Final answer:
Darwin's work laid the foundation for our understanding of how species change over time through natural selection. Mendel's work provided the basis for understanding how traits are inherited through genetics.
Step-by-step explanation:
Darwin's work on evolutionary theory is significant because it laid the foundation for our understanding of how species change over time. His theory of natural selection explained how certain traits that are advantageous for survival and reproduction become more common in a population over generations. This understanding has been crucial for modern biology and has helped us explain the diversity of life on Earth. Mendel's work, on the other hand, is significant for modern evolutionary theory because it provided the basis for understanding how traits are inherited from one generation to the next. Through his experiments on pea plants, Mendel discovered the principles of inheritance, such as dominant and recessive traits, and how traits are passed down through genes. This understanding of genetics has been integrated into modern evolutionary theory, allowing us to explain how variations in traits arise and are passed on.