Final answer:
Natural selection is a key mechanism in evolution involving the selection of advantageous traits that allow individuals to have higher survival and reproduction rates, leading to changes in a population's characteristics over time.
Step-by-step explanation:
Natural selection is a fundamental force of evolution where individuals in a population that possess advantageous traits are more likely to survive, reproduce, and pass on these traits to their offspring. As a result, the characteristics of organisms change over time, adapting to their environments. Key aspects of natural selection include variation in traits within a population, differential survival and reproduction due to these traits, and inheritance of the beneficial traits. It's important to note that natural selection works on existing genetic variation within a population. It cannot create new traits but can only 'select' from the variations that are present, which may arise through processes such as mutation and gene flow. The fitness of an organism, which is its relative ability to survive and produce offspring in a given environment, also plays a crucial role in natural selection. The concept of 'fitness' is central because those individuals with the greatest fitness are typically the ones most successful in passing on their genes to the next generation.