Ancestral species are organisms from which later species have evolved. They represent the common ancestors in the evolutionary tree, showing how different species are related through time. For example, the common ancestor of humans and chimpanzees existed millions of years ago, leading to the diverse species we see today. Studying ancestral species helps scientists understand the process of evolution and how traits are passed down through generations. Fossils and genetic evidence provide insights into these ancient organisms, revealing how they adapted to their environments and contributed to the biodiversity we observe in the present.