How does natural selection work?

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Nov 6, 2016

Answer:

General speaking, something must cause differential reproduction and then better suited individuals will survive over time.

Explanation:

Natural selection is the process in which individuals whom are better suited to their environment will have an increase in fitness. It occurs over multiple generations and can take a very long period of time to occur.

For natural selection to occur, the following must be true:
1. There must be variation in traits (every individual can't be identical)
2. There must be differential reproduction (some individuals are more likely to reproduce than others)
3. Traits are passed on from generation to generation

Thus, the first step in natural selection is that something must cause differential reproduction. This could be the introduction of a predator, a disease, a random mutation that is detrimental, a change in resource availability such as a drought, and so forth.

This image shows how a genetic mutation is unfavorable and is selected against, but the same process holds for a gene that is unfavorable during any scenario.
https://en.wikipedia.org/wiki/Evolution

This event causes some individuals to survive and reproduce and some to be less successful. For example, a predator is introduced and it hunts and kills mostly individuals with shorter legs that run slowly. Or the environment undergoes a long drought and individuals in the species who have a gene that helps them perspire (sweat) less are more successful.

Over multiple generations, the genetic composition of the species changes. Maybe within six generations the predator has completely wiped out individuals with shorter legs. Maybe within two generations the drought completely eliminates individuals with a gene that results in excess perspiration. The amount of time will vary.

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Aug 26, 2016

Answer:

Natural selection works by acting on existing variation within a population so that individuals with greater fitness survive.

Explanation:

Natural selection works with variation in traits that naturally exists within a population. Individuals with the greatest fitness survive. Fitness in ecology refers to an individual's ability to survive and produce viable offspring. Natural selection ensures that traits that are beneficial and increase fitness remain in the population while traits that are harmful and decrease fitness do not.

Let's look at the evolution of a giraffe's long neck. Giraffes did not evolve long necks because they needed to reach leaves higher in trees. This is NOT how natural selection works and is an example of Lamarckism. Instead, there was natural variability in the length of giraffes' necks that existed in the population. Those with longer necks were able to eat more food because they could reach taller branches, were healthier, and produced more offspring because of this advantage.

Over many generations of giraffes, those with longer necks are more successful and those with shorter necks are less successful and their numbers decline until all giraffes have long necks. The image below illustrates the idea:

http://laevolucionsp.weebly.com/the-natural-selection-of-darwin-and-wallace.html

It is important to note that natural selection acts on an individual's phenotype, or the expression of the gene, as opposed to genotype.

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