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.
All too often, natural selection is couched in terms of differential death rates, with the strongest and fastest individuals considered as having a selective advantage over weaker and slower individuals.