What about the modern organisms Darwin studied to the idea of descent with modification?

Darwin studied a diverse range of modern organisms to support his idea of descent with modification, also known as evolution through natural selection. By observing variations within and between species, as well as the process of adaptation to different environments, he was able to build a compelling case for the gradual transformation of species over time. Studying modern organisms provided evidence for the idea that all life on Earth is interconnected through a common ancestor.