, air, and soils. Theory of natural selection expounds further that living things have varying abilities to respond to changes in the environment hence the way they reproduce is different.
Additionally, special creation theory cannot be subjected to any scientific test to prove whether it is based on the facts or it is just mere claims. Natural selection on the other hand, is based on elements that can be examined in the forms of cells, atoms, and molecules in relation to the environmental changes. Natural selection theory argues that plants and animals are made up a mass of cells thus serving as a practical evidence for it to be considered scientific. In natural selection, there is survival for the fittest whereas in the theory of special creation God determines the survival of plants and animals (Audesirk, 2011).
In many countries, conservationists are trying to design national park systems so that “islands” of natural area (the big parks) are connected by thin “corridors” of undisturbed habitat. The idea is that this arrangement will allow animals and plants to migrate between refuges. Why would migration be important?
The habitat corridors are habitat areas of habitat that connects different wildlife habitats separated by human activities. The main reason of designing the big parks in such a manner is to allow inbreeding and reduce genetic diversity, which is normally evident with isolated populations. Random events usually eliminate some populations from a given habitat and therefore, corridors helps in re-establishing populations. A corridor is a solution to the ever-growing threat of habitat fragmentation, urbanization and other human activities that displaces plants and animals from their natural habitat. It also helps to ensure that both plants and animals freely migrate from one habitat to another freely without disturbance. Generally, corridors protect plants and animals by stabilizing colonization, migration, and interbreeding.
In the history of evolution, migrations under natural selection has been ruled out to be the best mechanism for living organism to find better ways in which they can adopt to the environment that fits best their adaptations. The sole purpose of conservationist is to build national parks that best fit each living organism’s community. Each living organism is unique and deserves an environment that fits all their traits. Therefore, it would be right if we said that the purpose of conservationist is to save all living organism though it is not practical. Adding to this, living organism migrate in order to congregate with organism of the same community for breading purposes (reproduction). Other organisms migrate to other locations where they can find an amenable location that fits all their traits. For example, some birds have been observed to fly to cities. According to researcher, this kind of birds that are commonly observes in cities and towns find the environment amenable to live in. moreover, there are other organism migrate at night. According to the theory of natural selection, the organisms that migrate at night are a mechanism that helps them to stay away from their predators. This form of migration is known as Diel vertical migration commonly observed in the ocean and sea (Audesirk, 2011).
Reference
Audesirk, T., & Audesirk, G. (1999). Biology: Life on earth. Upper Saddle River, N.J: Prentice Hall.
