Final answer:
Organisms change little over time due to gradual evolution occurring over many generations. Factors such as gene changes and generation time influence the rate of evolution. Fossil records and the redistribution of organisms provide evidence of evolution.
Step-by-step explanation:
Organisms change so little over so much time because evolution is usually a gradual process that occurs over many generations. The rate of evolution depends on various factors, such as the number of genes that have changed and the generation time of the species. While some organisms, like bacteria, can undergo rapid evolution and have observable changes within a short period of time, others, like humans, evolve slowly over millions of years.
Evidence of Evolution: Fossil records and studying the distribution of organisms across the planet provide evidence of how organisms have changed over time. These physical changes occur over enormous time spans and help explain the process of evolution.
Natural Selection: Natural selection acts on individual organisms, shaping an entire species over thousands or millions of years. Although changes can occur in a single generation, it takes a long time for an entire species' genotype to evolve.