The theory of evolution through natural selection unites biology in ways that are not usually evident to most peoplE) A non-biologist might look at a lake and see ducks swimming and dragonflies flying. When a biologist looks at the lake, he/she probably would see

Organisms better adapted to the environment  

Explanation:

According to the evolutionary theory proposed by Charles Darwin in "The Origin of Species" (1859), the fittest organisms are those that are better suited to the environment (i.e., have a higher fitness). These organisms have more chances to survive and reproduce, and thereby they have also more chances to leave their genes in the next generation. This process is the central concept of evolution, and it is called natural selection. In consequence, evolution produces phenotypic changes or 'adaptations' that are inherited by organisms over generations, and certain traits are lost during this process.