"Descent with modification" is a key concept in the theory of evolution by natural selection. It refers to the idea that species change over time and that newer species are modified versions of older species. In other words, all living organisms are descended from earlier, different organisms, and changes occur in species over time through the accumulation of small modifications in their physical and behavioral traits.
Charles Darwin first introduced this concept in his book "On the Origin of Species", in which he proposed that all living organisms have evolved over time from common ancestors through the process of natural selection. This theory has been supported by a vast amount of evidence from many fields of science, including biology, genetics, paleontology, and more.
Examples of descent with modification include the evolution of humans from earlier primates, the evolution of birds from dinosaurs, and the evolution of whales from land mammals. Other examples include the evolution of antibiotic-resistant bacteria and the development of different varieties of crop plants through selective breeding.