A stroke can result in a number of visual problems, including visual neglect, decreased visual acuity, diplopia (double-vision), squint, and homonymous hemianopsia (visual field defects).
Natural Selection. Natural selection is the process by which individuals with characteristics that are advantageous for reproduction in a specific environment leave more offspring in the next generation, thereby increasing the proportion of their genes in the population gene pool over time.
New varieties. Natural selection and selective breeding can both cause changes in animals and plants. The difference between the two is that natural selection happens naturally, but selective breeding only occurs when humans intervene. For this reason selective breeding is sometimes called artificial selection. Different varieties of plants and animals with desired characteristics can be developed by selective breeding. For example: 1  cows that produce lots of milk. 2  chickens that produce large eggs.