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 consequence of natural selection on the genetic structure and evolution of organisms is complicated. Natural selection can decrease the genetic variation in populations of organisms by selecting for or against a specific gene or gene combination (leading to directional selection).