Final answer:
The reproductive advantage for well-suited organisms in an environment is called natural selection, where traits that enhance survival and reproduction are passed on, leading to evolutionary changes in a population.
Step-by-step explanation:
The reproductive advantage enjoyed by organisms that are best suited to a particular environment is known as natural selection. This concept is fundamental to the theory of evolution and was famously described by Charles Darwin. Natural selection refers to the process by which individuals with traits that confer a survival or reproductive advantage are more likely to pass on their genes to the next generation. Over time, this leads to the accumulation of these advantageous traits within a population. An example of an adaptation produced by natural selection is the development of better running speed, which might help an individual to escape predators or to hunt more effectively.
Adaptation is another key term related to natural selection. It describes a heritable trait that improves an organism's ability to survive and reproduce in its environment. Changes in genetic variation over time enhance or maintain the suitability of a population to its surroundings, like the variations in finch beaks enabling them to access different food sources. This illustrates the mechanisms by which populations evolve through the process of natural selection.