Generations, or lineage, refer to the sequence of ancestors and descendants in a family tree. Each generation typically spans about 20 to 30 years, marking the time it takes for individuals to grow up, reproduce, and raise their own children. This concept helps trace familial connections and understand the heritage of individuals. Lineage can be categorized into direct lines, such as parents and children, and collateral lines, which include siblings and their descendants. Understanding lineage is important for studying genetics, cultural heritage, and historical relationships within families, often represented in diagrams called family trees.