Final answer:
Richard Lenski's experiment with E. coli demonstrated natural selection by observing the bacteria's adaptation to their environment over generations, leading to the emergence of advantageous traits.
Step-by-step explanation:
Richard Lenski's long-term experiment with E. coli bacteria demonstrates the process of natural selection. Lenski's research provided insights into how populations evolve through the accumulation and distribution of advantageous mutations over thousands of generations. By allowing E. coli to reproduce in a controlled environment with limited resources, certain traits were consistently favored. This selection pressure led to the emergence of bacterial populations with improved adaptation to their environment. Importantly, the experiment showcased real-time changes in genetic frequencies within the population, which is one of the central aspects of the theory of evolution by natural selection.
One of the significant findings from Lenski's research was the evolution of a bacterial strain that could metabolize citrate under aerobic conditions, which E. coli normally cannot do. This adaptation demonstrated a clear instance of evolution. The experiment did not show speciation, genetic drift, or extinction, but rather the gradual change of a population through selection pressures. These E. coli populations became better suited to their environment over time due to the iterative process of natural selection sensing changes in the organisms' genomic composition.