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.
The term natural selection is most often defined to operate on heritable traits, because these directly participate in evolution. However, natural selection is blind in the sense that changes in phenotype can give a reproductive advantage regardless of whether or not the trait is heritable.