Darwin’s theory of evolution by natural selection is the foundation of modern evolutionary biology. It states that species evolve over time through a process in which individuals with certain traits are more likely to survive and reproduce than those without them. This process is known as “survival of the fittest”, and it explains why certain species have adapted better to their environment than others. Darwin argued that this process was driven by random variation in individual traits, and he proposed that natural selection acted on these variations to produce new species. In other words, he suggested that individuals with advantageous traits were more likely to survive and pass on their genes to future generations, while those with less advantageous traits were less likely to do so. As a result, over time, the overall population would become increasingly adapted to its environment.