Which of the following traits is a result of natural selection?

The correct answer is a characteristic that improves reproductive success. This reflects a fundamental principle of natural selection, where individuals with certain traits that enhance their ability to survive and reproduce in a given environment are more likely to pass those advantageous traits on to the next generation. Traits that improve reproductive success increase the likelihood that those traits will become more prevalent in the population over time.

Natural selection acts on heritable variations within a population, favoring those that contribute positively to reproductive success and overall fitness. This process can lead to adaptations over generations, making organisms better suited to their environments. The focus here is on traits that directly affect reproductive output, making them crucial in the natural selection process.

The other options, although related to aspects of biology, do not encapsulate the essence of natural selection as it pertains to reproductive success. Random mutations may introduce new traits but do not directly imply they will enhance survival or reproduction. Environmental stress can lead to physical changes, but these changes are not necessarily inherited or advantageous. Lastly, a trait expressed by all organisms in a population does not imply that it provides any selective advantage, as it may not contribute to increased reproductive success in the context of natural selection.