Biology Regents Practice Exam

Natural selection is most rapid in which type of species?

1. Species with long reproductive cycles

2. Complex multicellular organisms

3. Pathogens killed by antibiotics

4. Species with short reproductive cycles

The correct answer is: Species with short reproductive cycles

Natural selection tends to occur more rapidly in species with short reproductive cycles because these organisms can reproduce quickly and frequently, allowing for a greater number of generations to occur in a relatively short period of time. This fast reproduction facilitates the spread of advantageous traits throughout a population, as beneficial mutations can be passed on more rapidly and increase in frequency. For example, bacteria, which often have very short generation times, can show significant evolutionary changes in just a few days or weeks. This allows them to adapt to environmental pressures, such as antibiotics, very swiftly. In contrast, species with long reproductive cycles, such as many larger animals, reproduce less frequently, which slows down the process of natural selection. Similarly, while complex multicellular organisms can exhibit traits shaped by evolution, their longer life spans and reproductive cycles decrease the speed at which natural selection can drive change. Pathogens that are killed by antibiotics can demonstrate rapid evolution, but they do so primarily because of their short generation times rather than their classification as pathogens, reinforcing the concept that short reproductive cycles enhance the process of natural selection.